linux-kernel - Re: [PATCH v5 1/5] mm,page_alloc: Bail out earlier on -ENOMEM in alloc_contig_migrate

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Message-ID: <YFM7iFnwlLFUSiAz@dhcp22.suse.cz>
Date:   Thu, 18 Mar 2021 12:37:44 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/5] mm,page_alloc: Bail out earlier on -ENOMEM in
 alloc_contig_migrate_range

On Thu 18-03-21 12:04:00, Oscar Salvador wrote:
> On Wed, Mar 17, 2021 at 03:05:40PM +0100, Michal Hocko wrote:
> > That being said, bailing out early makes sense to me. But now that
> > you've made me look into the migrate_pages excellent error state reporting
> > I suspect we have a bug here. Note the 
> > "Returns the number of pages that were not migrated, or an error code."
> > 
> > but I do not see putback_movable_pages for ret > 0 so it seems we might
> > leak some pages.
> 
> I fell for the same thing when looking at that code.
> It took a while until I realized what was really going on.
> 
> > > Signed-off-by: Oscar Salvador <osalvador@...e.de>
> > > Acked-by: Vlastimil Babka <vbabka@...e.cz>
> > > Reviewed-by: David Hildenbrand <david@...hat.com>
> > 
> > The patch itself looks reasonable but make sure to mention this is mere
> > cosmetic change unless there is a real problem fixed by this.
> > Acked-by: Michal Hocko <mhocko@...e.com>
> 
> What about appending the following in the changelog:
> 
> "Note that this is not fixing a real issue, just a cosmetic change. Although
>  we can save some cycles by backing off ealier."

Sounds good to me.

-- 
Michal Hocko
SUSE Labs