@LaureenH you know, some people accuse *me* of using too many acronyms. in reply to LaureenH #

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Twitter Updates for 2010-03-11

In case of flooding,
all animals find sexy partner
and wait here for boat.

Stencil, Minderbroederstraat, Leuven, 2010

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Noah’s Ark Gathering Point

My contract with my hosting provider is expiring around March 20th, so crypticide.com – my blog and e-mail – will likely drop off the net for a few days from that point.

I have an alternative in planning, but I am time-poor for implementation at the moment.

Folks who need to mail me should use my gmail.com address.

Thanks.

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Advance Notice: crypticide.com extended outage ~ March 20 onward

#iplayer says "Don't forget, to watch TV online as it's being broadcast, you still need a TV licence" – so, time-shifted = unencumbered? #

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Twitter Updates for 2010-03-10

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Twitter Updates for 2010-03-09

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Twitter Updates for 2010-03-07

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Twitter Updates for 2010-03-05

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Twitter Updates for 2010-03-04

The main problems were:

• The “shoulders” on the main bag opening, presumably meant to provide some structure to the bag when you pack-out the body, but actually preventing you from putting anything large into the bag.
• The geometry of the front flap, which bulges curiously when stuffed with items, and seems generally to rest on-top-of (rather than covering) the bag’s body.

Example of the S-bag suffering bag-bloat:

This finally got to the point of vexing me, so I started to look for an alternative:

• the NEW brompton s-bag
• the brompton c-bag
• the NEW brompton t-bag (formerly “touring” pannier)
• the brompton o-bag (ortlieb)
• something else

This led to a bunch of research and decisions; my eventual decisions were:

• new S-bag? alas it’s great for a light day-trip but still awkward and not big enough for my stuff; I like the s-bag style yellow lining, though.
• the C-bag? this was a really strong contender, not least because @bartbl has got one and i’ve been able to see it close-up; the yellow lining is a great idea, the materials good… but the waterproof zips worry me (i’ve seen things like that snag themselves closed, before) and there is an overall “chunkiness” to the materials and strap, which i didn’t really like
• the t-bag? i also have a friend (@ids) who has one of these; they are huge and expandable, but the weird bulges, puffy netting and fabric roll-top have something of the fetish boudoir about them. Plus, I don’t know if it’s fair but to me the design smacks of “I’m going to get rained-upon and then take an age to dry-off, and I’ll be dripping on the floor for ages”.
• and finally, the o-bag? Stupid, stupid amounts of money, and not particularly larger than the S-bag.

So I was stuck.

I found a couple of fabulously useful reviews of the c-bag on the net, mentioning the Carradice City Folder bag in the process. Chris Rust’s review of the City Folder bag sounded pretty rough, and from the pictures I would have agreed with him.

However…

On a Canadian website (URL lost) I found discussion of the Carradice City Folder, including a video, and in the comments a reference to a waterproof version, this led me to the Carradice website, plus a few others, but I hadn’t found any reviews of it.

When next in London I visited Velorution, went through all their Brompton bags, found one of these Carradice Carradry City Folder bags, and bought it on the spot.

To get to the meat of the purchasing decision:

Upsides:

• Large enough, comparible to C-bag
• Reasonable price
• Waterproof and easily wipeable
• Boxy, angular, and semi-rigid, but there’s no impediment to putting stuff into it.
• Interior laptop-compartment large enough to take ancient Thinkpad, let alone Macbook Air.

Downsides:

• No waterproof external pocket for quick access to phone, wallet
• Internal laptop-compartment is permanently fixed; apparently in the non-waterproof version it is removable
• Topmost seam tends to rub on knuckles when carrying through the handles; loosening the bottom velcro helps somewhat.
• The center of the three built-in phone pockets is a bit awkward to use, since it velcros-over to shut the laptop compartment

There are mesh pockets on the CarraDry – two rear, one front, but Carradice’s own people say that these are only fit for light items like gloves and so forth, and I’d agree.

I found this out because I managed to tear one of the mesh pockets from the corner, with the lightest of finger-touches, taking my phone out. The material “ran” and quite a rent appeared, but Carradice and Velorution replaced it immediately and Carradice suspected a manufacturing fault. The replacement bag’s mesh pockets feel rather more coarse and stronger, so I’d agree.

Having experienced two bags I have found a minor random advantage that the first (faulty) bag had over the second: the centre phone-pocket is covered/closed by a strip of double-sided velcro. If that strip has fuzz on one side and hooks on the other then (assuming the bag is put together properly) you’ll have more options for how you close the laptop compartment on top of it.

Unfortunately on my second bag, the strip is fuzzy on both sides, meaning that both the laptop compartment elasticated strip (hooks) and the pocket velcro (also hooks) will not stick together.

This is a small nit, though.

Overall I am very happy with the bag, and certain that I have bought the right bag for me. It’s not my “perfect” brompton bag, but it’s not far off.

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Brompton Carradice CarraDry Waterproof Bag Review

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Twitter Updates for 2010-03-03

@mroesch thank you, marty in reply to mroesch #

must-see for anyone who stays in a hotel: http://bit.ly/aVDmuB #

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Twitter Updates for 2010-03-02

The performance, especially when Firefox is running, or when it’s shutting down, can be dreadful.

I used to wonder why this was; part of it is a thermal issue – when the processor gets hot the operating system (a) clocks it down, so it goes slower and (b) generates lots of idle-loops to try and cool the processor, further degrading power.

If you trawl around the Apple support forums you’ll find a bunch of people talking about “kernel task 100%” which is the operating system either (1) running the aforementioned idle loops, or (2) logging warning messages to (somewhere) about how hot it is, all of a sudden.

Further if you go to the Apple Genius Bar in Regent St, as I recently did for a repair, at least one of the guys there will tell you that the MacBookAir has a known problem which causes the “kernel task 100%” issue, and which can be fixed “by swapping a cable”… though this won’t make your machine any cooler or faster, I suppose it will help performance by not making the machine degrade itself when it gets hot.

But the above is only half of the story.

The other half of the story became evident to me when I started using dtrace (specifically “/usr/bin/iosnoop”) to work out why @adriana872’s similar MacBookAir was being abominably slow; the culprits seemed to be Firefox and Skype, and I was blaming the performance problems on the overheating issues above…

…but I did wonder why it was that “iosnoop” reported “Firefox” to be writing to/from /var/vm/swapfile0 (and others) when it was exiting? That’s right. You’re killing an application, and it’s causing the machine to page virtual memory, really really heavily.

What’s going on?

So I started piecing together what I already knew, and looked at it in terms of what I was trying to achieve. The actual culprit is /sbin/dynamic_pager; in case you haven’t looked at the OSX VM subsystem:

• OSX does not use fixed raw swap partitions; in fact, to get it to use one seems to be such heavy magic that I’ve been put off investigating them. It’s certainly not as easy as poking /etc/fstab.
• Instead, OSX uses dynamically allocated swapfiles on a journalled filesystem, ie: “root”. I don’t know whether there’s an ioctl() that an be used to switch-off journalling for swap devices, but damn this strikes me as a recipe for vile performance, especially on a fragmented disk when the kernel suddenly decides it has to pull-together a few hundred megabytes for scratch space.

So far so bad, but here’s the kicker: the swapfiles are allocated, grown and freed dynamically, too; so the first time you need swap space, it allocates 64M (yes, MEGABYTES) of swap; then the next file is ALSO 64 megabytes, and then the next ones double to 128M, 256M, etc… and when you stop needing that disk space it immediately expends heat and valuable processor time – scarce resources on a netbook-class machine – trying to give you that 256 megabyte file, back.


09:15:14 luther:vm $ ls -la
total 1048576
drwxr-xr-x 6 root wheel 204 1 Mar 09:15 .
drwxr-xr-x 26 root wheel 884 8 Nov 20:47 ..
-rw------- 1 root wheel 67108864 28 Feb 23:28 swapfile0
-rw------- 1 root wheel 67108864 1 Mar 09:19 swapfile1
-rw------- 1 root wheel 134217728 1 Mar 09:19 swapfile2
-rw------- 1 root wheel 268435456 1 Mar 09:19 swapfile3


[firefox explanation elided - see comments, below]

I am certain that somebody thought this exponential-backoff-inspired grow-and-reclaim strategy was a good idea, but it doesn’t make any sense any more. It probably stopped making sense in around 2005 and certainly makes no sense at all today.

The issues are:

• 64M? You Kick-Over Into Paging For A Measly 64 MEGABYTES? Twice? What The Hell Are You Guys Thinking? Firefox Mallocs More Than That For Some Of Its Plugins!
• (less rantingly:) If you’re going to take a bite of the harddisk then at least make it worthwhile. Disk is cheap and it has been for some time.
• And what’s with this dynamic reclamation for small swapfiles?

  It’s bad enough that you’re allocating tiny amounts of virtual memory on-disk but then you insist on shuffling piddling amounts of data between files in order to “release” that disk space back to the user! Frankly if I need 256Mb of disk back then (a) I will empty the trash or (b) I will buy an external disk.

  The OSX strategy makes especially no sense in the Netbook world – We are running with a “small” amount of memory, where “small” = 2Gb, but are likely to be firing-off a small number of very fat applications. What sense is there in creating and reclaiming 64Mb swapfiles when the applications eat 250+Mb apiece?

• UPDATE: worst case scenario: Quit Firefox and you’ll be trying to free (say) a 512Mb file by cloning any live data into one of several smaller files. Fragmentation-Thrash City, on a system that is probably shutting down, or where the user is trying otherwise to shut down the laptop prior to shoving it in his/her briefcase and get the hell out of the office.

Following Brooks’ strategy of “take no half measures” I decided to address this, and last night had the opportunity to re-install my MacBookAir from backup, so I took the chance to do some major surgery.

The steps I have taken to try and bring some sanity to my system, are:

1. The disk is now partitioned in two.

   The first partition (8Gb, near away from the spindle, fast) is called “/Volumes/scratch” and will be used for swapfiles and for temporary files which are not to be backed up. Under SnowLeopard it is no longer possible to make this a UFS filesystem (fast, non-journalled) but at least the partition is unlikely to get fragmented, and it is easily erased/reformatted. I reckon that if you need more than 8G of swap on a MacBookAir then you’re doing something wrong; on bigger systems I will use a bigger partition.

   The second partition is of course the remainder of the disk, and constitutes my “root” / install target.

2. The system should be switchable-off; so I’ve set it so that OSX reverts to default behaviour unless the file “/USE_ALTERNATE_SWAP” exists; if something goes wrong I can remove that file and reboot.
3. The “dynamic_pager” daemon is now wrapped in a launcher-script which enforces a new paging strategy:
   • Every swapfile is to be 1G
   • Do not allocate a swapfile unless less-than 200M of space remains
   • Do not release/reclaim swapfiles unless 2G of swapspace (ie: 2 whole files) are vacant

I’ve wanted to do this for a while; the only thing missing was the method of getting this strategy installed, and I finally found it this morning at a wonderful blog-post on superuser.com – although the guys there are only trying to address the fragmentation issue.

So I wrote the wrapper and installed it (by the same means described in the blog posting) this morning – and I set about trying to thrash my MacBookAir; so far I have gotten it to create 3Gb of swapfiles and it’s not given them back yet – but I don’t mind because that’s what the “scratch” partition is for.

If it gets up to 7Gb and doesn’t give it back, then I will worry, but the manpage for dynamic_pager seems to back up my method.

If you want to see the script I am using, it’s on Google Code.

Links:

• Project Page
• Bug Reports
• Source Code

If you want to try this out, on your head be it. It’s only had 4h of testing, so far.

We can’t fix the Air’s low-speed CPU and we can’t address the heat-retention issue (much) – but we can stop it wasting time fiddling with small changes to virtual memory.

UPDATE: Oh, and to answer the obvious question: performance on the Air seems a lot better; I simultaneously ran up a VirtualBox Ubuntu with 1G of core (ie: half of physmem, + overhead) – plus Firefox with 60 tabs, Safari, Chrome, FinalCutExpress, iPhoto, Tweetdeck and an Adobe AIR updater. It ran slowly, but with almost no beachball-of-death experiences. FinalCut took the longest to launch, but it always does…

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Addressing The Outmoded Swapping And Paging Strategy in OSX?

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Twitter Updates for 2010-03-01

Getting some air on a #Brompton http://bit.ly/cWBIlD #

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Twitter Updates for 2010-02-28

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Twitter Updates for 2010-02-26

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Twitter Updates for 2010-02-25