linux-kernel - Re: [PATCH 4/5] mm/compaction: check pageblock suitability once per pageblock

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Date:	Mon, 10 Feb 2014 09:46:26 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] mm/compaction: check pageblock suitability once per
 pageblock

On Fri, Feb 07, 2014 at 11:30:02AM +0100, Vlastimil Babka wrote:
> On 02/07/2014 06:08 AM, Joonsoo Kim wrote:
> > isolation_suitable() and migrate_async_suitable() is used to be sure
> > that this pageblock range is fine to be migragted. It isn't needed to
> > call it on every page. Current code do well if not suitable, but, don't
> > do well when suitable. It re-check it on every valid pageblock.
> > This patch fix this situation by updating last_pageblock_nr.
> 
> It took me a while to understand that the problem with migrate_async_suitable() was the
> lack of last_pageblock_nr updates (when the code doesn't go through next_pageblock:
> label), while the problem with isolation_suitable() was the lack of doing the test only
> when last_pageblock_nr != pageblock_nr (so two different things). How bout making it
> clearer in the changelog by replacing the paragraph above with something like:

Really nice!!
Sorry for bad description and thanks for taking time to understand it.

> 
> <snip>
> isolation_suitable() and migrate_async_suitable() is used to be sure
> that this pageblock range is fine to be migragted. It isn't needed to
> call it on every page. Current code do well if not suitable, but, don't
> do well when suitable.
> 
> 1) It re-checks isolation_suitable() on each page of a pageblock that was already
> estabilished as suitable.
> 2) It re-checks migrate_async_suitable() on each page of a pageblock that was not entered
> through the next_pageblock: label, because last_pageblock_nr is not otherwise updated.
> 
> This patch fixes situation by 1) calling isolation_suitable() only once per pageblock and
> 2) always updating last_pageblock_nr to the pageblock that was just checked.
> </snip>
> 
> > Additionally, move PageBuddy() check after pageblock unit check,
> > since pageblock check is the first thing we should do and makes things
> > more simple.
> 
> You should also do this, since it becomes redundant and might only confuse people:
> 
>  next_pageblock:
>                  low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
> -                last_pageblock_nr = pageblock_nr;
> 

Okay.

> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> With the above resolved, consider the patch to be
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

I will do it.
Thanks!
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