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On 02/12/2015 03:18 AM, Vlastimil Babka wrote:
> On 02/11/2015 10:09 PM, Andrew Morton wrote:
>>> 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?
>>
>
> Commit 35cd78156c "vmscan: throttle direct reclaim when too many
> pages are isolated already" by Rik seems to have introduced this
> congestion_wait() based on too_many_isolated(). The bug it was
> fixing:
>
> "When way too many processes go into direct reclaim, it is possible
> for all of the pages to be taken off the LRU. One result of this is
> that the next process in the page reclaim code thinks there are no
> reclaimable pages left and triggers an out of memory kill."
>
> So either this is now prevented by something else and
> too_many_isolated() could go away, or we should restore its
> functionality. Any idea, Rik?
I don't think that bug is prevented.
I have seen reports of OOM kills happening while the system
still has a lot of reclaimable page cache pages.
This might actually help explain that bug...
- --
All rights reversed
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