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Subject: Re: [PATCH] mm/vmscan: DRY cleanup for do_try_to_free_pages()
To:     Michal Hocko <mhocko@suse.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org
References: <20201218102217.186836-1-jian.w.wen@oracle.com>
 <20201218105153.GX32193@dhcp22.suse.cz>
From:   Jacob Wen <jian.w.wen@oracle.com>
Message-ID: <f376b551-9a90-c036-d34b-b32d93107b6c@oracle.com>
Date:   Fri, 18 Dec 2020 21:51:48 +0800
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On 12/18/20 6:51 PM, Michal Hocko wrote:
> On Fri 18-12-20 18:22:17, Jacob Wen wrote:
>> This patch reduces repetition of set_task_reclaim_state() around
>> do_try_to_free_pages().
> The changelog really should be talking about why this is needed/useful.
>  From the above it is not really clear whether you aimed at doing
> a clean up or this is a fix for some misbehavior. I do assume the former
> but this should be clearly articulated.

How about this?

mm/vmscan: remove duplicate code around do_try_to_free_pages()

This patch moves set_task_reclaim_state() into do_try_to_free_pages()
to avoid unnecessary repetition. It doesn't introduce functional
change.

>
>> Signed-off-by: Jacob Wen <jian.w.wen@oracle.com>
>> ---
>>   mm/vmscan.c | 27 ++++++++++++++++-----------
>>   1 file changed, 16 insertions(+), 11 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 257cba79a96d..4bc244b23686 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -3023,6 +3023,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>>   	pg_data_t *last_pgdat;
>>   	struct zoneref *z;
>>   	struct zone *zone;
>> +	unsigned long ret;
>> +
>> +	set_task_reclaim_state(current, &sc->reclaim_state);
>> +
>>   retry:
>>   	delayacct_freepages_start();
>>   
>> @@ -3069,12 +3073,16 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>>   
>>   	delayacct_freepages_end();
>>   
>> -	if (sc->nr_reclaimed)
>> -		return sc->nr_reclaimed;
>> +	if (sc->nr_reclaimed) {
>> +		ret = sc->nr_reclaimed;
>> +		goto out;
>> +	}
>>   
>>   	/* Aborted reclaim to try compaction? don't OOM, then */
>> -	if (sc->compaction_ready)
>> -		return 1;
>> +	if (sc->compaction_ready) {
>> +		ret = 1;
>> +		goto out;
>> +	}
>>   
>>   	/*
>>   	 * We make inactive:active ratio decisions based on the node's
>> @@ -3101,7 +3109,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>>   		goto retry;
>>   	}
>>   
>> -	return 0;
>> +	ret = 0;
>> +out:
>> +	set_task_reclaim_state(current, NULL);
>> +	return ret;
>>   }
>>   
>>   static bool allow_direct_reclaim(pg_data_t *pgdat)
>> @@ -3269,13 +3280,11 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
>>   	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
>>   		return 1;
>>   
>> -	set_task_reclaim_state(current, &sc.reclaim_state);
>>   	trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
>>   
>>   	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
>>   
>>   	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
>> -	set_task_reclaim_state(current, NULL);
>>   
>>   	return nr_reclaimed;
>>   }
>> @@ -3347,7 +3356,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>>   	 */
>>   	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
>>   
>> -	set_task_reclaim_state(current, &sc.reclaim_state);
>>   	trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
>>   	noreclaim_flag = memalloc_noreclaim_save();
>>   
>> @@ -3355,7 +3363,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>>   
>>   	memalloc_noreclaim_restore(noreclaim_flag);
>>   	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
>> -	set_task_reclaim_state(current, NULL);
>>   
>>   	return nr_reclaimed;
>>   }
>> @@ -4023,11 +4030,9 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
>>   
>>   	fs_reclaim_acquire(sc.gfp_mask);
>>   	noreclaim_flag = memalloc_noreclaim_save();
>> -	set_task_reclaim_state(current, &sc.reclaim_state);
>>   
>>   	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
>>   
>> -	set_task_reclaim_state(current, NULL);
>>   	memalloc_noreclaim_restore(noreclaim_flag);
>>   	fs_reclaim_release(sc.gfp_mask);
>>   
>> -- 
>> 2.25.1
>>