Re: mm/compact: why use low watermark to determine whether compact is finished instead of use high watermark?
From: Xishi Qiu
Date: Fri Jul 22 2016 - 05:33:55 EST
On 2016/7/22 17:04, Vlastimil Babka wrote:
> On 07/22/2016 10:56 AM, Xishi Qiu wrote:
>> I find all the watermarks in mm/compaction.c are low_wmark_pages(),
>> so why not use high watermark to determine whether compact is finished?
> Why would you use high watermark? Quite the opposite, I want to move towards min watermark (precisely, the one in alloc_flags which is usually min) in this series:
>> this is fast path, use use low_wmark_pages() in __zone_watermark_ok()
>> this is slow path, usually use min_wmark_pages()
> Yes, and compaction should be finished when allocation can succeed, so match __alloc_pages_slowpath().
Sounds reasonable, but now we have kcompactd which called from kswapd,
so still use low wmark?
>> use high_wmark_pages() to determine whether zone is balanced
>> Xishi Qiu