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Date: Wed, 2 Mar 2016 23:59:08 +0900
Message-ID: <CAAmzW4METKGH27_tcnBLp1CQU3UK+YmfXJ4MwHuwUfqynAp_eg@mail.gmail.com>
Subject: Re: [PATCH v2 4/5] mm, kswapd: replace kswapd compaction with waking
 up kcompactd
From: Joonsoo Kim <js1304@gmail.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Rik van Riel <riel@redhat.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        David Rientjes <rientjes@google.com>, Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>
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2016-03-02 23:40 GMT+09:00 Vlastimil Babka <vbabka@suse.cz>:
> On 03/02/2016 03:22 PM, Joonsoo Kim wrote:
>> 2016-03-02 23:09 GMT+09:00 Vlastimil Babka <vbabka@suse.cz>:
>>> On 03/02/2016 02:57 PM, Joonsoo Kim wrote:
>>>>
>>>>
>>>> Yes, I know.
>>>> What I'd like to say here is that you need to care current_is_kswapd() in
>>>> this patch. This patch unintentionally change the back ground compaction
>>>> thread
>>>> behaviour to restart compaction by every 64 trials because calling
>>>> curret_is_kswapd()
>>>
>>>> by kcompactd would return false and is treated as direct reclaim.
>>>
>>> Oh, you mean this path to reset the skip bits. I see. But if skip bits are
>>> already reset by kswapd when waking kcompactd, then effect of another (rare)
>>> reset in kcompactd itself will be minimal?
>>
>> If you care current_is_kswapd() in this patch properly (properly means change
>> like "current_is_kcompactd()), reset in kswapd would not
>> happen because, compact_blockskip_flush would not be set by kcompactd.
>>
>> In this case, patch 5 would have it's own meaning so cannot be folded.
>
> So I understand that patch 5 would be just about this?
>
> -       if (compaction_restarting(zone, cc->order) && !current_is_kcompactd())
> +       if (compaction_restarting(zone, cc->order))
>                 __reset_isolation_suitable(zone);

Yeah, you understand correctly. :)

> I'm more inclined to fold it in that case.

Patch would be just simple, but, I guess it would cause some difference
in test result. But, I'm okay for folding.

Thanks.