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authorChinwen Chang <chinwen.chang@mediatek.com>2020-10-13 16:53:47 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-10-13 18:38:31 -0700
commitff9f47f6f00cfe1625a06a136e286a47c9483b2e (patch)
tree9c611713b26066a5d652ea1f24ab19cb12e01e40 /fs
parent03b4b1149308b0f0d76075a25d4100f684bef326 (diff)
downloadlinux-stericsson-ff9f47f6f00cfe1625a06a136e286a47c9483b2e.tar.gz
mm: proc: smaps_rollup: do not stall write attempts on mmap_lock
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 <chinwen.chang@mediatek.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Steven Price <steven.price@arm.com> Cc: Michel Lespinasse <walken@google.com> Cc: Matthias Brugger <matthias.bgg@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Daniel Jordan <daniel.m.jordan@oracle.com> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: Chinwen Chang <chinwen.chang@mediatek.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Song Liu <songliubraving@fb.com> Cc: Jimmy Assarsson <jimmyassarsson@gmail.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Daniel Kiss <daniel.kiss@arm.com> Cc: Laurent Dufour <ldufour@linux.ibm.com> Link: http://lkml.kernel.org/r/1597715898-3854-4-git-send-email-chinwen.chang@mediatek.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/proc/task_mmu.c66
1 files changed, 65 insertions, 1 deletions
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index f77727530b9c..846d43df3fdf 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -865,9 +865,73 @@ 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,