lkml.org 
[lkml]   [2008]   [Apr]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/8][for -mm] mem_notify v6
On Fri, Apr 18, 2008 at 3:07 AM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:

> I investigated again and found 2 problem in your test program.
>
> 1. text segment isn't locked.
>
> if strong memory pressure happned, kernel may drop program text region.
> then your test program suddenly slow down.
>
> please use mlockall(MCL_CURRENT) before large buffer allocation.

Using mlock does enable the program to respond faster (and/or the
kernel doesn't have to find memory to fault the page in) and solves
the problem for this simple test program. I think we're thinking of
the solution in two different ways: you want the program to react more
quickly or be "nicer", and I want the kernel to give notification
early enough to allow time for things that can (and do) happen when
things aren't so nice. I realize that in extreme circumstances oom may
be unavoidable, but a threshold-based notification, in addition to the
current /dev/mem_notify mechanism, would help avoid extreme
circumstances. I'm going to look into doing this.

> 2. repeat open/close to /proc/meminfo.
>
> in the fact, open(2) system call use a bit memory.
> if call open(2) in strong memory pressure, doesn't return until
> memory freed enough.
> thus, it cause slow down your program sometimes.

This should be fine; I intentionally do the open/read/write/close
after freeing memory.

> attached changed test program :)
> it works well on my test environment.

I made your changes to my program (I'm using clone since I don't have
a pthreads library on my device, and I left PAGESIZE at 4K instead of
64K), and having memory locked does avoid oom in this case, but
unfortunately I don't think it's a general solution that will work
everywhere in my system. (Although I'm going to try it.)

Thanks,
.tom


\
 
 \ /
  Last update: 2008-04-21 22:35    [W:0.073 / U:0.192 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site