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[47.88.44.36]) by mx.google.com with ESMTPS id l97si2404399pje.18.2019.05.23.22.38.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 May 2019 22:38:12 -0700 (PDT) Received-SPF: pass (google.com: domain of yang.shi@linux.alibaba.com designates 47.88.44.36 as permitted sender) client-ip=47.88.44.36; Authentication-Results: mx.google.com; spf=pass (google.com: domain of yang.shi@linux.alibaba.com designates 47.88.44.36 as permitted sender) smtp.mailfrom=yang.shi@linux.alibaba.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R241e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0TSXa0AK_1558676276; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TSXa0AK_1558676276) by smtp.aliyun-inc.com(127.0.0.1); Fri, 24 May 2019 13:37:56 +0800 Subject: Re: [v4 PATCH 1/2] mm: vmscan: remove double slab pressure by inc'ing sc->nr_scanned To: Hillf Danton Cc: ying.huang@intel.com, hannes@cmpxchg.org, mhocko@suse.com, mgorman@techsingularity.net, kirill.shutemov@linux.intel.com, josef@toxicpanda.com, hughd@google.com, shakeelb@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190524041545.10820-1-hdanton@sina.com> From: Yang Shi Message-ID: <6a3a7a59-fe63-68b9-cec1-400395a2a199@linux.alibaba.com> Date: Fri, 24 May 2019 13:37:56 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20190524041545.10820-1-hdanton@sina.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 5/24/19 12:15 PM, Hillf Danton wrote: > On Thu, 23 May 2019 10:27:37 +0800 Yang Shi wrote: >> The commit 9092c71bb724 ("mm: use sc->priority for slab shrink targets") >> has broken up the relationship between sc->nr_scanned and slab pressure. >> The sc->nr_scanned can't double slab pressure anymore. So, it sounds no >> sense to still keep sc->nr_scanned inc'ed. Actually, it would prevent >> from adding pressure on slab shrink since excessive sc->nr_scanned would >> prevent from scan->priority raise. >> > The deleted code below wants to get more slab pages shrinked, and it can do > that without raising scan priority first even after commit 9092c71bb724. Or > we may face the risk that priority goes up too much faster than thought, per > the following snippet. The priority is raised if kswapd_shrink_node() returns false for kswapd (The direct reclaim would just raise the priority if sc->nr_reclaimed >= sc->nr_to_reclaim). The kswapd_shrink_node() returns "return sc->nr_scanned >= sc->nr_to_reclaim". So, the old "double pressure" doesn't work as it was designed anymore since it would prevent from make "sc->nr_scanned < sc->nr_to_reclaim". And, the patch 2/2 would not make the priority go up too much since one THP would be accounted as 512 base page. > > /* > * If we're getting trouble reclaiming, start doing > * writepage even in laptop mode. > */ > if (sc->priority < DEF_PRIORITY - 2) > >> The bonnie test doesn't show this would change the behavior of >> slab shrinkers. >> >> w/ w/o >> /sec %CP /sec %CP >> Sequential delete: 3960.6 94.6 3997.6 96.2 >> Random delete: 2518 63.8 2561.6 64.6 >> >> The slight increase of "/sec" without the patch would be caused by the >> slight increase of CPU usage. >> >> Cc: Josef Bacik >> Cc: Michal Hocko >> Acked-by: Johannes Weiner >> Signed-off-by: Yang Shi >> --- >> v4: Added Johannes's ack >> >> mm/vmscan.c | 5 ----- >> 1 file changed, 5 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 7acd0af..b65bc50 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1137,11 +1137,6 @@ static unsigned long shrink_page_list(struct list_head *page_list, >> if (!sc->may_unmap && page_mapped(page)) >> goto keep_locked; >> >> - /* Double the slab pressure for mapped and swapcache pages */ >> - if ((page_mapped(page) || PageSwapCache(page)) && >> - !(PageAnon(page) && !PageSwapBacked(page))) >> - sc->nr_scanned++; >> - >> may_enter_fs = (sc->gfp_mask & __GFP_FS) || >> (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); >> >> -- >> 1.8.3.1 >> > Best Regards > Hillf