Re: [PATCH] vmscan: fix zone balance check in prepare_kswapd_sleep

[Vlastimil Babka <vbabka@suse.cz>]

On 02/07/2017 01:16 AM, Shantanu Goel wrote:
> Hi,
>
> On 02/06/2017 11:17 AM, Mel Gorman wrote:
>
>> On Sun, Feb 05, 2017 at 12:46:20PM +0000, Shantanu Goel wrote:
>>> On 4.9.7 kswapd is failing to wake up kcompactd due to a mismatch in the zone balance check between balance_pgdat() and prepare_kswapd_sleep().  balance_pgdat() returns as soon as a single zone satisfies the allocation but prepare_kswapd_sleep() requires all zones to do the same.  This causes prepare_kswapd_sleep() to never succeed except in the order == 0 case and consequently, wakeup_kcompactd() is never called.  On my machine prior to apply this patch, the state of compaction from /proc/vmstat looked this way after a day and a half of uptime:
>>>
>>> compact_migrate_scanned 240496
>>> compact_free_scanned 76238632
>>> compact_isolated 123472
>>> compact_stall 1791
>>> compact_fail 29
>>> compact_success 1762
>>> compact_daemon_wake 0
>>>
>>>
>>> After applying the patch and about 10 hours of uptime the state looks like this:
>>>
>>> compact_migrate_scanned 59927299
>>> compact_free_scanned 2021075136
>>> compact_isolated 640926
>>> compact_stall 4
>>> compact_fail 2
>>> compact_success 2
>>> compact_daemon_wake 5160

I've just seen similar results in a test, so you can add:

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

Thanks!

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