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SubjectRe: [RFC][PATCH] oom_kill: avoid depends on total_vm and use real RSS/swap value for oom_score (Re: Memory overcommit
On Tue, 27 Oct 2009, KAMEZAWA Hiroyuki wrote:
> Now, oom-killer's score uses mm->total_vm as its base value.
> But, in these days, applications like GUI program tend to use
> much shared libraries and total_vm grows too high even when
> pages are not fully mapped.
>
> For example, running a program "mmap" which allocates 1 GBbytes of
> anonymous memory, oom_score top 10 on system will be..
>
> score PID name
> 89924 3938 mixer_applet2
> 90210 3942 tomboy
> 94753 3936 clock-applet
> 101994 3919 pulseaudio
> 113525 4028 gnome-terminal
> 127340 1 init
> 128177 3871 nautilus
> 151003 11515 bash
> 256944 11653 mmap <-----------------use 1G of anon
> 425561 3829 gnome-session
>
> No one believes gnome-session is more guilty than "mmap".
>
> Instead of total_vm, we should use anon/file/swap usage of a process, I think.
> This patch adds mm->swap_usage and calculate oom_score based on
> anon_rss + file_rss + swap_usage.
> Considering usual applications, this will be much better information than
> total_vm. After this patch, the score on my desktop is
>
> score PID name
> 4033 3176 gnome-panel
> 4077 3113 xinit
> 4526 3190 python
> 4820 3161 gnome-settings-
> 4989 3289 gnome-terminal
> 7105 3271 tomboy
> 8427 3177 nautilus
> 17549 3140 gnome-session
> 128501 3299 bash
> 256106 3383 mmap
>
> This order is not bad, I think.
>
> Note: This adss new counter...then new cost is added.

I've often thought we ought to supply such a swap_usage statistic;
and show it in /proc/pid/statsomething, presumably VmSwap in
/proc/pid/status, even an additional field on the end of statm.

A slight new cost, yes: doesn't matter at the swapping end, but
would slightly impact fork and exit - I do hope we can afford it,
because I think it should have been available all along.

I've not checked your patch in detail; but I do agree that basing
OOM (physical memory) decisions on total_vm (virtual memory) has
seemed weird, so it's well worth trying this approach. Whether swap
should be included along with rss isn't quite clear to me: I'm not
saying you're wrong, not at all, just that it's not quite obvious.

I've several observations to make about bad OOM kill decisions,
but it's probably better that I make them in the original
"Memory overcommit" thread, rather than divert this thread.

Hugh


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