linux-kernel - Re: [RFC PATCH 12/26] mm: page_alloc: per-migratetype free counts

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Message-ID: <20230421153501.GE320347@cmpxchg.org>
Date:   Fri, 21 Apr 2023 11:35:01 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     linux-mm@...ck.org, Kaiyang Zhao <kaiyang2@...cmu.edu>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [RFC PATCH 12/26] mm: page_alloc: per-migratetype free counts

On Fri, Apr 21, 2023 at 03:28:41PM +0100, Mel Gorman wrote:
> On Tue, Apr 18, 2023 at 03:12:59PM -0400, Johannes Weiner wrote:
> > Increase visibility into the defragmentation behavior by tracking and
> > reporting per-migratetype free counters.
> > 
> > Subsequent patches will also use those counters to make more targeted
> > reclaim/compaction decisions.
> > 
> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> 
> Visibility into fragmentation behaviour is information that is
> almost certainly only useful to a developer and even then, there is
> /proc/pagetypeinfo. At minimum, move this patch to later in the series
> but I'm skeptical about its benefit.

Having them available in the memory dump (OOM, sysrq) was essential
while debugging problems in later patches. For OOMs or lockups,
pagetypeinfo isn't available. It would be useful to have them included
in user reports if any issues pop up.

They're used internally in several places later on, too.

I'll expand on the changelog and move them ahead in the series.

Thanks