From db3f5edcf1b7df869a064062359ffde83a0175ec Mon Sep 17 00:00:00 2001 From: Tim Chase Date: Thu, 16 Jun 2016 10:19:32 -0500 Subject: [PATCH] Linux 4.6 compat: Fall back to d_prune_aliases() if necessary As of 4.6, the icache and dcache LRUs are memcg aware insofar as the kernel's per-superblock shrinker is concerned. The effect is that dcache or icache entries added by a task in a non-root memcg won't be scanned by the shrinker in the context of the root (or NULL) memcg. This defeats the attempts by zfs_sb_prune() to unpin buffers and can allow metadata to grow uncontrollably. This patch reverts to the d_prune_aliaes() method in case the kernel's per-superblock shrinker is not able to free anything. Signed-off-by: Tim Chase Signed-off-by: Brian Behlendorf Signed-off-by: Chunwei Chen Closes: #4726 --- module/zfs/zfs_vfsops.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/module/zfs/zfs_vfsops.c b/module/zfs/zfs_vfsops.c index 7d8332ac85..5cdb511992 100644 --- a/module/zfs/zfs_vfsops.c +++ b/module/zfs/zfs_vfsops.c @@ -1124,8 +1124,7 @@ zfs_root(zfs_sb_t *zsb, struct inode **ipp) } EXPORT_SYMBOL(zfs_root); -#if !defined(HAVE_SPLIT_SHRINKER_CALLBACK) && !defined(HAVE_SHRINK) && \ - defined(HAVE_D_PRUNE_ALIASES) +#ifdef HAVE_D_PRUNE_ALIASES /* * Linux kernels older than 3.1 do not support a per-filesystem shrinker. * To accommodate this we must improvise and manually walk the list of znodes @@ -1215,15 +1214,29 @@ zfs_sb_prune(struct super_block *sb, unsigned long nr_to_scan, int *objects) } else { *objects = (*shrinker->scan_objects)(shrinker, &sc); } + #elif defined(HAVE_SPLIT_SHRINKER_CALLBACK) *objects = (*shrinker->scan_objects)(shrinker, &sc); #elif defined(HAVE_SHRINK) *objects = (*shrinker->shrink)(shrinker, &sc); #elif defined(HAVE_D_PRUNE_ALIASES) +#define D_PRUNE_ALIASES_IS_DEFAULT *objects = zfs_sb_prune_aliases(zsb, nr_to_scan); #else #error "No available dentry and inode cache pruning mechanism." #endif + +#if defined(HAVE_D_PRUNE_ALIASES) && !defined(D_PRUNE_ALIASES_IS_DEFAULT) +#undef D_PRUNE_ALIASES_IS_DEFAULT + /* + * Fall back to zfs_sb_prune_aliases if the kernel's per-superblock + * shrinker couldn't free anything, possibly due to the inodes being + * allocated in a different memcg. + */ + if (*objects == 0) + *objects = zfs_sb_prune_aliases(zsb, nr_to_scan); +#endif + ZFS_EXIT(zsb); dprintf_ds(zsb->z_os->os_dsl_dataset,