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Mon, 5 Oct 2020 10:40:33 +0800 From: Chinwen Chang To: Andrew Morton CC: , , Chinwen Chang Subject: [RESEND, PATCH v4 1/3] mmap locking API: add mmap_lock_is_contended() Date: Mon, 5 Oct 2020 10:40:12 +0800 Message-ID: <1601865614-4918-2-git-send-email-chinwen.chang@mediatek.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1601865614-4918-1-git-send-email-chinwen.chang@mediatek.com> References: <1601865614-4918-1-git-send-email-chinwen.chang@mediatek.com> MIME-Version: 1.0 X-TM-SNTS-SMTP: D30CA0596B5AD6F1FD606A51781A02C96D57DCE086B02B94315380DA50C8B9092000:8 X-MTK: N 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: Add new API to query if someone wants to acquire mmap_lock for write attempts. Using this instead of rwsem_is_contended makes it more tolerant of future changes to the lock type. Change-Id: Idb21478bb0580ba72b9926aba3bbc4b1f75deec2 Signed-off-by: Chinwen Chang Reviewed-by: Steven Price Acked-by: Michel Lespinasse --- include/linux/mmap_lock.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 0707671..18e7eae 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -87,4 +87,9 @@ static inline void mmap_assert_write_locked(struct mm_struct *mm) VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); } +static inline int mmap_lock_is_contended(struct mm_struct *mm) +{ + return rwsem_is_contended(&mm->mmap_lock); +} + #endif /* _LINUX_MMAP_LOCK_H */ From patchwork Mon Oct 5 02:40:13 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chinwen Chang X-Patchwork-Id: 11816043 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id F19496CA for ; 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Mon, 5 Oct 2020 10:40:42 +0800 From: Chinwen Chang To: Andrew Morton CC: , , Chinwen Chang , Michel Lespinasse Subject: [RESEND, PATCH v4 2/3] mm: smaps*: extend smap_gather_stats to support specified beginning Date: Mon, 5 Oct 2020 10:40:13 +0800 Message-ID: <1601865614-4918-3-git-send-email-chinwen.chang@mediatek.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1601865614-4918-1-git-send-email-chinwen.chang@mediatek.com> References: <1601865614-4918-1-git-send-email-chinwen.chang@mediatek.com> MIME-Version: 1.0 X-MTK: N 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: Extend smap_gather_stats to support indicated beginning address at which it should start gathering. To achieve the goal, we add a new parameter @start assigned by the caller and try to refactor it for simplicity. If @start is 0, it will use the range of @vma for gathering. Change since v2: - This is a new change to make the retry behavior of smaps_rollup - more complete as suggested by Michel [1] [1] https://lore.kernel.org/lkml/CANN689FtCsC71cjAjs0GPspOhgo_HRj+diWsoU1wr98YPktgWg@mail.gmail.com/ Change-Id: I8652e0ee6c5e93fb56376a68d71ed6cdd8ac10e8 Signed-off-by: Chinwen Chang CC: Michel Lespinasse Reviewed-by: Steven Price --- fs/proc/task_mmu.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index dbda449..76e623a 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -723,9 +723,21 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask, .pte_hole = smaps_pte_hole, }; +/* + * Gather mem stats from @vma with the indicated beginning + * address @start, and keep them in @mss. + * + * Use vm_start of @vma as the beginning address if @start is 0. + */ static void smap_gather_stats(struct vm_area_struct *vma, - struct mem_size_stats *mss) + struct mem_size_stats *mss, unsigned long start) { + const struct mm_walk_ops *ops = &smaps_walk_ops; + + /* Invalid start */ + if (start >= vma->vm_end) + return; + #ifdef CONFIG_SHMEM /* In case of smaps_rollup, reset the value from previous vma */ mss->check_shmem_swap = false; @@ -742,18 +754,20 @@ static void smap_gather_stats(struct vm_area_struct *vma, */ unsigned long shmem_swapped = shmem_swap_usage(vma); - if (!shmem_swapped || (vma->vm_flags & VM_SHARED) || - !(vma->vm_flags & VM_WRITE)) { + if (!start && (!shmem_swapped || (vma->vm_flags & VM_SHARED) || + !(vma->vm_flags & VM_WRITE))) { mss->swap += shmem_swapped; } else { mss->check_shmem_swap = true; - walk_page_vma(vma, &smaps_shmem_walk_ops, mss); - return; + ops = &smaps_shmem_walk_ops; } } #endif /* mmap_lock is held in m_start */ - walk_page_vma(vma, &smaps_walk_ops, mss); + if (!start) + walk_page_vma(vma, ops, mss); + else + walk_page_range(vma->vm_mm, start, vma->vm_end, ops, mss); } #define SEQ_PUT_DEC(str, val) \ @@ -805,7 +819,7 @@ static int show_smap(struct seq_file *m, void *v) memset(&mss, 0, sizeof(mss)); - smap_gather_stats(vma, &mss); + smap_gather_stats(vma, &mss, 0); show_map_vma(m, vma); @@ -854,7 +868,7 @@ 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); + smap_gather_stats(vma, &mss, 0); last_vma_end = vma->vm_end; } From patchwork Mon Oct 5 02:40:14 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chinwen Chang X-Patchwork-Id: 11816041 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id DEDA992C for ; Mon, 5 Oct 2020 02:40:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8EFCD2078E for ; Mon, 5 Oct 2020 02:40:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mediatek.com header.i=@mediatek.com header.b="YD4ULh4j" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8EFCD2078E Authentication-Results: mail.kernel.org; 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Mon, 5 Oct 2020 10:40:44 +0800 From: Chinwen Chang To: Andrew Morton CC: , , Chinwen Chang , Michel Lespinasse Subject: [RESEND, PATCH v4 3/3] mm: proc: smaps_rollup: do not stall write attempts on mmap_lock Date: Mon, 5 Oct 2020 10:40:14 +0800 Message-ID: <1601865614-4918-4-git-send-email-chinwen.chang@mediatek.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1601865614-4918-1-git-send-email-chinwen.chang@mediatek.com> References: <1601865614-4918-1-git-send-email-chinwen.chang@mediatek.com> MIME-Version: 1.0 X-MTK: N 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: 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] Change since v3: - last_stopped is easily confused with last_vma_end. Replace it with - a direct call to smap_gather_stats(vma, &mss, last_vma_end) as - suggested by Steve. [3] [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/ [3] https://lore.kernel.org/lkml/db0d40e2-72f3-09d5-c162-9c49218f128f@arm.com/ Change-Id: Idcdb6478ccd06a9e5edd4eda9285378e961a6b94 Signed-off-by: Chinwen Chang Reviewed-by: Steven Price CC: Michel Lespinasse --- fs/proc/task_mmu.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 65 insertions(+), 1 deletion(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 76e623a..1a80624 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -867,9 +867,73 @@ 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) { + for (vma = priv->mm->mmap; vma;) { smap_gather_stats(vma, &mss, 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) + smap_gather_stats(vma, &mss, last_vma_end); + } + /* Case 2 above */ + vma = vma->vm_next; } show_vma_header_prefix(m, priv->mm->mmap->vm_start,