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Linux 4.6 compat: Fall back to d_prune_aliases() if necessary

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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 <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Closes: #4726
This commit is contained in:
Tim Chase 2016-06-16 10:19:32 -05:00 committed by Brian Behlendorf
parent 46ab35954c
commit 09fb30e5e9
1 changed files with 15 additions and 2 deletions
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17
module/zfs/zfs_vfsops.c
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@ -1050,8 +1050,7 @@ 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
@ -1141,15 +1140,29 @@ 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,