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

[Zhaoyang Huang]

On Sat, Oct 7, 2023 at 5:17 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> 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?
I have applied this patch in a v5.4 based ANDROID system and got no
regression problem. Actually, this commit is aimed to have
alloc_pages(GFP_USER) use CMA instead of stealing U&R(could lead to
GFP_KERNEL fail) only when zone's free pages and free cma are around
WATERMARK_LOW/MIN which would NOT affect most scenarios.
>
> Thanks.
>