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Fri, 14 Aug 2020 22:31:06 -0800 Received: from MTKMBS02N1.mediatek.inc (172.21.101.77) by MTKMBS62N2.mediatek.inc (172.29.193.42) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 14 Aug 2020 23:21:06 -0700 Received: from mtkcas07.mediatek.inc (172.21.101.84) by mtkmbs02n1.mediatek.inc (172.21.101.77) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Sat, 15 Aug 2020 14:20:52 +0800 Received: from mtkswgap22.mediatek.inc (172.21.77.33) by mtkcas07.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Sat, 15 Aug 2020 14:20:54 +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 , Daniel Kiss , Laurent Dufour Subject: [PATCH v3 3/3] mm: proc: smaps_rollup: do not stall write attempts on mmap_lock Date: Sat, 15 Aug 2020 14:20:19 +0800 Message-ID: <1597472419-32314-4-git-send-email-chinwen.chang@mediatek.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1597472419-32314-1-git-send-email-chinwen.chang@mediatek.com> References: <1597472419-32314-1-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-20200815_023110_162803_865272DE X-CRM114-Status: GOOD ( 21.13 ) 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_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record 0.0 MIME_BASE64_TEXT RAW: Message text disguised using base64 encoding -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 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. Change since v1: - If current VMA is freed after dropping the lock, it will return - incomplete result. To fix this issue, refine the code flow as - suggested by Steve. [1] Change since v2: - When getting back the mmap lock, the address where you stopped last - time could now be in the middle of a vma. Add one more check to handle - this case as suggested by Michel. [2] [1] https://lore.kernel.org/lkml/bf40676e-b14b-44cd-75ce-419c70194783@arm.com/ [2] https://lore.kernel.org/lkml/CANN689FtCsC71cjAjs0GPspOhgo_HRj+diWsoU1wr98YPktgWg@mail.gmail.com/ Signed-off-by: Chinwen Chang CC: Steven Price CC: Michel Lespinasse Reviewed-by: Steven Price --- fs/proc/task_mmu.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 70 insertions(+), 3 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 76e623a..945904e 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -846,7 +846,7 @@ static int show_smaps_rollup(struct seq_file *m, void *v) struct mem_size_stats mss; struct mm_struct *mm; struct vm_area_struct *vma; - unsigned long last_vma_end = 0; + unsigned long last_vma_end = 0, last_stopped = 0; int ret = 0; priv->task = get_proc_task(priv->inode); @@ -867,9 +867,76 @@ static int show_smaps_rollup(struct seq_file *m, void *v) hold_task_mempolicy(priv); - for (vma = priv->mm->mmap; vma; vma = vma->vm_next) { - smap_gather_stats(vma, &mss, 0); + for (vma = priv->mm->mmap; vma;) { + smap_gather_stats(vma, &mss, last_stopped); + last_stopped = 0; 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; + } + + /* + * After dropping the lock, there are four cases to + * consider. See the following example for explanation. + * + * +------+------+-----------+ + * | VMA1 | VMA2 | VMA3 | + * +------+------+-----------+ + * | | | | + * 4k 8k 16k 400k + * + * Suppose we drop the lock after reading VMA2 due to + * contention, then we get: + * + * last_vma_end = 16k + * + * 1) VMA2 is freed, but VMA3 exists: + * + * find_vma(mm, 16k - 1) will return VMA3. + * In this case, just continue from VMA3. + * + * 2) VMA2 still exists: + * + * find_vma(mm, 16k - 1) will return VMA2. + * Iterate the loop like the original one. + * + * 3) No more VMAs can be found: + * + * find_vma(mm, 16k - 1) will return NULL. + * No more things to do, just break. + * + * 4) (last_vma_end - 1) is the middle of a vma (VMA'): + * + * find_vma(mm, 16k - 1) will return VMA' whose range + * contains last_vma_end. + * Iterate VMA' from last_vma_end. + */ + vma = find_vma(mm, last_vma_end - 1); + /* Case 3 above */ + if (!vma) + break; + + /* Case 1 above */ + if (vma->vm_start >= last_vma_end) + continue; + + /* Case 4 above */ + if (vma->vm_end > last_vma_end) { + last_stopped = last_vma_end; + continue; + } + } + /* Case 2 above */ + vma = vma->vm_next; } show_vma_header_prefix(m, priv->mm->mmap->vm_start,