linux-kernel - Re: [PATCH v5 2/5] mm,compaction: Let isolate_migratepages

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Date:   Thu, 18 Mar 2021 12:36:52 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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 2/5] mm,compaction: Let
 isolate_migratepages_{range,block} return error codes

On Thu 18-03-21 12:10:14, Vlastimil Babka wrote:
> On 3/18/21 11:22 AM, Michal Hocko wrote:
[...]
> > E.g. something like the following
> > diff --git a/mm/internal.h b/mm/internal.h
> > index 1432feec62df..6c5a9066adf0 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -225,7 +225,13 @@ struct compact_control {
> >  	unsigned int nr_freepages;	/* Number of isolated free pages */
> >  	unsigned int nr_migratepages;	/* Number of pages to migrate */
> >  	unsigned long free_pfn;		/* isolate_freepages search base */
> > -	unsigned long migrate_pfn;	/* isolate_migratepages search base */
> > +	unsigned long migrate_pfn;	/* Acts as an in/out parameter to page
> > +					 * isolation.
> > +					 * isolate_migratepages uses it as a search base.
> > +					 * isolate_migratepages_block will update the
> > +					 * value the next pfn after the last isolated
> > +					 * one.
> > +					 */
> 
> Fair enough. I would even stop pretending we might cram something useful in the
> rest of the line, and move all the comments to blocks before the variables.
> There might be more of them that would deserve more thorough description.

Yeah, makes sense. I am not a fan of the above form of documentation.
Btw. maybe renaming the field would be even better, both from the
intention and review all existing users. I would go with pfn_iter or
something that wouldn't make it sound like migration specific.

-- 
Michal Hocko
SUSE Labs