linux-kernel - Re: [PATCH v3 03/19] mm: memcg: convert vmstat slab counters to bytes

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Message-ID: <20200507204137.GC161043@cmpxchg.org>
Date:   Thu, 7 May 2020 16:41:37 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        kernel-team@...com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 03/19] mm: memcg: convert vmstat slab counters to bytes

On Wed, Apr 22, 2020 at 01:46:52PM -0700, Roman Gushchin wrote:
> In order to prepare for per-object slab memory accounting, convert
> NR_SLAB_RECLAIMABLE and NR_SLAB_UNRECLAIMABLE vmstat items to bytes.
> 
> To make it obvious, rename them to NR_SLAB_RECLAIMABLE_B and
> NR_SLAB_UNRECLAIMABLE_B (similar to NR_KERNEL_STACK_KB).
> 
> Internally global and per-node counters are stored in pages,
> however memcg and lruvec counters are stored in bytes.
> This scheme may look weird, but only for now. As soon as slab
> pages will be shared between multiple cgroups, global and
> node counters will reflect the total number of slab pages.
> However memcg and lruvec counters will be used for per-memcg
> slab memory tracking, which will take separate kernel objects
> in the account. Keeping global and node counters in pages helps
> to avoid additional overhead.
> 
> The size of slab memory shouldn't exceed 4Gb on 32-bit machines,
> so it will fit into atomic_long_t we use for vmstats.
> 
> Signed-off-by: Roman Gushchin <guro@...com>

Acked-by: Johannes Weiner <hannes@...xchg.org>

Thanks for splitting this out, it makes both this and the previous
patch easier to read.