linux-kernel - Re: [PATCH 1/3] mm: introduce NR_INDIRECTLY_RECLAIMABLE

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Date:   Thu, 12 Apr 2018 13:52:17 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm: introduce NR_INDIRECTLY_RECLAIMABLE_BYTES

On Thu 12-04-18 08:52:52, Vlastimil Babka wrote:
> On 04/11/2018 03:56 PM, Roman Gushchin wrote:
> > On Wed, Apr 11, 2018 at 03:16:08PM +0200, Vlastimil Babka wrote:
[...]
> >> With that in mind, can we at least for now put the (manually maintained)
> >> byte counter in a variable that's not directly exposed via /proc/vmstat,
> >> and then when printing nr_slab_reclaimable, simply add the value
> >> (divided by PAGE_SIZE), and when printing nr_slab_unreclaimable,
> >> subtract the same value. This way we would be simply making the existing
> >> counters more precise, in line with their semantics.
> > 
> > Idk, I don't like the idea of adding a counter outside of the vm counters
> > infrastructure, and I definitely wouldn't touch the exposed
> > nr_slab_reclaimable and nr_slab_unreclaimable fields.

Why?

> We would be just making the reported values more precise wrt reality.

I was suggesting something similar in an earlier discussion. I am not
really happy about the new exposed counter either. It is just arbitrary
by name yet very specific for this particular usecase.

What is a poor user supposed to do with the new counter? Can this be
used for any calculations?
-- 
Michal Hocko
SUSE Lab