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Links April 2014

Yves Rossy is the Jetman, he flys with a wing and four jet engines strapped to his body, he gave an interesting TED talk about flying along with some exciting videos [1].

Larry Brilliant gave an informative and inspiring TED talk about stopping pandemics [2]. I thought that Smallpox was the last disease to be eradicated but I was wrong.

Michael Shermer gave an interesting TED talk about pattern recognition and self deception [3]. It’s a pity that the kissing prank shown at the end only pranked women, they should be less sexist and prank men too.

Raffaello D Andrea gave an interesting TED presentation about “Athletic” quadcopters [4]. It’s very impressive and has the potential for several new human/machine sports.

Lisa D wrote an insightful article about Prejudice Spillover discussing the way that people who aren’t in minority groups only seem to care about injustice when a member of the majority is targetted by mistake [5].

Ron Garret wrote an insightful post about the Divine Right of Billionaires which debunks some stupid arguments by a billionaire [6]. Ron says that “it’s often instructive to examine incorrect arguments, especially when those arguments are advanced by smart people” and demonstrates it in this post.

Lisa D wrote an interesting post about her problems with financial aid bureaucracy [7]. She intended the post to be a personal one about her situation, but I think it illustrates problems with the various aid programs. If aid was available to her with less bureaucracy then she would be doing paid work, completing her studies, and heading towards post-graduate studies.

Mark Shuttleworth wrote an insightful article about ACPI, security, and device tree [8]. It’s the first time I’ve seen a good argument for device tree.

TED presented an interesting video-conference interview with Edward Snowden [9]. It’s unusually long by TED standards but definitely worth watching.

Tom Meagher (who’s wife was raped and murdered two years ago) wrote an insightful article about rape culture [10].

Key Lay (the Victorian Chief Commissioner of Police) wrote a good article encouraging men to act to stop violence against women [11]. It’s particularly noteworthy when a senior police officer speaks out about this given the difficulties women have had in reporting such crimes to police.

Emily Baker wrote an insightful article about the lack of support for soldiers who survive war [12]. A lot of attention and money is spent remembering the soldiers who died in the field but little on those who live suffer afterwards, more soldiers die from suicide than enemy fire.

Daniel Pocock wrote an informative article about the failings of SMS authentication for online banking [13]. While he has good points I think he’s a little extreme. Stopping the least competent attackers is still a significant benefit as most potential attackers aren’t that competent.

Jess Zimmerman wrote an interesting article for Time about the “Not All Men” argument that is a current trend in derailing discussions about the treatment of women [14].

The Belle Jar has an insightful article “Why Won’t You Educate Me About Feminism” about some ways that men pretend to care about the treatment of women [15].

Jon Evans wrote an article for Tech Crunch about the “Honywell Bubble Count” measure of diversity in people you follow on social media [16]. Currently on Twitter I follow 57 accounts of which 15 are companies and organisations, so I follow 42 people. I follow 13 women 31%, for a visible minority group other than my own it’s 2/42 or 5%, for people who live in other countries I think it’s 8/42 (although it’s difficult to determine where some people live) which is 19%. So my Honywell number is 55.

The Top Stocks forum has an interesting post by a Coal Seam Gas (CSG) worker [17]. It seems that CSG is even worse than I thought.

Ashe Dryden wrote an informative post for Model View Culture about the backlash that members of minority groups (primarily women) receive when they speak out [18].

Autism and the Treatment of Women Again

Background

I’ve previously written about the claim that people use Autism as an excuse for bad behavior [1]. In summary it doesn’t and such claims instead lead to people not being assessed for Autism.

I’ve also previously written about empathy and Autism in the context of discussions about conference sexual harassment [2]. The main point is that anyone who’s going to blame “empathy disorders” for the widespread mistreatment of women in society and divert the subject from the actions of average men to men in minority groups isn’t demonstrating empathy.

Discussions of the actions of average men are so often derailed to cover Autism that the Geek Feminism Wiki has a page about the issue of blaming Autism [3].

The Latest Issue

Last year Shanley Kane wrote an informative article for Medium titled “What Can Men Do” about the treatment of women in the IT industry [4]. It’s a good article, I recommend reading it. As an aside @shanley’s twitter feed is worth reading [5].

In response to Shanley’s article Jeff Atwood wrote an article of the same title this year which covered lots of other things [6]. He writes about Autism but doesn’t seem to realise that officially Asperger Syndrome is now Autism according to DSM-V (they decided that separate diagnosis of Autism, Asperger Syndrome, and PDD-NOS were too difficult and merged them). Asperger Syndrome is now a term that refers to historic issues (IE research that was published before DSM-V) and slang use.

Gender and the Autism Spectrum

Jeff claims that “autism skews heavily towards males at a 4:1 ratio” and cites the Epidemiology of Autism Wikipedia page as a reference. Firstly that page isn’t a great reference, I fixed one major error (which was obviously wrong to anyone who knows anything about Autism and also contradicted the cited reference) in the first section while writing this post.

The Wikipedia page cites a PDF about the Epidemiology of Autism that claims the 4.3:1 ratio of boys to girls [7]. However that PDF is a summary of other articles and the one which originated the 4.3:1 claim is behind a paywall. One thing that is worth noting in the PDF is that the section containing the 4.3:1 claim also references claims about correlations between race and Autism and studies contradicting such claims – it notes the possibility of “ascertainment bias”. I think that anyone who reads that section should immediately consider the possibility of ascertainment bias in regard to the gender ratio.

Most people who are diagnosed with Autism are diagnosed as children. An Autism diagnosis of a child is quite subjective, an important part is an IQ test (where the psychologist interprets the intent of the child in the many cases where answers aren’t clear) to compare social skills with IQ. So whether a child is diagnosed is determined by the psychologist’s impression of the child’s IQ vs the impression of their social skills.

Whether a child is even taken for assessment depends on whether they act in a way that’s considered to be obviously different. Any child who is suspected of being on the Autism Spectrum will be compared other children who have been diagnosed (IE mostly boys) and this will probably increase the probability that a boy will be assessed. So an Aspie girl might not be assessed because she acts like other Aspie girls not like the Aspie boys her parents and teachers have seen.

The way kids act is not solely determined by neuro-type. Our society expects and encourages boys to be louder than girls and take longer and more frequent turns to speak, this is so widespread that I don’t think it’s possible for parents to avoid it if their kids are exposed to the outside world. Because of this boys who would be diagnosed with Asperger Syndrome by DSM-IV tend to act in ways that are obviously different from other kids. While the combination of Autism and the the social expectations on girls tends to result in girls who are quiet, shy, and apologetic. The fact that girls are less obviously different and that their differences cause fewer difficulties for parents and teachers makes them less likely to be assessed. Note that the differences in behavior of boys and girls who have been diagnosed is noted by the professionals (and was discussed at a conference on AsperGirls that my wife attended) while the idea that this affects assessment rates is my theory.

Jeff also cites the book “The Essential Difference: Male And Female Brains And The Truth About Autism” by Professor Simon Baron-Cohen (who’s (in)famous for his “Extreme Male Brain” theory). The first thing to note about the “Extreme Male Brain” theory are that it depends almost entirely on the 4.3:1 ratio of males to females on the Autism Spectrum (which is dubious as I noted above). The only other evidence in support of it is subjective studies of children which suffer from the same cultural issues – this is why “double blind” tests should be used whenever possible. The book Delusions of Gender by Cordelia Fine [8] debunks Simon Baron-Cohen’s work among other things. The “look inside” feature of the Amazon page for Delusions of Gender allows you to read about Simon Baron-Cohen’s work [9].

Now even if the “Extreme Male Brain” theory had any merit it would be a really bad idea to cite it (or a book based on it) if you want to make things better for women in the IT industry. Cordelia’s book debunks the science and also shows how such claims about supposed essential difference are taken as exclusionary.

The Problem with Jeff Atwood

Jeff suggests in his post that men should listen to women. Then he and his followers have a huge flame-war with many women over twitter during which which he tweeted “Trying to diversify my follows by following any female voices that engaged me in a civil, constructive way recently“. If you only listen to women who agree with you then that doesn’t really count as listening to women. When you have a stated policy of only listening to women who agree then it seems to be more about limiting what women may feel free to say around you. The Geek Feminism wiki page about the “Tone Argument [10] says the following:

One way in which the tone argument frequently manifests itself is as a call for civility. A way to gauge whether a request for civility is sincere or not is to ask whether the person asking for civility has more power along whatever axes are contextually relevant (see Intersectionality) than the person being called “incivil”, less power, or equal power. Often, people who have the privilege of being listened to and taken seriously level accusations of “incivility” as a silencing tactic, and label as “incivil” any speech or behavior that questions their privilege. For example, some men label any feminist thought or speech as hostile or impolite; there is no way for anybody to question male power or privilege without being called rude or aggressive. Likewise, some white people label any critical discussion of race, particularly when initiated by people of color, as incivil.

Writing about one topic is also a really good idea. A blog post titled “What Can Men Do” should be about things that men can do. Not about Autism, speculation about supposed inherent differences between men and women which are based on bad research, gender diversity in various occupations, etc. Following up a post on “What Can Men Do” with discussion (in blog comments and twitter) about what women should do before they are allowed to join the conversation is ridiculous. Jeff’s blog post says that men should listen to women, excluding women based on the tone argument is gross hypocrisy.

Swearing

Jeff makes a big deal of the fact that Shanley uses some profane language in her tweets. This combines a couple of different ways of silencing women. It’s quite common for women to be held to a high standard of “ladylike” behavior, while men get a free pass on doing the same thing. One example of this is the Geek Feminism article about the results of Sarah Sharp’s request for civility in the Linux kernel community [11]. That’s not an isolated incident, to the best of my recollection in 20+ years my local Linux Users Group has had only one debate about profanity on mailing lists – in that case a woman (who is no longer active in the group) was criticised for using lesser profanity than men used both before and after with no comment (as an experiment I used some gratuitous profanity a couple of weeks later and no-one commented).

There is also a common difference in interpretation of expressions of emotion, when a woman seems angry then she invariably has men tell her to change her approach (even when there are obvious reasons for her anger) while when a man is angry the possibility that other people shouldn’t make him angry will usually be considered.

The issues related to the treatment of women have had a large affect on Shanley’s life and her friend’s lives. It’s quite understandable that she is angry about this. Her use of profanity in tweets seems appropriate to the situation.

Other Links

Newsweek’s “Gentlemen” in Technology article has a section about Jeff [12], it’s interesting to note his history of deleting tweets and editing his post. I presume he will change his post in response to mine and not make any note of the differences.

Jacob Kaplan-Moss wrote a good rebuttal to Jeff’s post [13]. It’s a good article and has some other relevant links that are worth reading.

Swap Breaking SSD

I’ve seen many comments about swap space and SSD claiming that swap will inherently destroy SSD through using too many writes. The latest was in the comments of my post about swap space and SSD performance [1]. Note that I’m not criticising the person who commented on my blog, everyone has heard lots of reports about possible problems that they avoid without analysing them in detail.

The first thing to note is that the quality of flash memory varies a lot, the chips that are used in SSDs for workstation/server use are designed to last while those in USB-flash devices aren’t. I’ve documented my unsuccessful experiments with using USB-flash for the root filesystem of a gateway server [2] (and the flash device that wasn’t used for swap died too).

The real issue when determining whether swap will break your SSD is the amount of writes. While swapping can do a lot of writing quickly that usually doesn’t happen unless something has gone wrong. The workstation that I’m currently using has writes to the root fileystem outnumbering writes to swap by a factor of 130:1 (by volume of data written). On other days I’ve seen it as low as 42:1, in either case it’s writes to the root filesystem (which is BTRFS and includes /home etc) that will break the SSD if anything. For some other workstations I run I see ratios of 201:1 (that’s with 8G of RAM), 57:1, and 23:1. In a quick search I couldn’t find a single system I run where even 10% of disk writes were attributed to swap. This really isn’t surprising given that adding RAM is a cheap way to improve the performance of most systems. If a SSD didn’t do any write leveling (as is rumored to be the case with cheap USB flash devices) then swap use might still cause a problem because of the number of writes in a small area, but if that was the case then filesystem journals and other fixed data structures would be more likely to cause a problem – and any swap based breakage would break swap not the root filesystem (although if swap was the first partition then it might also break the MBR).

Of the workstations that are convenient to inspect the one with the most writes to the root filesystem and swap space (IE everything on /dev/sda) had 128G written per day for 1.2 days of uptime, but that involved running a filesystem balance and some torrent downloads (not the typical use). Among the two systems which had been running for more than 48 hours with typical use the most writes was 24G in a day. If a SSD can sustain 10,000 writes per block (which is smaller than quoted by most flash manufacturers nowadays) and has perfect wear leveling (which is unlikely) then the system with a 120G SSD and 128G written in a day could continue like that for almost 10,000 days or 27 years – much longer than storage is expected to work or be useful. So for workstation use (where even 24G of writes per day probably counts as heavy use) a 120G SSD that can sustain 10,000 writes per block shouldn’t be at great risk of wearing out.

Conclusion

I believe that swap is much less likely to break SSDs than regular file access on every system with a reasonable amount of RAM. For systems which don’t have enough RAM you probably want the speed of SSD for swap space anyway in spite of the risks.

If wear leveling works as designed and the 10,000+ writes per block claims are accurate then SSDs will massively outlast their useful life. Long before they wear out they should be too small, too slow, and probably not compatible. 26 years ago I had a 5.25″ full height ST-506 disk in my desktop PC, it wouldn’t physically fit in most systems I own now (unless I removed the DVD drive), there is no possibility of buying a controller (I don’t own a system with an ISA bus), and that disk was too slow and small by today’s standards. A 27yo SSD isn’t going to be useful for anything, even for archive storage it’s no good as no-one has tested long term storage and data could decay before then.

BTRFS Status April 2014

Since my blog post about BTRFS in March [1] not much has changed for me. Until yesterday I was using 3.13 kernels on all my systems and dealing with the occasional kmail index file corruption problem.

Yesterday my main workstation ran out of disk space and went read-only. I started a BTRFS balance which didn’t seem to be doing any good because most of the space was actually in use so I deleted a bunch of snapshots. Then my X session aborted (some problem with KDE or the X server – I’ll never know as logs couldn’t be written to disk). I rebooted the system and had kernel threads go into infinite loops with repeated messages about a lack of response for 22 seconds (I should have photographed the screen). When it got into that state the ALT-Fn keys to change a virtual console sometimes worked but nothing else worked – the terminal usually didn’t respond to input.

To try and stop the kernel from entering an infinite loop on every boot that I used “rootflags=skip_balance” on the kernel command line to stop it from continuing the balance which made the system usable for a little longer, unfortunately the skip_balance mount option doesn’t permanently apply, the kernel will keep trying to balance the filesystem on every mount until a “btrfs balance cancel” operation succeeds. But my attempts to cancel the balance always failed.

When I booted my system with skip_balance it would sometimes free some space from the deleted snapshots, after two good runs I got to 17G free. But after that every time I rebooted it would report another Gig or two free (according to “btrfs filesystem df“) and then hang without committing the changes to disk.

I solved this problem by upgrading my USB rescue image to kernel 3.14 from Debian/Experimental and mounting the filesystem from the rescue image. After letting kernel 3.14 work on the filesystem for a while it was in a stage where I could use it with kernel 3.13 and then boot the system normally to upgrade it to kernel 3.14.

I had a minor extra complication due to the fact that I was running “apt-get dist-upgrade” at the time the filesystem went read-only do the dpkg records of which packages were installed were a bit messed up. But that was easy to fix by running a diff against /var/lib/dpkg/info on a recent snapshot. In retrospect I should have copied from an old snapshot of the root filesystem, but I fixed the problems faster than I could think of better ways to fix them.

When running a balance the system had a peak IO rate of about 30MB/s reads and 30MB/s writes. That compares to the maximum contiguous file IO speed of 260MB/s for reads and 320MB/s for writes. During that time it had about 50% CPU time used for my Q8400 quad-core CPU. So far the only tasks that I do regularly which have CPU speed as a significant bottleneck are BTRFS filesystem balancing and recoding MP4 files. Compiling hasn’t been an issue because recently I haven’t been compiling many programs that are particularly big.

Lessons Learned

I should photograph the screen regularly when doing things that won’t be logged, those kernel error messages might have been useful to me or someone else.

The fact that the only kernel that runs BTRFS the way I need comes from the Experimental repository in Debian stands in contrast to the recent kernel patch that stops describing BTRFS as experimental. While I have a high opinion of the people who provide support for the kernel in commercial distributions and their ability to back-port fixes from newer kernels I’m concerned about their decision to support BTRFS. I’m also dubious about whether we can offer BTRFS support in Debian/Jessie (the next version of Debian) without a significant warning. OTOH if you find yourself with a BTRFS system that isn’t working well you could always hire me to fix it. I accept payment via Paypal, bank transfer, or Bitcoin. If you want to pay me in Grange then I assure you I will never forget about it. ;)

I thought that I wouldn’t have CPU speed issues when I started using the AMD64 architecture, for most tasks that’s been the case. But for systems for which storage is important I’ll look at getting faster CPUs because of BTRFS. Using faster CPUs for storage isn’t that uncommon (I used to work for SGI and dealt with some significant CPU power used for file serving), but needing a fast quad-core CPU to drive a single SSD is a little disappointing. While recovery from file system corner cases isn’t going to be particularly common it’s something that you want completed quickly, for personal systems you want to be doing something else and for work systems you don’t want down-time.

The BTRFS problems with running out of disk space are really serious. It seems that even workstations used at home can’t survive without monitoring. For any other filesystem used at home you can just let it get full and then delete stuff.

Include “rootflags=skip_balance” in the boot loader configuration for every system with a BTRFS root filesystem and in the /etc/fstab for every non-root BTRFS filesystem. I haven’t yet encountered a single situation where continuing the balance did any good or when it didn’t do any harm.

Sociological Images 2014

White Trash

The above poster was on a bridge pylon in Flinders St in 2012. It’s interesting to see what the Fringe Festival people consider to be associated with “white trash”. They claim homophobia is a “white trash” thing however lower class people have little political power and the fact that we still don’t have marriage equality in Australia is clear evidence that homophobia is prevalent among powerful people.

Toys vs Fairies

Fairies look pretty while boys toys do things

I took the above photo at Costco in 2012. I think it’s worth noting the way that the Disney Fairies (all female and marketed to a female audience) are standing around looking pretty while the Toy Story characters (mostly male and marketed to a male audience) are running out to do things. Having those items side by side on the shelf was a clear example of a trend in toys towards girls being encouraged to be passive while boys are doing things. The Toy Story pack has one female character, so it could be interpreted as being aimed at both boys and girls. But even that interpretation doesn’t remove the clear gender difference.

It seems ironic to me that the descriptions on the boxes are “Read, Play, and Listen” for the Toy Story pack and “Read, Play, and Colour” on the Fairies pack. Colouring is more active than listening so the pictures don’t match the contents.

Make Up vs Tools

Girls chocolate is make-up and boys chocolate is tools

I took the above photo in an Aldi store in early 2013, today I was in Aldi and noticed that the same chocolate is still on sale. A clear and pointless gender difference. Rumor has it that some of the gender difference in kids clothing is so that a child can’t wear the clothes of an older sibling of different gender, but chocolate only gets eaten once so there is no reason for this.

Oath

The above poster was inside the male toilet at Melbourne University in 2013. It would probably be good to have something like that on display all the time instead of just for one event.

Locks

Locks with inscriptions on a bridge on the Yarra River in Melbourne

I took the above picture early this year, it shows hundreds of padlocks attached to a bridge across the Yarra River in Melbourne. Each padlock has a message written or inscribed in it, mostly declarations of love. I first noticed this last year, I’m not sure how long it’s been up. There was nothing formal about this (no signs about it), people just see it and decide that they want to add to it. I guess that the council cuts some of them off periodically as the number of locks doesn’t seem to be increasing much in recent times.

It would be interesting to do some research into how many locks are needed to start one of these. It would also be interesting to discover whether the nature of the inscriptions determines the speed at which it takes off, would a bunch of padlocks with messages like “I Love Linux” inspire others as well as messages declaring love for random people? All that is required is some old locks and an engraving tool.

I wonder what the social norm might be regarding messing with those locks. If I was to use those padlocks to practice the sport of lock-picking (which I learned when in Amsterdam) I wonder whether random bystanders would try to discourage me. It seems likely that picking the locks and taking them away would get a negative reaction but I wonder whether picking them one at a time and replacing them (or maybe moving them to another wire) would get a reaction.

Blackface for Schoolkids

teachers choice blackface and yellowface masks

A craft shop at the Highpoint shopping center in Melbourne is selling “Teacher’s Choice” brand “Multicultural Face Masks”. “Multicultural” is a well regarded term in education, teaching children about other cultures is a good concept but can be implemented really badly. When I was in high school the subject “Social Studies” seemed to have an approach of “look how weird people are in other places” instead of teaching the kids anything useful.

Sociological Images has an informative article on the Australian Hey Hey it’s Saturday blackface incident in 2009 [1].

The idea of these masks seems to involve students dressing up as caricatures of other races. The mask which looks like someone’s idea of a Geisha is an even bigger WTF, mixing what the package calls “culture” (really race) with sex work. When I visited Tokyo I got the impression that “French maids” fill a similar niche to Geisha for younger Japanese men and the “maid cafe” thing is really popular there. I think it’s interesting to consider the way that a French maid costume is regarded differently to a Geisha costume. I expect that “Teacher’s Choice” doesn’t sell French maid costumes.

Delicious Cow

picture of a bovine named Delicious

Usually meat is advertised in a way that minimises the connection to living animals. Often adverts just show cuts of meat and don’t make any mention of animals and when animals are shown they are in the distance. The above picture was on the wall at a Grill’d burger restaurant in Point Cook. It shows a bovine (looks like a bull even though I believe that cows are the ones that are usually eaten) with a name-tag identifying it as “Delicious”. The name tag personalises the animal which is an uncommon thing to do when parts of an animal are going to be eaten.

Of the animals that are commonly eaten it seems that the general trend is to only show fish as complete live animals, presumably because people can identify with mammals such as cattle in a way that they can’t identify with fish. Fish are also the only complete animals that are shown dead, adverts for fish that are sold as parts (EG salmon and tuna) often show complete dead fish. But I’ve never seen a meat advert that shows a complete dead cow or sheep.

Sociological Images 2012

In 2011 I wrote a post that was inspired by the Sociological Images blog [1]. After some delay here I’ve written another one. I plan to continue documenting such things.

Playground

gender segregated playground in 1918

In 2011 I photographed a plaque at Flagstaff Gardens in Melbourne. It shows a picture of the playground in 1918 with segregated boys and girls sections. It’s interesting that the only difference between the two sections is that the boys have horizontal bars and a trapeze. Do they still have gender segregated playgrounds anywhere in Australia? If so what is the difference in the sections?

Aborigines

The Android game Paradise Island [2] has a feature where you are supposed to stop Aborigines from stealing, it plays on the old racist stereotypes about Aborigines which are used to hide the historical record that it’s always been white people stealing from the people that they colonise.

Angry face icons over AboriginesAborigines described as thieves

There is also another picture showing the grass skirts. Nowadays the vast majority of Aborigines don’t wear such clothing, the only time they do is when doing some sort of historical presentation for tourists.

I took those pictures in 2012, but apparently the game hasn’t changed much since then.

Lemonade

lemonade flavored fizzy drink

Is lemonade a drink or a flavour? Most people at the party where I took the above photo regard lemonade as a drink and found the phrase “Lemonade Flavoured Soft Drink” strange when it was pointed out to them. Incidentally the drink on the right tastes a bit like the US version of lemonade (which is quite different from the Australian version). For US readers, the convention in Australia is that “lemonade” has no flavor of lemons.

Not Sweet

maybe gender queer people on bikes

In 2012 an apple cider company made a huge advertising campaign featuring people who might be gender queer, above is a picture of a bus stop poster and there were also TV ads. The adverts gave no information at all about what the drink might taste like apart from not being “as sweet as you think”. So it’s basically an advertising campaign with no substance other than a joke about people who don’t conform to gender norms.

Also it should be noted that some women naturally grow beards and have religious reasons for not shaving [3].

Episode 2 of the TV documentary series “Am I Normal” has an interesting interview of a woman with a beard.

Revolution

communist revolution Schweppes drinks

A violent political revolution is usually a bad thing, using such revolutions to advertise sugar drinks seems like a bad idea. But it seems particularly interesting to note the different attitudes to such things in various countries. In 2012 Schweppes in Australia ran a marketing campaign based on imagery related to a Communist revolution (the above photo was taken at Southern Cross station in Melbourne), I presume that Schweppes in the US didn’t run that campaign. I wonder whether global media will stop such things, presumably that campaign has the potential to do more harm in the US than good in Australia.

Racist Penis Size Joke at Southbank

racist advert in Southbank paper

The above advert was in a free newspaper at Southbank in 2012. Mini Movers thought that this advert was a good idea and so did the management of Southbank who approved the advert for their paper. Australia is so racist that people don’t even realise they are being racist.

Swap Space and SSD

In 2007 I wrote a blog post about swap space [1]. The main point of that article was to debunk the claim that Linux needs a swap space twice as large as main memory (in summary such advice is based on BSD Unix systems and has never applied to Linux and that most storage devices aren’t fast enough for large swap). That post was picked up by Barrapunto (Spanish Slashdot) and became one of the most popular posts I’ve written [2].

In the past 7 years things have changed. Back then 2G of RAM was still a reasonable amount and 4G was a lot for a desktop system or laptop. Now there are even phones with 3G of RAM, 4G is about the minimum for any new desktop or laptop, and desktop/laptop systems with 16G aren’t that uncommon. Another significant development is the use of SSDs which dramatically improve speed for some operations (mainly seeks).

As SATA SSDs for desktop use start at about $110 I think it’s safe to assume that everyone who wants a fast desktop system has one. As a major limiting factor in swap use is the seek performance of the storage the use of SSDs should allow greater swap use. My main desktop system has 4G of RAM (it’s an older Intel 64bit system and doesn’t support more) and has 4G of swap space on an Intel SSD. My work flow involves having dozens of Chromium tabs open at the same time, usually performance starts to drop when I get to about 3.5G of swap in use.

While SSD generally has excellent random IO performance the contiguous IO performance often isn’t much better than hard drives. My Intel SSDSC2CT12 300i 128G can do over 5000 random seeks per second but for sustained contiguous filesystem IO can only do 225M/s for writes and 274M/s for reads. The contiguous IO performance is less than twice as good as a cheap 3TB SATA disk. It also seems that the performance of SSDs aren’t as consistent as that of hard drives, when a hard drive delivers a certain level of performance then it can generally do so 24*7 but a SSD will sometimes reduce performance to move blocks around (the erase block size is usually a lot larger than the filesystem block size).

It’s obvious that SSDs allow significantly better swap performance and therefore make it viable to run a system with more swap in use but that doesn’t allow unlimited swap. Even when using programs like Chromium (which seems to allocate huge amounts of RAM that aren’t used much) it doesn’t seem viable to have swap be much bigger than 4G on a system with 4G of RAM. Now I could buy another SSD and use two swap spaces for double the overall throughput (which would still be cheaper than buying a PC that supports 8G of RAM), but that still wouldn’t solve all problems.

One issue I have been having on occasion is BTRFS failing to allocate kernel memory when managing snapshots. I’m not sure if this would be solved by adding more RAM as it could be an issue of RAM fragmentation – I won’t file a bug report about this until some of the other BTRFS bugs are fixed. Another problem I have had is when running Minecraft the driver for my ATI video card fails to allocate contiguous kernel memory, this is one that almost certainly wouldn’t be solved by just adding more swap – but might be solved if I tweaked the kernel to be more aggressive about swapping out data.

In 2007 when using hard drives for swap I found that the maximum space that could be used with reasonable performance for typical desktop operations was something less than 2G. Now with a SSD the limit for usable swap seems to be something like 4G on a system with 4G of RAM. On a system with only 2G of RAM that might allow the system to be usable with swap being twice as large as RAM, but with the amounts of RAM in modern PCs it seems that even SSD doesn’t allow using a swap space larger than RAM for typical use unless it’s being used for hibernation.

Conclusion

It seems that nothing has significantly changed in the last 7 years. We have more RAM, faster storage, and applications that are more memory hungry. The end result is that swap still isn’t very usable for anything other than hibernation if it’s larger than RAM.

It would be nice if application developers could stop increasing the use of RAM. Currently it seems that the RAM requirements for Linux desktop use are about 3 years behind the RAM requirements for Windows. This is convenient as a PC is fully depreciated according to the tax office after 3 years. This makes it easy to get 3 year old PCs cheaply (or sometimes for free as rubbish) which work really well for Linux. But it would be nice if we could be 4 or 5 years behind Windows in terms of hardware requirements to reduce the hardware requirements for Linux users even further.

Phone Based Lectures

Early this month at a LUV meeting I gave a talk with only my mobile phone to store notes. I used Google Keep to write the notes as it’s one of the easiest ways of writing a note on a PC and quickly transferring it to a phone – if I keep doing this I will find some suitable free software for this task. Owncloud seems promising [1], but at the moment I’m more concerned with people issues than software.

Over the years I’ve experimented with different ways of presenting lectures. I’m now working with the theory that presenting the same data twice (by speaking and text on a projector) distracts the audience and decreases learning.

Editing and Viewing Notes

Google Keep is adequate for maintaining notes, it’s based on notes that are a list of items (like a shopping list) which is fine for lecture notes. It probably has lots of other functionality but I don’t care much about that. Keep is really fast at updating notes, I can commit a change on my laptop and have it visible on my phone in a few seconds over 3G.

Most of the lectures that I’ve given have involved notes on a laptop. My first laptop was a Thinkpad 385XD with a 12.1″ display and all my subsequent laptops have had a bigger screen. When a laptop with a 12″ or larger screen is on a lectern I can see the notes at a glance without having to lean forward when 15 or fewer lines of text are displayed on the screen. 15 lines of text is about the maximum that can be displayed on a slide for the audience to read and with the width of a computer display or projector is enough for a reasonable quantity of text.

When I run Keep on my Galaxy Note 2 it displays about 20 rather short lines of text in a “portrait” orientation (5 points for a lecture) and 11 slightly longer lines in a “landscape” orientation (4 points). In both cases the amount of text displayed on a screen is less than that with a laptop while the font is a lot smaller. My aim is to use free software for everything, so when I replace Keep with Owncloud (or something similar) I will probably have some options for changing the font size. But that means having less than 5 points displayed on screen at a time and thus a change in the way I present my talks (I generally change the order of points based on how well the audience seem to get the concepts so seeing multiple points on screen at the same time is a benefit).

The Samsung Galaxy Note 2 has a 5.5″ display which is one of the largest displays available in a phone. The Sony Xperia X Ultra is one of the few larger phones with a 6.44″ display – that’s a large phone but still not nearly large enough to have more than a few points on screen with a font readable by someone with average vision while it rests on a lectern.

The most obvious solution to the problem of text size is to use a tablet. Modern 10″ tablets have resolutions ranging from 1920*1080 to 2560*1600 and should be more readable than the Thinkpad I used in 1998 which had a 12″ 800*600 display. Another possibility that I’m considering is using an old phone, a Samsung Galaxy S weighs 118 to 155 grams and is easier to hold up than a Galaxy Note 2 which weighs 180g. While 60g doesn’t seem like much difference if I’m going to hold a phone in front of me for most of an hour the smaller and lighter phone will be easier and maybe less distracting for the audience.

Distributing URLs

When I give a talk I often want to share the addresses of relevant web sites with the audience. When I give a talk with the traditional style lecture notes I just put the URLs on the final page (sometimes using tinyurl.com) for people to copy during question time. When I use a phone I have to find another way.

I did a test with QR code recognition and found that a code that takes up most of the width of the screen of my Galaxy Note 2 can be recognised by a Galaxy S at a distance of 50cm. If I ran the same software on a 10″ tablet then it would probably be readable at a distance of a meter, if I had the QR code take up the entire screen on a tablet it might be readable at 1.5m away, so it doesn’t seem plausible to hold up a tablet and allow even the first few rows of the audience to decode a QR code. Even if newer phones have better photographic capabilities than the Galaxy S that I had available for testing there are still lots of people using old phones who I want to support. I think that if QR codes are to be used they have to be usable by at least the first three rows of the audience for a small audience of maybe 50 people as that would allow everyone who’s interested to quickly get in range and scan the code at the end.

Chris Samuel has a photo (taken at the same meeting) showing how a QR code from a phone could be distributed to a room [2]. But that won’t work for all rooms.

One option is to just have the QR code on my phone and allow audience members to scan it after the lecture. As most members of the audience won’t want the URLs it should be possible for the interested people to queue up to scan the QR code(s).

Another possibility I’m considering is to use a temporary post on my documents blog (which isn’t syndicated) for URLs. The WordPress client for Android works reasonably well so I could edit the URL list at any time. That would work reasonably well for talks that have lots of URLs – which is quite rare for me.

A final option is to use Twitter, at the end of a talk I could just tweet the URLs with suitable descriptions. A good portion of the Tweets that I have written is URLs for web sites that I find interesting so this isn’t a change. This is probably the easiest option, but with the usual caveat of using a proprietary service as an interim measure until I get a free software alternative working.

Any suggestions?

Please comment if you have any ideas about ways of addressing these issues.

Also please let me know if anyone is working on a distributed Twitter replacement. Please note that anything which doesn’t support followers on multiple servers and re-tweets and tweeting to users on other servers isn’t useful in this regard.

Replacement Credit Cards and Bank Failings

I just read an interesting article by Brian Krebs about the difficulty in replacing credit cards [1].

The main reason that credit cards need to be replaced is that they have a single set of numbers that is used for all transactions. If credit cards were designed properly for modern use (IE since 2000 or so) they would act as a smart-card as the recommended way of payment in store. Currently I have a Mastercard and an Amex card, the Mastercard (issued about a year ago) has no smart-card feature and as Amex is rejected by most stores I’ve never had a chance to use the smart-card part of a credit card. If all American credit cards had a smart card feature which was recommended by store staff then the problems that Brian documents would never have happened, the attacks on Target and other companies would have got very few card numbers and the companies that make cards wouldn’t have a backlog of orders.

If a bank was to buy USB smart-card readers for all their customers then they would be very cheap (the hardware is simple and therefore the unit price would be low if purchasing a few million). As banks are greedy they could make customers pay for the readers and even make a profit on them. Then for online banking at home the user could use a code that’s generated for the transaction in question and thus avoid most forms of online banking fraud – the only possible form of fraud would be to make a $10 payment to a legitimate company become a $1000 payment to a fraudster but that’s a lot more work and a lot less money than other forms of credit card fraud.

A significant portion of all credit card transactions performed over the phone are made from the customer’s home. Of the ones that aren’t made from home a significant portion would be done from a hotel, office, or other place where a smart-card reader might be conveniently used to generate a one-time code for the transaction.

The main remaining problem seems to be the use of raised numbers. Many years ago it used to be common for credit card purchases to involve using some form of “carbon paper” and the raised numbers made an impression on the credit card transfer form. I don’t recall ever using a credit card in that way, I’ve only had credit cards for about 18 years and my memories of the raised numbers on credit cards being used to make an impression on paper only involve watching my parents pay when I was young. It seems likely that someone who likes paying by credit card and does so at small companies might have some recent experience of “carbon paper” payment, but anyone who prefers EFTPOS and cash probably wouldn’t.

If the credit card number (used for phone and Internet transactions in situations where a smart card reader isn’t available) wasn’t raised then it could be changed by posting a sticker with a new number that the customer could apply to their card. The customer wouldn’t even need to wait for the post before their card could be used again as the smart card part would never be invalid. The magnetic stripe on the card could be changed at any bank and there’s no reason why an ATM couldn’t identify a card by it’s smart-card and then write a new magnetic stripe automatically.

These problems aren’t difficult to solve. The amounts of effort and money involved in solving them are tiny compared to the costs of cleaning up the mess from a major breach such as the recent Target one, the main thing that needs to be done to implement my ideas is widespread support of smart-card readers and that seems to have been done already. It seems to me that the main problem is the incompetence of financial institutions. I think the fact that there’s no serious competitor to Paypal is one of the many obvious proofs of the incompetence of financial companies.

The effective operation of banks is essential to the economy and the savings of individuals are guaranteed by the government (so when a bank fails a lot of tax money will be used). It seems to me that we need to have national banks run by governments with the aim of financial security. Even if banks were good at their business (and they obviously aren’t) I don’t think that they can be trusted with it, an organisation that’s “too big to fail” is too big to lack accountability to the citizens.

Finding Corrupt Files that cause a Kernel Error

There is a BTRFS bug in kernel 3.13 which is triggered by Kmail and causes Kmail index files to become seriously corrupt. Another bug in BTRFS causes a kernel GPF when an application tries to read such a file, that results in a SEGV being sent to the application. After that the kernel ceases to operate correctly for any files on that filesystem and no command other than “reboot -nf” (hard reset without flushing write-back caches) can be relied on to work correctly. The second bug should be fixed in Linux 3.14, I’m not sure about the first one.

In the mean time I have several systems running Kmail on BTRFS which have this problem.

(strace tar cf – . |cat > /dev/null) 2>&1|tail

To discover which file is corrupt I run the above command after a reboot. Below is a sample of the typical output of that command which shows that the file named “.trash.index” is corrupt. After discovering the file name I run “reboot -nf” and then delete the file (the file can be deleted on a clean system but not after a kernel GPF). Of recent times I’ve been doing this about once every 5 days, so on average each Kmail/BTRFS system has been getting disk corruption every two weeks. Fortunately every time the corruption has been on an index file so I don’t need to restore from backups.

newfstatat(4, ".trash.index", {st_mode=S_IFREG|0600, st_size=33, …}, AT_SYMLINK_NOFOLLOW) = 0
openat(4, ".trash.index", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_NOFOLLOW|O_CLOEXEC) = 5
fstat(5, {st_mode=S_IFREG|0600, st_size=33, …}) = 0
read(5,  <unfinished …>
+++ killed by SIGSEGV +++