linux-kernel - Re: [PATCH 2/2] mm,thp,compaction,cma: allow THP migration for CMA allocations

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Message-ID: <67d927c6161b15664b4a912ad34fc3a147109760.camel@surriel.com>
Date:   Fri, 21 Feb 2020 17:35:15 -0500
From:   Rik van Riel <riel@...riel.com>
To:     Zi Yan <ziy@...dia.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        akpm@...ux-foundation.org, linux-mm@...ck.org, mhocko@...nel.org,
        vbabka@...e.cz, mgorman@...hsingularity.net, rientjes@...gle.com,
        aarcange@...hat.com
Subject: Re: [PATCH 2/2] mm,thp,compaction,cma: allow THP migration for CMA
 allocations

On Fri, 2020-02-21 at 17:31 -0500, Zi Yan wrote:
> On 21 Feb 2020, at 16:53, Rik van Riel wrote:
> 
> > +++ b/mm/compaction.c
> > @@ -894,12 +894,12 @@ isolate_migratepages_block(struct
> > compact_control *cc, unsigned long low_pfn,
> > 
> >  		/*
> >  		 * Regardless of being on LRU, compound pages such as
> > THP and
> > -		 * hugetlbfs are not to be compacted. We can
> > potentially save
> > -		 * a lot of iterations if we skip them at once. The
> > check is
> > -		 * racy, but we can consider only valid values and the
> > only
> > -		 * danger is skipping too much.
> > +		 * hugetlbfs are not to be compacted most of the time.
> > We can
> > +		 * potentially save a lot of iterations if we skip them
> > at
> > +		 * once. The check is racy, but we can consider only
> > valid
> > +		 * values and the only danger is skipping too much.
> >  		 */
> 
> Maybe add “we do want to move them when allocating contiguous memory
> using CMA” to help
> people understand the context of using cc->alloc_contig?

I can certainly do that.

I'll wait for feedback from other people to see if
more changes are wanted, and plan to post v2 by
Tuesday or so :)

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