linux-kernel - Re: [PATCH v6 02/19] mm: memcg: prepare for byte-sized vmstat items

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Date:   Wed, 17 Jun 2020 08:55:22 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Kernel Team <kernel-team@...com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 02/19] mm: memcg: prepare for byte-sized vmstat items

On Mon, Jun 8, 2020 at 4:07 PM Roman Gushchin <guro@...com> wrote:
>
> To implement per-object slab memory accounting, we need to
> convert slab vmstat counters to bytes. Actually, out of
> 4 levels of counters: global, per-node, per-memcg and per-lruvec
> only two last levels will require byte-sized counters.
> It's because global and per-node counters will be counting the
> number of slab pages, and per-memcg and per-lruvec will be
> counting the amount of memory taken by charged slab objects.
>
> Converting all vmstat counters to bytes or even all slab
> counters to bytes would introduce an additional overhead.
> So instead let's store global and per-node counters
> in pages, and memcg and lruvec counters in bytes.
>
> To make the API clean all access helpers (both on the read
> and write sides) are dealing with bytes.
>
> To avoid back-and-forth conversions a new flavor of read-side
> helpers is introduced, which always returns values in pages:
> node_page_state_pages() and global_node_page_state_pages().
>
> Actually new helpers are just reading raw values. Old helpers are
> simple wrappers, which will complain on an attempt to read
> byte value, because at the moment no one actually needs bytes.
>
> Thanks to Johannes Weiner for the idea of having the byte-sized API
> on top of the page-sized internal storage.
>
> Signed-off-by: Roman Gushchin <guro@...com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>