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

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Message-Id: <20231006141750.5423083520f74bc0746fd249@linux-foundation.org>
Date:   Fri, 6 Oct 2023 14:17:50 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc:     Roman Gushchin <guro@...com>, Minchan Kim <minchan@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        Zhaoyang Huang <huangzhaoyang@...il.com>, <ke.wang@...soc.com>
Subject: Re: [PATCHv5] mm: optimization on page allocation when CMA enabled

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

> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> 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.