Re: [PATCHv5] mm: optimization on page allocation when CMA enabled

[Andrew Morton]

On Thu, 11 May 2023 13:22:30 +0800 "zhaoyang.huang" <zhaoyang.huang@xxxxxxxxxx> wrote:

> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> 
> Let us look at the timeline of scenarios below with WMARK_LOW=25MB WMARK_MIN=5MB
> (managed pages 1.9GB). We can find that CMA begin to be used until 'C' under the
> method of 'fixed 2 times of free cma over free pages' which could have the
> scenario 'A' and 'B' into a fault state, that is, free UNMOVABLE & RECLAIMABLE
> pages is lower than corresponding watermark without reclaiming which should be
> deemed as against current memory policy. This commit try to solve this by
> checking zone_watermark_ok again with removing CMA pages which could lead to a
> proper time point of CMA's utilization.
> 
> -- Free_pages
> |
> |
> -- WMARK_LOW
> |
> -- Free_CMA
> |
> |
> --
> 
> Free_CMA/Free_pages(MB)      A(12/30) -->  B(12/25) -->  C(12/20)
> fixed 1/2 ratio                 N             N           Y
> this commit                     Y             Y           Y
> 

Roman previously asked

: Also I'm a bit concerned about potential performance implications. 
: Would be great to provide some benchmarks or some data.  Probably it's
: ok because of we have pcp caches on top, but I'm not 100% sure.

Are you able to perform such testing and tell us the result?

Thanks.