Since v4.19 commit b0dedc49a2da ("mm/vmscan.c: iterate only over charged shrinkers during memcg shrink_slab()") a memcg aware shrinker is only called when the per-memcg per-node shrinker_map indicates that the shrinker may have objects to release to the memcg and node.
shmem_unused_huge_count and shmem_unused_huge_scan support the per-tmpfs shrinker which advertises per memcg and numa awareness. The shmem shrinker releases memory by splitting hugepages that extend beyond i_size.
Shmem does not currently set bits in shrinker_map. So, starting with b0dedc49a2da, memcg reclaim avoids calling the shmem shrinker under pressure. This leads to undeserved memcg OOM kills. Example that reliably sees memcg OOM kill in unpatched kernel: FS=/tmp/fs CONTAINER=/cgroup/memory/tmpfs_shrinker mkdir -p $FS mount -t tmpfs -o huge=always nodev $FS # Create 1000 MB container, which shouldn't suffer OOM. mkdir $CONTAINER echo 1000M > $CONTAINER/memory.limit_in_bytes echo $BASHPID >> $CONTAINER/cgroup.procs # Create 4000 files. Ideally each file uses 4k data page + a little # metadata. Assume 8k total per-file, 32MB (4000*8k) should easily # fit within container's 1000 MB. But if data pages use 2MB # hugepages (due to aggressive huge=always) then files consume 8GB, # which hits memcg 1000 MB limit. for i in {1..4000}; do echo . > $FS/$i done
v5.4 commit 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware") maintains the per-node per-memcg shrinker bitmap for THP shrinker. But there's no such logic in shmem. Make shmem set the per-memcg per-node shrinker bits when it modifies inodes to have shrinkable pages.
Fixes: b0dedc49a2da ("mm/vmscan.c: iterate only over charged shrinkers during memcg shrink_slab()") Cc: stable@vger.kernel.org # 4.19+ Signed-off-by: Greg Thelen gthelen@google.com --- mm/shmem.c | 61 +++++++++++++++++++++++++++++++----------------------- 1 file changed, 35 insertions(+), 26 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c index bd8840082c94..e11090f78cb5 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1002,6 +1002,33 @@ static int shmem_getattr(const struct path *path, struct kstat *stat, return 0; }
+/* + * Expose inode and optional page to shrinker as having a possibly splittable + * hugepage that reaches beyond i_size. + */ +static void shmem_shrinker_add(struct shmem_sb_info *sbinfo, + struct inode *inode, struct page *page) +{ + struct shmem_inode_info *info = SHMEM_I(inode); + + spin_lock(&sbinfo->shrinklist_lock); + /* + * _careful to defend against unlocked access to ->shrink_list in + * shmem_unused_huge_shrink() + */ + if (list_empty_careful(&info->shrinklist)) { + list_add_tail(&info->shrinklist, &sbinfo->shrinklist); + sbinfo->shrinklist_len++; + } + spin_unlock(&sbinfo->shrinklist_lock); + +#ifdef CONFIG_MEMCG + if (page && PageTransHuge(page)) + memcg_set_shrinker_bit(page->mem_cgroup, page_to_nid(page), + inode->i_sb->s_shrink.id); +#endif +} + static int shmem_setattr(struct dentry *dentry, struct iattr *attr) { struct inode *inode = d_inode(dentry); @@ -1048,17 +1075,13 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr) * to shrink under memory pressure. */ if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { - spin_lock(&sbinfo->shrinklist_lock); - /* - * _careful to defend against unlocked access to - * ->shrink_list in shmem_unused_huge_shrink() - */ - if (list_empty_careful(&info->shrinklist)) { - list_add_tail(&info->shrinklist, - &sbinfo->shrinklist); - sbinfo->shrinklist_len++; - } - spin_unlock(&sbinfo->shrinklist_lock); + struct page *page; + + page = find_get_page(inode->i_mapping, + (newsize & HPAGE_PMD_MASK) >> PAGE_SHIFT); + shmem_shrinker_add(sbinfo, inode, page); + if (page) + put_page(page); } } } @@ -1889,21 +1912,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, if (PageTransHuge(page) && DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE) < hindex + HPAGE_PMD_NR - 1) { - /* - * Part of the huge page is beyond i_size: subject - * to shrink under memory pressure. - */ - spin_lock(&sbinfo->shrinklist_lock); - /* - * _careful to defend against unlocked access to - * ->shrink_list in shmem_unused_huge_shrink() - */ - if (list_empty_careful(&info->shrinklist)) { - list_add_tail(&info->shrinklist, - &sbinfo->shrinklist); - sbinfo->shrinklist_len++; - } - spin_unlock(&sbinfo->shrinklist_lock); + shmem_shrinker_add(sbinfo, inode, page); }
/*