linux-kernel - Re: [PATCH v2 5/7] mm: rename and change semantics of nr_indirectly_reclaimable

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Date:   Mon, 2 Jul 2018 09:52:27 -0700
From:   Roman Gushchin <guro@...com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        <linux-api@...r.kernel.org>, Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Matthew Wilcox <willy@...radead.org>,
        Vijayanand Jitta <vjitta@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [PATCH v2 5/7] mm: rename and change semantics of
 nr_indirectly_reclaimable_bytes

On Sat, Jun 30, 2018 at 12:09:27PM +0200, Vlastimil Babka wrote:
> On 06/29/2018 11:12 PM, Roman Gushchin wrote:
> >>
> >> The vmstat counter NR_INDIRECTLY_RECLAIMABLE_BYTES was introduced by commit
> >> eb59254608bc ("mm: introduce NR_INDIRECTLY_RECLAIMABLE_BYTES") with the goal of
> >> accounting objects that can be reclaimed, but cannot be allocated via a
> >> SLAB_RECLAIM_ACCOUNT cache. This is now possible via kmalloc() with
> >> __GFP_RECLAIMABLE flag, and the dcache external names user is converted.
> >>
> >> The counter is however still useful for accounting direct page allocations
> >> (i.e. not slab) with a shrinker, such as the ION page pool. So keep it, and:
> > 
> > Btw, it looks like I've another example of usefulness of this counter:
> > dynamic per-cpu data.
> 
> Hmm, but are those reclaimable? Most likely not in general? Do you have
> examples that are?

If these per-cpu data is something like per-cpu refcounters,
which are using to manage reclaimable objects (e.g. cgroup css objects).
Of course, they are not always reclaimable, but in certain states.

Thanks!