Re: How to controll Buffers to be dilligently reclaimed?

[Konstantin Khlebnikov <koct9i@gmail.com>]

On Fri, Feb 13, 2015 at 3:52 AM, Cheng Rk <crquan@ymail.com> wrote:
>
>
> Hi,
>
> I have a system that application is doing a loop on top of block device,
> (which I think is stupid,)
> as more and more memory goes into Buffers, then applications started
> to get -ENOMEM or be oom-killed later (depends on vm.overcommit_memory setting)
>
>
> In this case, if I do a manual reclaim (echo 3 > /proc/sys/vm/drop_caches)
> I see 90+% of the Buffers is reclaimable, but why it's not reclaimed
> to fullfill applications' memory allocation request?
>
>
>
> -bash-4.2$ sudo losetup -a
> /dev/loop0: [0005]:16512 (/dev/dm-2)
> -bash-4.2$ free -m
>                      total          used         free      shared       buffers     cached
> Mem:             48094        46081         2012              40           40324   2085
> -/+ buffers/cache:             3671        44422
> Swap:             8191                5         8186
>
>
> I've tried sysctl mm.vfs_cache_pressure=10000 but that seems working to Cached
> memory, I wonder is there another sysctl for reclaming Buffers?

AFAIK "Buffers" is just a page-cache of block devices.
>From reclaimer's point of view they have no difference from file page-cache.

Could you post oom-killer log, there should be a lot of numbers
describing memory state.

>
>
> Thanks,
>
> - Derek
>
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