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Subject[PATCH v3 3/4] limit nr_dentries per superblock
Date
This patch lays the foundation for us to limit the dcache size.
Each super block can have only a maximum amount of dentries under its
sub-tree. Allocation fails if we we're over limit and the cache
can't be pruned to free up space for the newcomers.

Signed-off-by: Glauber Costa <glommer@parallels.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Eric Dumazet <eric.dumazet@gmail.com>
---
fs/dcache.c | 28 ++++++++++++++++++++++++++++
fs/super.c | 1 +
include/linux/fs.h | 1 +
3 files changed, 30 insertions(+), 0 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 815d9fd..ddd02a2 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1180,6 +1180,31 @@ void shrink_dcache_parent(struct dentry * parent)
}
EXPORT_SYMBOL(shrink_dcache_parent);

+static inline int dcache_mem_check(struct super_block *sb)
+{
+ struct shrink_control sc = {
+ .gfp_mask = GFP_KERNEL,
+ };
+
+ if (sb->s_nr_dentry_max == INT_MAX)
+ return 0;
+
+ do {
+ int nr_dentry;
+
+ nr_dentry = percpu_counter_read_positive(&sb->s_nr_dentry);
+ if (nr_dentry > sb->s_nr_dentry_max)
+ nr_dentry =
+ percpu_counter_sum_positive(&sb->s_nr_dentry);
+ if (nr_dentry < sb->s_nr_dentry_max)
+ return 0;
+
+ /* nr_pages = 1, lru_pages = 0 should get delta ~ 2 */
+ } while (shrink_one_shrinker(&sb->s_shrink, &sc, 1, 0));
+
+ return -ENOMEM;
+}
+
/**
* __d_alloc - allocate a dcache entry
* @sb: filesystem it will belong to
@@ -1195,6 +1220,9 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
struct dentry *dentry;
char *dname;

+ if (dcache_mem_check(sb))
+ return NULL;
+
dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
if (!dentry)
return NULL;
diff --git a/fs/super.c b/fs/super.c
index e95ac4f..3db40fb 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -121,6 +121,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
}

percpu_counter_init(&s->s_nr_dentry, 0);
+ s->s_nr_dentry_max = INT_MAX;

#ifdef CONFIG_SMP
s->s_files = alloc_percpu(struct list_head);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8150f52..bc773c3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1400,6 +1400,7 @@ struct super_block {
int s_nr_dentry_unused; /* # of dentry on lru */

struct percpu_counter s_nr_dentry; /* # of dentry on this sb */
+ int s_nr_dentry_max; /* max # of dentry on this sb*/

/* s_inode_lru_lock protects s_inode_lru and s_nr_inodes_unused */
spinlock_t s_inode_lru_lock ____cacheline_aligned_in_smp;
--
1.7.6


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