On 07/22/2016 11:21 AM, Xishi Qiu wrote:
On 2016/7/22 17:04, Vlastimil Babka wrote:
On 07/22/2016 10:56 AM, Xishi Qiu wrote:
Hi,
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:
https://lkml.org/lkml/2016/6/24/222
especially:
https://lkml.org/lkml/2016/6/24/214
e.g.
__alloc_pages_nodemask()
get_page_from_freelist()
this is fast path, use use low_wmark_pages() in __zone_watermark_ok()
__alloc_pages_slowpath()
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?
kswapd uses high watermark (order-0) to make a buffer of free pages for
both direct allocators and kcompactd. kcompactd will use min watermark
for now. There used to be difference between min/low/high watermarks
when checking high-orders, but now watermark only affects the check if
there's enough total base pages, and high-order check then succeeds if
there's at least one high(er)-order page.
Thanks,
Xishi Qiu
kswapd
balance_pgdat()
use high_wmark_pages() to determine whether zone is balanced
Thanks,
Xishi Qiu
.
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