Re: lot of MemAvailable but falling cache and raising PSI

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

Am 22.10.19 um 09:48 schrieb Vlastimil Babka:
> On 10/22/19 9:41 AM, Stefan Priebe - Profihost AG wrote:
>>> Hi, could you try the patch below? I suspect you're hitting a corner
>>> case where compaction_suitable() returns COMPACT_SKIPPED for the
>>> ZONE_DMA, triggering reclaim even if other zones have plenty of free
>>> memory. And should_continue_reclaim() then returns true until twice the
>>> requested page size is reclaimed (compact_gap()). That means 4MB
>>> reclaimed for each THP allocation attempt, which roughly matches the
>>> trace data you preovided previously.
>>>
>>> The amplification to 4MB should be removed in patches merged for 5.4, so
>>> it would be only 32 pages reclaimed per THP allocation. The patch below
>>> tries to remove this corner case completely, and it should be more
>>> visible on your 5.2.x, so please apply it there.
>>>
>> is there any reason to not apply that one on top of 4.19?
>>
>> Greets,
>> Stefan
>>
> 
> It should work, cherrypicks fine without conflict here.

OK but does not work ;-)


mm/compaction.c: In function '__compaction_suitable':
mm/compaction.c:1451:19: error: implicit declaration of function
'zone_managed_pages'; did you mean 'node_spanned_pages'?
[-Werror=implicit-function-declaration]
      alloc_flags, zone_managed_pages(zone)))
                   ^~~~~~~~~~~~~~~~~~
                   node_spanned_pages

Greets,
Stefan