Re: [PATCH] mm: fix negative nr_isolated counts

[Vlastimil Babka <vbabka@suse.cz>]

On 02/11/2015 08:06 AM, Hugh Dickins wrote:
> The vmstat interfaces are good at hiding negative counts (at least
> when CONFIG_SMP); but if you peer behind the curtain, you find that
> nr_isolated_anon and nr_isolated_file soon go negative, and grow ever
> more negative: so they can absorb larger and larger numbers of isolated
> pages, yet still appear to be zero.
>
> I'm happy to avoid a congestion_wait() when too_many_isolated() myself;
> but I guess it's there for a good reason, in which case we ought to get
> too_many_isolated() working again.
>
> The imbalance comes from isolate_migratepages()'s ISOLATE_ABORT case:
> putback_movable_pages() decrements the NR_ISOLATED counts, but we forgot
> to call acct_isolated() to increment them.
>
> Fixes: edc2ca612496 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")

Ccing Joonsoo for completeness, as it seems he contributed to this part 
[1] (to fix another bug of mine, not trying to dismiss responsibility)

But yeah it looks correct. Thanks for finding and fixing!

Acked-by: Vlastimil Babka <vbabka@suse.cz>

[1] https://lkml.org/lkml/2014/9/29/60

> Signed-off-by: Hugh Dickins <hughd@google.com>
> Cc: stable@vger.kernel.org # v3.18+
> ---
>
>   mm/compaction.c |    4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> --- v3.19/mm/compaction.c	2015-02-08 18:54:22.000000000 -0800
> +++ linux/mm/compaction.c	2015-02-10 22:25:04.613907871 -0800
> @@ -1015,8 +1015,10 @@ static isolate_migrate_t isolate_migrate
>   		low_pfn = isolate_migratepages_block(cc, low_pfn, end_pfn,
>   								isolate_mode);
>
> -		if (!low_pfn || cc->contended)
> +		if (!low_pfn || cc->contended) {
> +			acct_isolated(zone, cc);
>   			return ISOLATE_ABORT;
> +		}
>
>   		/*
>   		 * Either we isolated something and proceed with migration. Or
>

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