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

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Message-ID: <54ABC6AF.1020108@suse.cz>
Date:	Tue, 06 Jan 2015 12:27:43 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	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 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.

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