linux-kernel - Re: [PATCH v3] vm_swappiness=0 should still try to avoid swapping anon memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <e495901c-f2f3-cc85-10a6-0d2944255b19@redhat.com>
Date:   Tue, 19 Apr 2022 19:54:52 -0400
From:   Nico Pache <npache@...hat.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, aquini@...hat.com,
        shakeelb@...gle.com, llong@...hat.com, mhocko@...e.com,
        hakavlad@...ox.lv
Subject: Re: [PATCH v3] vm_swappiness=0 should still try to avoid swapping
 anon memory



On 4/19/22 14:46, Johannes Weiner wrote:
> Hi Nico,
> 
> On Tue, Apr 19, 2022 at 02:11:53PM -0400, Nico Pache wrote:
>> I think its is important to note the issue we are seeing has greatly improved
>> since the initial posting. However we have noticed that the issue is still
>> present (and significantly worse) when cgroupV1 is set.
>>
>> We were initially testing with CgroupV1 and later found that the issue was not
>> as bad in CgroupV2 (but was still an noticeable issue). This is also resulting
>> in the splitting of THPs in the host kernel.
> 
> When swappiness is 0, cgroup limit reclaim has a fixed SCAN_FILE
> branch, so it shouldn't ever look at anon. I'm assuming you're getting
> global reclaim mixed in. Indeed, I think we can try harder not to swap
> for global reclaim if the user asks for that.
> 
> Can you try the below patch?
Sadly this did not fix the V1 case.

I will have to go back through my notes and over the code again to find what
difference between the two may be causing this issue. Im just starting to focus
on this issue again so my memory needs some refreshing of where I was last at.

The good news is that with the current state of upstream the issue of swap
storms tearing down THPs seems to be minimized to sane amount with V2.

My swappiness=0 solution was a minimal approach to regaining the 'avoid swapping
ANON' behavior that was previously there, but as Shakeel pointed out, there may
be something larger at play.

Cheers,
-- Nico