linux-kernel - Re: [PATCH v6 6/9] mm: multigenerational lru: aging

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Date:   Fri, 7 Jan 2022 10:00:31 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        page-reclaim@...gle.com, x86@...nel.org,
        Konstantin Kharlamov <Hi-Angel@...dex.ru>
Subject: Re: [PATCH v6 6/9] mm: multigenerational lru: aging

On Fri 07-01-22 09:55:09, Michal Hocko wrote:
[...]
> > In this case, lru_gen_mm_walk is small (160 bytes); it's per direct
> > reclaimer; and direct reclaimers rarely come here, i.e., only when
> > kswapd can't keep up in terms of the aging, which is similar to the
> > condition where the inactive list is empty for the active/inactive
> > lru.
> 
> Well, this is not a strong argument to be honest. Kswapd being stuck
> and the majority of the reclaim being done in the direct reclaim
> context is a situation I have seen many many times.

Also do not forget that memcg reclaim is effectivelly only direct
reclaim. Not that the memcg reclaim indicates a global memory shortage
but it can add up and race with the global reclaim as well.

-- 
Michal Hocko
SUSE Labs