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Mon, 10 Feb 2020 22:20:28 -0800 (PST) Received: from localhost.localdomain ([114.206.198.176]) by smtp.gmail.com with ESMTPSA id x197sm2578696pfc.1.2020.02.10.22.20.25 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 10 Feb 2020 22:20:28 -0800 (PST) From: js1304@gmail.com X-Google-Original-From: iamjoonsoo.kim@lge.com To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Johannes Weiner , Michal Hocko , Hugh Dickins , Minchan Kim , Vlastimil Babka , Mel Gorman , kernel-team@lge.com, Joonsoo Kim Subject: [PATCH 6/9] mm/workingset: handle the page without memcg Date: Tue, 11 Feb 2020 15:19:50 +0900 Message-Id: <1581401993-20041-7-git-send-email-iamjoonsoo.kim@lge.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1581401993-20041-1-git-send-email-iamjoonsoo.kim@lge.com> References: <1581401993-20041-1-git-send-email-iamjoonsoo.kim@lge.com> 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: From: Joonsoo Kim When implementing workingset detection for anonymous page, I found some swapcache pages with NULL memcg. From the code reading, I found two reasons. One is the case that swap-in readahead happens. The other is the corner case related to the shmem cache. These two problems should be fixed, but, it's not straight-forward to fix. For example, when swap-off, all swapped-out pages are read into swapcache. In this case, who's the owner of the swapcache page? Since this problem doesn't look trivial, I decide to leave the issue and handles this corner case on the place where the error occurs. Signed-off-by: Joonsoo Kim --- mm/workingset.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/workingset.c b/mm/workingset.c index 636aafc..20286d6 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -257,6 +257,10 @@ void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg) VM_BUG_ON_PAGE(page_count(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); + /* page_memcg() can be NULL if swap-in readahead happens */ + if (!page_memcg(page)) + return NULL; + advance_inactive_age(page_memcg(page), pgdat, is_file); lruvec = mem_cgroup_lruvec(target_memcg, pgdat);