Re: How to controll Buffers to be dilligently reclaimed?

[Cheng Rk <crquan@ymail.com>]

On Thursday, February 12, 2015 11:34 PM, Konstantin Khlebnikov <koct9i@gmail.com> wrote:

>>
>> -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.


in this case, 40GB memory got stuck in Buffers, and 90+% of them are reclaimable (can be verified by vm.drop_caches manual reclaim)
if Buffers are treated same as Cached, why mm.vfs_cache_pressure=10000 (or even I tried up to 1,000,000) can't get Buffers reclaimed early?


I have some oom-killer msgs but were with older kernels, after set vm.overcommit_memory=2, it simply returns -ENOMEM, unable to spawn any new container, why doesn't it even try to reclaim some memory from those 40GB Buffers,



Thanks,

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