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

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Date:   Wed, 4 Jan 2017 11:56:29 +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 04-01-17 11:47:56, Vlastimil Babka wrote:
> On 12/20/2016 02:01 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          bash-3126  [001] ....  1498.220001: compact_retry: order=9 priority=COMPACT_PRIO_SYNC_LIGHT compaction_result=withdrawn retries=0 max_retries=16 should_retry=0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 was withdrawn.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.
> > 
> > Changes since v1
> > - fix compaction_result into highlevel constants translation as per
> >   Vlastimil
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> > Acked-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Hmm I've noticed that I didn't suggest the following below here,
> although I did for the vmscan tracepoints now. How about adding this
> -fix for consistency?
> 
> --------8<--------
> From: Vlastimil Babka <vbabka@...e.cz>
> Date: Wed, 4 Jan 2017 11:44:09 +0100
> Subject: [PATCH] oom, trace: add compaction retry tracepoint-fix
> 
> Let's print the compaction priorities lower-case and without
> prefix for consistency.
> 
> Also indent fix in compact_result_to_feedback().
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

I would just worry that c&p constant name is easier to work with when
vim -t $PRIO or git grep $PRIO. But if the lowercase and shorter sounds
better to you then no objections from me.

> ---
>  include/trace/events/mmflags.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index aa4caa6914a9..e4c3a0febcce 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -195,7 +195,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY,	"softdirty"	)		\
>  
>  #define compact_result_to_feedback(result)	\
>  ({						\
> - 	enum compact_result __result = result;	\
> +	enum compact_result __result = result;	\
>  	(compaction_failed(__result)) ? COMPACTION_FAILED : \
>  		(compaction_withdrawn(__result)) ? COMPACTION_WITHDRAWN : COMPACTION_PROGRESS; \
>  })
> @@ -206,9 +206,9 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY,	"softdirty"	)		\
>  	EMe(COMPACTION_PROGRESS,	"progress")
>  
>  #define COMPACTION_PRIORITY						\
> -	EM(COMPACT_PRIO_SYNC_FULL,	"COMPACT_PRIO_SYNC_FULL")	\
> -	EM(COMPACT_PRIO_SYNC_LIGHT,	"COMPACT_PRIO_SYNC_LIGHT")	\
> -	EMe(COMPACT_PRIO_ASYNC,		"COMPACT_PRIO_ASYNC")
> +	EM(COMPACT_PRIO_SYNC_FULL,	"sync_full")	\
> +	EM(COMPACT_PRIO_SYNC_LIGHT,	"sync_light")	\
> +	EMe(COMPACT_PRIO_ASYNC,		"async")
>  #else
>  #define COMPACTION_STATUS
>  #define COMPACTION_PRIORITY
> -- 
> 2.11.0
> 

-- 
Michal Hocko
SUSE Labs