linux-kernel - Re: [PATCH v2] vm_swappiness=0 should still try to avoid swapping anon memory

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Message-ID: <c8de174f-751e-0c2a-3fda-0896e42583e9@redhat.com>
Date:   Mon, 9 Aug 2021 17:19:31 -0400
From:   Nico Pache <npache@...hat.com>
To:     Alexey Avramov <hakavlad@...ox.lv>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, hannes@...xchg.org,
        aquini@...hat.com, shakeelb@...gle.com, llong@...hat.com,
        mhocko@...e.com
Subject: Re: [PATCH v2] vm_swappiness=0 should still try to avoid swapping
 anon memory

On 8/7/21 2:14 AM, Alexey Avramov wrote:
>> vm_swappiness=0 should still try to avoid swapping anon memory
> Swapping with swappiness=0 depends on vm.watermark_scale_factor.
> Decrease vm.watermark_scale_factor to avoid swapping and get OOM,
> and increase vm.watermark_scale_factor to get successful swapping 
> even with swappiness=0.
>
> Maybe I misunderstood you and you are solving some new problem? 

The problem is new; however, the two workloads that are now running into this issue are not new (one is as old as RHEL5).

Sorry the issue was attributed to the wrong commit in my V1/V2 posting. This may have caused some confusion. The actual commit to blame is 170b04b7ae49 ("mm/workingset: prepare the workingset detection infrastructure for anon LRU"). I will be posting my V3 soon. It has a much better commit log and fixes a issue that was present in my V2.

This new change allows for challenging the anon memory at a much greater rate. I believe this is ok since it will cause less trashing; however, it may also be the case that the user wants to avoid paying the cost of writing the anon to swap, and would rather throttle the page reads (like has been the case since at least rhel5).

Hopefully my V3 clears up a lot of the questions asked, and my motivations for these changes is more clear.

Cheers!

-- Nico