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SubjectRe: Long lasting MM bug when swap is smaller than RAM
On Tue, Jun 30, 2009 at 11:58:19AM +0200, Attila Kinali wrote:
> Moin,
>
> There has been a bug back in the 2.4.17 days that is somehow
> triggered by swap being smaller than RAM, which i thought had
> been fixed long ago, reappeared on one of the machines i manage.
>
> <history>
> Back in 2002, i had a few machines, running 2.4.x kernels, which
> i upgraded heavily from some 16-64MB RAM to a couple 100MB
> (changing mainboards at times, but keeping the harddisks).
> Due to the upgrade of RAM, the swap size became a lot smaller
> than RAM size, sometimes not even half as much.
> Under most conditions these machines worked fine, but sometimes,
> they showed a strange behavior: At times, the swap use would grow
> (depending on the machine and its use faster or slower, sometimes
> at 1MB/minute) until it was full. I couldnt figure out what filled
> swap back then, couldnt find any programm that used a lot of memory.
> And even more, the RAM portion that was used as cache and buffers
> was most times still very large, ie it didnt seem like something using
> a lot of memory.
> After swap was full, nothing happend. No programms crashing, no errors
> in the logs, nothing.... Until later (between hours and a few weeks),
> the OOM would suddenly start to kick in and kill applications. This
> time, something would use a lot of memory, but i couldn't figure out
> what. None of the applications running would use more than usual.
> And even killing the usual culprits (Mozilla, X11,...) wouldnt help.
> The only cure was to reboot.
>
> All the machines back then were running Debian, a vanilla kernel,
> and had more RAM than swap and were x86 boxes. Other than that,
> they didnt had much in common. One was a machine with an Adaptec
> 2940UW, others had IDE, one had a K6-III CPU, others were Intel.
> Some had a lot of disk, others very little. Machine usage was
> fileserver, firewall/router, desktop, laptop.
>
> I reported this bug back then but never got an answer, so i used
> the only fix i had available back then: disable swap completely.
> </history>
>
> Now, 7 years later, i have a machine that shows the same behavior.
>
> Some data:
>
> We have a HP DL380 G4 currently running a 2.6.29.4 vanilla kernel,
> compiled for x86 32 bit.
> It was originaly purchased in 2005 with 2GB RAM and a few weeks
> ago upgraded to 6GB (no other changes beside this and a kernel upgrade).
> The machine, being the MPlayer main server, runs a lighttpd, svnserve,
> mailman, postfix, bind. Ie nothing unusual and the applications didn't
> change in the last months (since the update from debian/etch to lenny).
>
> ---
> root@natsuki:/home/attila# uname -a
> Linux natsuki 2.6.29.4 #1 SMP Sun May 31 22:13:21 CEST 2009 i686 GNU/Linux
> root@natsuki:/home/attila# uptime
> 11:41:07 up 29 days, 13:17, 5 users, load average: 0.15, 0.36, 0.54
> root@natsuki:/home/attila# free -m
> total used free shared buffers cached
> Mem: 6023 5919 103 0 415 3873
> -/+ buffers/cache: 1630 4393
> Swap: 3812 879 2932
> ---

Hi Attila,

What's your /proc/meminfo and/or /proc/vmstat contents?
Are you making use of tmpfs, or intel graphics devices with drm?

Thanks,
Fengguang

> I want to point your attention at the fact that the machine has now
> more RAM installed than it previously had RAM+Swap (ie before the upgrade).
> Ie there is no reason it would need to swap out, at least not so much.
>
> What is even more interesting is the amount of swap used over time.
> Sampled every day at 10:00 CEST:
>
> ---
> Date: Wed, 17 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5893 130 0 405 3834
> Swap: 3812 190 3622
>
> Date: Thu, 18 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5793 229 0 340 3939
> Swap: 3812 225 3586
>
> Date: Fri, 19 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5820 203 0 341 3899
> Swap: 3812 275 3536
>
> Date: Sun, 21 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5264 758 0 459 3181
> Swap: 3812 325 3486
>
> Date: Sat, 20 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5761 262 0 348 3865
> Swap: 3812 297 3514
>
> Date: Mon, 22 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5875 147 0 397 3681
> Swap: 3812 353 3458
>
> Date: Tue, 23 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5748 275 0 193 3949
> Swap: 3812 415 3396
>
> Date: Wed, 24 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5779 244 0 176 3924
> Swap: 3812 519 3292
>
> Date: Thu, 25 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5812 210 0 345 3856
> Swap: 3812 611 3200
>
> Date: Fri, 26 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5830 192 0 431 3688
> Swap: 3812 682 3129
>
> Date: Sat, 27 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5697 326 0 442 3621
> Swap: 3812 719 3093
>
> Date: Sun, 28 Jun 2009 10:00:02 +0200 (CEST)
> Mem: 6023 5890 132 0 402 3886
> Swap: 3812 784 3028
>
> Date: Mon, 29 Jun 2009 10:00:01 +0200 (CEST)
> Mem: 6023 5388 635 0 425 3321
> Swap: 3812 826 2985
> ---
>
> As you can see, although memory usage didnt change much over time,
> swap usage increased from 190MB to 826MB in about two weeks.
>
> As i'm pretty much clueless when it commes to how the linux VM works,
> i would appreciate it if someone could give me some pointers on how
> to figure out what causes this bug so that it could be fixed finally.
>
> Thanks a lot in advance
>
> Attila Kinali
>
> --
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