linux-kernel - Re: [PATCH 3/3] oom, trace: add compaction retry tracepoint

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Date:   Wed, 14 Dec 2016 19:11:34 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] oom, trace: add compaction retry tracepoint

On Wed 14-12-16 18:28:38, Vlastimil Babka wrote:
> On 12/14/2016 03:53 PM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > Higher order requests oom debugging is currently quite hard. We do have
> > some compaction points which can tell us how the compaction is operating
> > but there is no trace point to tell us about compaction retry logic.
> > This patch adds a one which will have the following format
> > 
> >             bash-3126  [001] ....  1498.220001: compact_retry: order=9 priority=COMPACT_PRIO_SYNC_LIGHT compaction_result=withdrawn retries=0 max_retries=16 should_retry=0
> > 
> > we can see that the order 9 request is not retried even though we are in
> > the highest compaction priority mode becase the last compaction attempt
> > was withdrawn. This means that compaction_zonelist_suitable must have
> > returned false and there is no suitable zone to compact for this request
> > and so no need to retry further.
> > 
> > another example would be
> >            <...>-3137  [001] ....    81.501689: compact_retry: order=9 priority=COMPACT_PRIO_SYNC_LIGHT compaction_result=failed retries=0 max_retries=16 should_retry=0
> > 
> > in this case the order-9 compaction failed to find any suitable
> > block. We do not retry anymore because this is a costly request
> > and those do not go below COMPACT_PRIO_SYNC_LIGHT priority.
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> > ---
> >  include/trace/events/mmflags.h | 26 ++++++++++++++++++++++++++
> >  include/trace/events/oom.h     | 39 +++++++++++++++++++++++++++++++++++++++
> >  mm/page_alloc.c                | 22 ++++++++++++++++------
> >  3 files changed, 81 insertions(+), 6 deletions(-)
> > 
> > diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> > index 7e4cfede873c..aa4caa6914a9 100644
> > --- a/include/trace/events/mmflags.h
> > +++ b/include/trace/events/mmflags.h
> > @@ -187,8 +187,32 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY,	"softdirty"	)		\
> >  	EM( COMPACT_NO_SUITABLE_PAGE,	"no_suitable_page")	\
> >  	EM( COMPACT_NOT_SUITABLE_ZONE,	"not_suitable_zone")	\
> >  	EMe(COMPACT_CONTENDED,		"contended")
> > +
> > +/* High-level compaction status feedback */
> > +#define COMPACTION_FAILED	1
> > +#define COMPACTION_WITHDRAWN	2
> > +#define COMPACTION_PROGRESS	3
> > +
> > +#define compact_result_to_feedback(result)	\
> > +({						\
> > + 	enum compact_result __result = result;	\
> > +	(compaction_failed(__result)) ? COMPACTION_FAILED : \
> > +		(compaction_withdrawn(__result)) ? COMPACTION_WITHDRAWN : COMPACTION_PROGRESS; \
> > +})
> 
> It seems you forgot to actually use this "function" (sorry, didn't notice
> earlier) so currently it's translating enum compact_result directly into the
> failed/withdrawn/progress strings, which is wrong.

You are right. I've screwed while integrating the enum translation part.

> The correct place for the result->feedback conversion should be
> TP_fast_assign, so __entry->result should become __entry->feedback. It's too
> late in TP_printk, as userspace tools (e.g. trace-cmd) won't know the
> functions that compact_result_to_feedback() uses.

Thanks. The follow up fix should be
---
>From 82c9064698594d694b052d3847c905e90becc7c5 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.com>
Date: Wed, 14 Dec 2016 19:09:10 +0100
Subject: [PATCH] fold me "oom, trace: add compaction retry tracepoint"

Do not forget to translate compact_result into a highlevel constants
as per Vlastimil

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 include/trace/events/oom.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/trace/events/oom.h b/include/trace/events/oom.h
index e9d690665b7a..38baeb27221a 100644
--- a/include/trace/events/oom.h
+++ b/include/trace/events/oom.h
@@ -94,7 +94,7 @@ TRACE_EVENT(compact_retry,
 	TP_fast_assign(
 		__entry->order = order;
 		__entry->priority = priority;
-		__entry->result = result;
+		__entry->result = compact_result_to_feedback(result);
 		__entry->retries = retries;
 		__entry->max_retries = max_retries;
 		__entry->ret = ret;
-- 
2.10.2

-- 
Michal Hocko
SUSE Labs