On Tue, 10 Feb 2015 23:06:09 -0800 (PST) Hugh Dickins <hughd@xxxxxxxxxx> 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.
So if I'm understanding this correctly, shrink_inactive_list()'s call
to congestion_wait() basically never happens?
If so I'm pretty reluctant to merge this up until it has had plenty of
careful testing - there's a decent chance that it will make the kernel
behave worse.
> Fixes: edc2ca612496 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v3.18+
And why -stable? What user-visible problem is the bug causing?
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