linux-kernel - Re: [PATCH 09/19] mm: memcontrol: switch to native NR_FILE_PAGES and NR

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Message-ID: <20200610164222.GE20204@dhcp22.suse.cz>
Date:   Wed, 10 Jun 2020 18:42:22 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Joonsoo Kim <js1304@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 09/19] mm: memcontrol: switch to native NR_FILE_PAGES and
 NR_SHMEM counters

On Fri 08-05-20 14:30:56, Johannes Weiner wrote:
> Memcg maintains private MEMCG_CACHE and NR_SHMEM counters. This
> divergence from the generic VM accounting means unnecessary code
> overhead, and creates a dependency for memcg that page->mapping is set
> up at the time of charging, so that page types can be told apart.
> 
> Convert the generic accounting sites to mod_lruvec_page_state and
> friends to maintain the per-cgroup vmstat counters of NR_FILE_PAGES
> and NR_SHMEM. The page is already locked in these places, so
> page->mem_cgroup is stable; we only need minimal tweaks of two
> mem_cgroup_migrate() calls to ensure it's set up in time.
> 
> Then replace MEMCG_CACHE with NR_FILE_PAGES and delete the private
> NR_SHMEM accounting sites.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@....com>

While looking at the code I've noticed that add_to_swap_cache resp.
__delete_from_swap_cache are accounting only to global counters.
Is there any reason for that? Not something that this patch is
responsible for of course but I am just wondering.
-- 
Michal Hocko
SUSE Labs