linux-kernel - Re: [PATCH 0/1] Add swappiness argument to memory.reclaim

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Date:   Thu, 30 Nov 2023 18:44:24 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Dan Schatzberg <schatzberg.dan@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Yosry Ahmed <yosryahmed@...gle.com>, Huan Yang <link@...o.com>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Huang Ying <ying.huang@...el.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Peter Xu <peterx@...hat.com>,
        "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        Yue Zhao <findns94@...il.com>, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 0/1] Add swappiness argument to memory.reclaim

On Thu, Nov 30, 2023 at 07:36:53AM -0800, Dan Schatzberg wrote:
> (Sorry for the resend - forgot to cc the mailing lists)
> 
> This patch proposes augmenting the memory.reclaim interface with a
> swappiness=<val> argument that overrides the swappiness value for that instance
> of proactive reclaim.
> 
> Userspace proactive reclaimers use the memory.reclaim interface to trigger
> reclaim. The memory.reclaim interface does not allow for any way to effect the
> balance of file vs anon during proactive reclaim. The only approach is to adjust
> the vm.swappiness setting. However, there are a few reasons we look to control
> the balance of file vs anon during proactive reclaim, separately from reactive
> reclaim:
> 
> * Swapout should be limited to manage SSD write endurance. In near-OOM

Is this about swapout to SSD only?

>   situations we are fine with lots of swap-out to avoid OOMs. As these are
>   typically rare events, they have relatively little impact on write endurance.
>   However, proactive reclaim runs continuously and so its impact on SSD write
>   endurance is more significant. Therefore it is desireable to control swap-out
>   for proactive reclaim separately from reactive reclaim

This is understandable but swapout to zswap should be fine, right?
(Sorry I am not following the discussion on zswap patches from Nhat. Is
the answer there?)