linux-kernel - Re: [PATCH 1/2] mm/compaction: fix invalid free_pfn and compact_cached_free

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Date:	Wed, 16 Dec 2015 14:44:45 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Aaron Lu <aaron.lu@...el.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH 1/2] mm/compaction: fix invalid free_pfn and
 compact_cached_free_pfn

On Tue, Dec 15, 2015 at 09:31:39AM +0100, Vlastimil Babka wrote:
> On 12/14/2015 04:26 PM, Joonsoo Kim wrote:
> >2015-12-14 19:07 GMT+09:00 Vlastimil Babka <vbabka@...e.cz>:
> >>On 12/14/2015 06:02 AM, Joonsoo Kim wrote:
> >>>
> >>
> >>Acked-by: Vlastimil Babka <vbabka@...e.cz>
> >>
> >>Note that until now in compaction we've used basically an open-coded
> >>round_down(), and ALIGN() for rounding up. You introduce a first use of
> >>round_down(), and it would be nice to standardize on round_down() and
> >>round_up() everywhere. I think it's more obvious than open-coding and
> >>ALIGN() (which doesn't tell the reader if it's aligning up or down).
> >>Hopefully they really do the same thing and there are no caveats...
> >
> >Okay. Will send another patch for this clean-up on next spin.
> 
> Great, I didn't mean that the cleanup is needed right now, but
> whether we agree on an idiom to use whenever doing any changes from
> now on.

Okay.

> Maybe it would be best to add some defines in the top of
> compaction.c that would also hide away the repeated
> pageblock_nr_pages everywhere? Something like:
> 
> #define pageblock_start(pfn) round_down(pfn, pageblock_nr_pages)
> #define pageblock_end(pfn) round_up((pfn)+1, pageblock_nr_pages)

Quick grep shows that there are much more places this new define or
some variant can be used. It would be good clean-up. I will try it
separately.

Thanks.
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