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Mon, 10 Aug 2020 20:44:56 -0800 Received: from MTKMBS02N1.mediatek.inc (172.21.101.77) by MTKMBS62N1.mediatek.inc (172.29.193.41) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Mon, 10 Aug 2020 21:44:55 -0700 Received: from MTKCAS06.mediatek.inc (172.21.101.30) by mtkmbs02n1.mediatek.inc (172.21.101.77) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 11 Aug 2020 12:44:46 +0800 Received: from mtkswgap22.mediatek.inc (172.21.77.33) by MTKCAS06.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Tue, 11 Aug 2020 12:44:46 +0800 From: Chinwen Chang To: Matthias Brugger , Michel Lespinasse , Andrew Morton , "Vlastimil Babka" , Daniel Jordan , "Davidlohr Bueso" , Chinwen Chang , "Alexey Dobriyan" , "Matthew Wilcox (Oracle)" , Jason Gunthorpe , Steven Price , Song Liu , Jimmy Assarsson , Huang Ying Subject: [PATCH 2/2] mm: proc: smaps_rollup: do not stall write attempts on mmap_lock Date: Tue, 11 Aug 2020 12:42:35 +0800 Message-ID: <1597120955-16495-3-git-send-email-chinwen.chang@mediatek.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1597120955-16495-1-git-send-email-chinwen.chang@mediatek.com> References: <1597120955-16495-1-git-send-email-chinwen.chang@mediatek.com> MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200811_004502_408238_11D1D95B X-CRM114-Status: GOOD ( 16.79 ) X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.4 on merlin.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.0 SPF_PASS SPF: sender matches SPF record 0.0 MIME_BASE64_TEXT RAW: Message text disguised using base64 encoding -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.0 UNPARSEABLE_RELAY Informational: message has unparseable relay lines X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fsdevel@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, wsd_upstream@mediatek.com Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org smaps_rollup will try to grab mmap_lock and go through the whole vma list until it finishes the iterating. When encountering large processes, the mmap_lock will be held for a longer time, which may block other write requests like mmap and munmap from progressing smoothly. There are upcoming mmap_lock optimizations like range-based locks, but the lock applied to smaps_rollup would be the coarse type, which doesn't avoid the occurrence of unpleasant contention. To solve aforementioned issue, we add a check which detects whether anyone wants to grab mmap_lock for write attempts. Signed-off-by: Chinwen Chang --- fs/proc/task_mmu.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index dbda449..4b51f25 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -856,6 +856,27 @@ static int show_smaps_rollup(struct seq_file *m, void *v) for (vma = priv->mm->mmap; vma; vma = vma->vm_next) { smap_gather_stats(vma, &mss); last_vma_end = vma->vm_end; + + /* + * Release mmap_lock temporarily if someone wants to + * access it for write request. + */ + if (mmap_lock_is_contended(mm)) { + mmap_read_unlock(mm); + ret = mmap_read_lock_killable(mm); + if (ret) { + release_task_mempolicy(priv); + goto out_put_mm; + } + + /* Check whether current vma is available */ + vma = find_vma(mm, last_vma_end - 1); + if (vma && vma->vm_start < last_vma_end) + continue; + + /* Current vma is not available, just break */ + break; + } } show_vma_header_prefix(m, priv->mm->mmap->vm_start,