list_lru: introduce list_lru_shrink_{count,walk}

Kmem accounting of memcg is unusable now, because it lacks slab shrinker
support.  That means when we hit the limit we will get ENOMEM w/o any
chance to recover.  What we should do then is to call shrink_slab, which
would reclaim old inode/dentry caches from this cgroup.  This is what
this patch set is intended to do.

Basically, it does two things.  First, it introduces the notion of
per-memcg slab shrinker.  A shrinker that wants to reclaim objects per
cgroup should mark itself as SHRINKER_MEMCG_AWARE.  Then it will be
passed the memory cgroup to scan from in shrink_control->memcg.  For
such shrinkers shrink_slab iterates over the whole cgroup subtree under
the target cgroup and calls the shrinker for each kmem-active memory
cgroup.

Secondly, this patch set makes the list_lru structure per-memcg.  It's
done transparently to list_lru users - everything they have to do is to
tell list_lru_init that they want memcg-aware list_lru.  Then the
list_lru will automatically distribute objects among per-memcg lists
basing on which cgroup the object is accounted to.  This way to make FS
shrinkers (icache, dcache) memcg-aware we only need to make them use
memcg-aware list_lru, and this is what this patch set does.

As before, this patch set only enables per-memcg kmem reclaim when the
pressure goes from memory.limit, not from memory.kmem.limit.  Handling
memory.kmem.limit is going to be tricky due to GFP_NOFS allocations, and
it is still unclear whether we will have this knob in the unified
hierarchy.

This patch (of 9):

NUMA aware slab shrinkers use the list_lru structure to distribute
objects coming from different NUMA nodes to different lists.  Whenever
such a shrinker needs to count or scan objects from a particular node,
it issues commands like this:

        count = list_lru_count_node(lru, sc->nid);
        freed = list_lru_walk_node(lru, sc->nid, isolate_func,
                                   isolate_arg, &sc->nr_to_scan);

where sc is an instance of the shrink_control structure passed to it
from vmscan.

To simplify this, let's add special list_lru functions to be used by
shrinkers, list_lru_shrink_count() and list_lru_shrink_walk(), which
consolidate the nid and nr_to_scan arguments in the shrink_control
structure.

This will also allow us to avoid patching shrinkers that use list_lru
when we make shrink_slab() per-memcg - all we will have to do is extend
the shrink_control structure to include the target memcg and make
list_lru_shrink_{count,walk} handle this appropriately.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Suggested-by: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Greg Thelen <gthelen@google.com>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

9 files changed, 51 insertions, 43 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index e368d4f412f9..56c5da89f58a 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -930,24 +930,22 @@ dentry_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
 /**
  * prune_dcache_sb - shrink the dcache
  * @sb: superblock
- * @nr_to_scan : number of entries to try to free
- * @nid: which node to scan for freeable entities
+ * @sc: shrink control, passed to list_lru_shrink_walk()
  *
- * Attempt to shrink the superblock dcache LRU by @nr_to_scan entries. This is
- * done when we need more memory an called from the superblock shrinker
+ * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
+ * is done when we need more memory and called from the superblock shrinker
  * function.
  *
  * This function may fail to free any resources if all the dentries are in
  * use.
  */
-long prune_dcache_sb(struct super_block *sb, unsigned long nr_to_scan,
-                     int nid)
+long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
 {
         LIST_HEAD(dispose);
         long freed;
 
-        freed = list_lru_walk_node(&sb->s_dentry_lru, nid, dentry_lru_isolate,
-                                       &dispose, &nr_to_scan);
+        freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
+                                     dentry_lru_isolate, &dispose);
         shrink_dentry_list(&dispose);
         return freed;
 }
diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
index 3e193cb36996..c15d6b216d0b 100644
--- a/fs/gfs2/quota.c
+++ b/fs/gfs2/quota.c
@@ -171,8 +171,8 @@ static unsigned long gfs2_qd_shrink_scan(struct shrinker *shrink,
         if (!(sc->gfp_mask & __GFP_FS))
                 return SHRINK_STOP;
 
-        freed = list_lru_walk_node(&gfs2_qd_lru, sc->nid, gfs2_qd_isolate,
-                                   &dispose, &sc->nr_to_scan);
+        freed = list_lru_shrink_walk(&gfs2_qd_lru, sc,
+                                     gfs2_qd_isolate, &dispose);
 
         gfs2_qd_dispose(&dispose);
 
@@ -182,7 +182,7 @@ static unsigned long gfs2_qd_shrink_scan(struct shrinker *shrink,
 static unsigned long gfs2_qd_shrink_count(struct shrinker *shrink,
                                           struct shrink_control *sc)
 {
-        return vfs_pressure_ratio(list_lru_count_node(&gfs2_qd_lru, sc->nid));
+        return vfs_pressure_ratio(list_lru_shrink_count(&gfs2_qd_lru, sc));
 }
 
 struct shrinker gfs2_qd_shrinker = {
diff --git a/fs/inode.c b/fs/inode.c
index 3a53b1da3fb8..524a32c2b0c6 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -751,14 +751,13 @@ inode_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
  * to trim from the LRU. Inodes to be freed are moved to a temporary list and
  * then are freed outside inode_lock by dispose_list().
  */
-long prune_icache_sb(struct super_block *sb, unsigned long nr_to_scan,
-                     int nid)
+long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
 {
         LIST_HEAD(freeable);
         long freed;
 
-        freed = list_lru_walk_node(&sb->s_inode_lru, nid, inode_lru_isolate,
-                                       &freeable, &nr_to_scan);
+        freed = list_lru_shrink_walk(&sb->s_inode_lru, sc,
+                                     inode_lru_isolate, &freeable);
         dispose_list(&freeable);
         return freed;
 }
diff --git a/fs/internal.h b/fs/internal.h
index e9a61fe67575..d92c346a793d 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -14,6 +14,7 @@ struct file_system_type;
 struct linux_binprm;
 struct path;
 struct mount;
+struct shrink_control;
 
 /*
  * block_dev.c
@@ -111,8 +112,7 @@ extern int open_check_o_direct(struct file *f);
  * inode.c
  */
 extern spinlock_t inode_sb_list_lock;
-extern long prune_icache_sb(struct super_block *sb, unsigned long nr_to_scan,
-                            int nid);
+extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc);
 extern void inode_add_lru(struct inode *inode);
 
 /*
@@ -129,8 +129,7 @@ extern int invalidate_inodes(struct super_block *, bool);
  */
 extern struct dentry *__d_alloc(struct super_block *, const struct qstr *);
 extern int d_set_mounted(struct dentry *dentry);
-extern long prune_dcache_sb(struct super_block *sb, unsigned long nr_to_scan,
-                            int nid);
+extern long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc);
 
 /*
  * read_write.c
diff --git a/fs/super.c b/fs/super.c
index eae088f6aaae..4554ac257647 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -77,8 +77,8 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
         if (sb->s_op->nr_cached_objects)
                 fs_objects = sb->s_op->nr_cached_objects(sb, sc->nid);
 
-        inodes = list_lru_count_node(&sb->s_inode_lru, sc->nid);
-        dentries = list_lru_count_node(&sb->s_dentry_lru, sc->nid);
+        inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
+        dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
         total_objects = dentries + inodes + fs_objects + 1;
         if (!total_objects)
                 total_objects = 1;
@@ -86,20 +86,20 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
         /* proportion the scan between the caches */
         dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
         inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
+        fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
 
         /*
          * prune the dcache first as the icache is pinned by it, then
          * prune the icache, followed by the filesystem specific caches
          */
-        freed = prune_dcache_sb(sb, dentries, sc->nid);
-        freed += prune_icache_sb(sb, inodes, sc->nid);
+        sc->nr_to_scan = dentries;
+        freed = prune_dcache_sb(sb, sc);
+        sc->nr_to_scan = inodes;
+        freed += prune_icache_sb(sb, sc);
 
-        if (fs_objects) {
-                fs_objects = mult_frac(sc->nr_to_scan, fs_objects,
-                                                                total_objects);
+        if (fs_objects)
                 freed += sb->s_op->free_cached_objects(sb, fs_objects,
                                                        sc->nid);
-        }
 
         drop_super(sb);
         return freed;
@@ -118,17 +118,15 @@ static unsigned long super_cache_count(struct shrinker *shrink,
          * scalability bottleneck. The counts could get updated
          * between super_cache_count and super_cache_scan anyway.
          * Call to super_cache_count with shrinker_rwsem held
-         * ensures the safety of call to list_lru_count_node() and
+         * ensures the safety of call to list_lru_shrink_count() and
          * s_op->nr_cached_objects().
          */
         if (sb->s_op && sb->s_op->nr_cached_objects)
                 total_objects = sb->s_op->nr_cached_objects(sb,
                                                  sc->nid);
 
-        total_objects += list_lru_count_node(&sb->s_dentry_lru,
-                                                 sc->nid);
-        total_objects += list_lru_count_node(&sb->s_inode_lru,
-                                                 sc->nid);
+        total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
+        total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
 
         total_objects = vfs_pressure_ratio(total_objects);
         return total_objects;
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index bb502a391792..15c9d224c721 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1583,10 +1583,9 @@ xfs_buftarg_shrink_scan(
                                         struct xfs_buftarg, bt_shrinker);
         LIST_HEAD(dispose);
         unsigned long           freed;
-        unsigned long           nr_to_scan = sc->nr_to_scan;
 
-        freed = list_lru_walk_node(&btp->bt_lru, sc->nid, xfs_buftarg_isolate,
-                                       &dispose, &nr_to_scan);
+        freed = list_lru_shrink_walk(&btp->bt_lru, sc,
+                                     xfs_buftarg_isolate, &dispose);
 
         while (!list_empty(&dispose)) {
                 struct xfs_buf *bp;
@@ -1605,7 +1604,7 @@ xfs_buftarg_shrink_count(
 {
         struct xfs_buftarg      *btp = container_of(shrink,
                                         struct xfs_buftarg, bt_shrinker);
-        return list_lru_count_node(&btp->bt_lru, sc->nid);
+        return list_lru_shrink_count(&btp->bt_lru, sc);
 }
 
 void
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 3e8186279541..4f4b1274e144 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -523,7 +523,6 @@ xfs_qm_shrink_scan(
         struct xfs_qm_isolate   isol;
         unsigned long           freed;
         int                     error;
-        unsigned long           nr_to_scan = sc->nr_to_scan;
 
         if ((sc->gfp_mask & (__GFP_FS|__GFP_WAIT)) != (__GFP_FS|__GFP_WAIT))
                 return 0;
@@ -531,8 +530,8 @@ xfs_qm_shrink_scan(
         INIT_LIST_HEAD(&isol.buffers);
         INIT_LIST_HEAD(&isol.dispose);
 
-        freed = list_lru_walk_node(&qi->qi_lru, sc->nid, xfs_qm_dquot_isolate, &isol,
-                                        &nr_to_scan);
+        freed = list_lru_shrink_walk(&qi->qi_lru, sc,
+                                     xfs_qm_dquot_isolate, &isol);
 
         error = xfs_buf_delwri_submit(&isol.buffers);
         if (error)
@@ -557,7 +556,7 @@ xfs_qm_shrink_count(
         struct xfs_quotainfo    *qi = container_of(shrink,
                                         struct xfs_quotainfo, qi_shrinker);
 
-        return list_lru_count_node(&qi->qi_lru, sc->nid);
+        return list_lru_shrink_count(&qi->qi_lru, sc);
 }
 
 /*
diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index f3434533fbf8..f500a2e39b13 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -9,6 +9,7 @@
 
 #include <linux/list.h>
 #include <linux/nodemask.h>
+#include <linux/shrinker.h>
 
 /* list_lru_walk_cb has to always return one of those */
 enum lru_status {
@@ -81,6 +82,13 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item);
  * Callers that want such a guarantee need to provide an outer lock.
  */
 unsigned long list_lru_count_node(struct list_lru *lru, int nid);
+
+static inline unsigned long list_lru_shrink_count(struct list_lru *lru,
+                                                  struct shrink_control *sc)
+{
+        return list_lru_count_node(lru, sc->nid);
+}
+
 static inline unsigned long list_lru_count(struct list_lru *lru)
 {
         long count = 0;
@@ -120,6 +128,14 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
                                  unsigned long *nr_to_walk);
 
 static inline unsigned long
+list_lru_shrink_walk(struct list_lru *lru, struct shrink_control *sc,
+                     list_lru_walk_cb isolate, void *cb_arg)
+{
+        return list_lru_walk_node(lru, sc->nid, isolate, cb_arg,
+                                  &sc->nr_to_scan);
+}
+
+static inline unsigned long
 list_lru_walk(struct list_lru *lru, list_lru_walk_cb isolate,
               void *cb_arg, unsigned long nr_to_walk)
 {
diff --git a/mm/workingset.c b/mm/workingset.c
index f7216fa7da27..d4fa7fb10a52 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -275,7 +275,7 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
 
         /* list_lru lock nests inside IRQ-safe mapping->tree_lock */
         local_irq_disable();
-        shadow_nodes = list_lru_count_node(&workingset_shadow_nodes, sc->nid);
+        shadow_nodes = list_lru_shrink_count(&workingset_shadow_nodes, sc);
         local_irq_enable();
 
         pages = node_present_pages(sc->nid);
@@ -376,8 +376,8 @@ static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
 
         /* list_lru lock nests inside IRQ-safe mapping->tree_lock */
         local_irq_disable();
-        ret =  list_lru_walk_node(&workingset_shadow_nodes, sc->nid,
-                                  shadow_lru_isolate, NULL, &sc->nr_to_scan);
+        ret =  list_lru_shrink_walk(&workingset_shadow_nodes, sc,
+                                    shadow_lru_isolate, NULL);
         local_irq_enable();
         return ret;
 }