linux-kernel - Re: [PATCH 3/3] mm/compaction: add tracepoint to observe behaviour of compaction defer

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Message-ID: <20150108082353.GE25453@js1304-P5Q-DELUXE>
Date:	Thu, 8 Jan 2015 17:23:53 +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>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm/compaction: add tracepoint to observe behaviour
 of compaction defer

On Tue, Jan 06, 2015 at 12:27:43PM +0100, Vlastimil Babka wrote:
> On 12/03/2014 08:52 AM, Joonsoo Kim wrote:
> > compaction deferring logic is heavy hammer that block the way to
> > the compaction. It doesn't consider overall system state, so it
> > could prevent user from doing compaction falsely. In other words,
> > even if system has enough range of memory to compact, compaction would be
> > skipped due to compaction deferring logic. This patch add new tracepoint
> > to understand work of deferring logic. This will also help to check
> > compaction success and fail.
> > 
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> You only call the tracepoints from try_to_compact_pages(), but the corresponding
> functions are also called from elsewhere, e.g. kswapd. Shouldn't all be
> included? Otherwise one might consider the trace as showing a bug, where the
> defer state suddenly changed without being captured in the trace.

Yes, I should include all the others. I also have experience of this
confusion.

Thanks.
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