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Message-Id: <20240612090040.090c20a398f3e9eb550e1a9d@linux-foundation.org>
Date: Wed, 12 Jun 2024 09:00:40 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Hugh Dickins <hughd@...gle.com>
Cc: "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>, Baolin
Wang <baolin.wang@...ux.alibaba.com>, David Hildenbrand <david@...hat.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH hotfix] mm/migrate: fix kernel BUG at
mm/compaction.c:2761!
On Wed, 12 Jun 2024 00:11:44 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:
> > It appears better to add
> >
> > stats->nr_thp_failed++;
> >
> > too. Otherwise, if migrate_pages_batch() is called via migrate_pages(,
> > MIGRATE_ASYNC, ), nr_thp_failed will not increase. But if
> > migrate_pages_batch() is called via migrate_pages(, MIGRATE_SYNC*, ),
> > nr_thp_failed will increase in migrate_pages_sync() via
> >
> > stats->nr_thp_failed += astats.nr_thp_split;
> >
> > That is, they are not consistent. The issue exists since commit
> > 7262f208ca68 ("mm/migrate: split source folio if it is on deferred split
> > list").
>
> Sorry, I'll have to let you take over and send your own patch instead
> of mine - thanks. Those stats, and any attempt at consistency there,
> is way beyond me! I thought consistency was impossible, unless all
> the numbers were changed to order-0 counts.
I'll add this patch as-is for now.
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