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authorRoman Gushchin <guro@fb.com>2018-04-10 16:27:44 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-04-11 10:28:29 -0700
commitf1782c9bc547754f4bd3043fe8cfda53db85f13f (patch)
treed5b25e08831e52c5a5d665fdd3b837a653dab21b
parent034ebf65c3c21d85b963d39f992258a64a85e3a9 (diff)
dcache: account external names as indirectly reclaimable memory
I received a report about suspicious growth of unreclaimable slabs on some machines. I've found that it happens on machines with low memory pressure, and these unreclaimable slabs are external names attached to dentries. External names are allocated using generic kmalloc() function, so they are accounted as unreclaimable. But they are held by dentries, which are reclaimable, and they will be reclaimed under the memory pressure. In particular, this breaks MemAvailable calculation, as it doesn't take unreclaimable slabs into account. This leads to a silly situation, when a machine is almost idle, has no memory pressure and therefore has a big dentry cache. And the resulting MemAvailable is too low to start a new workload. To address the issue, the NR_INDIRECTLY_RECLAIMABLE_BYTES counter is used to track the amount of memory, consumed by external names. The counter is increased in the dentry allocation path, if an external name structure is allocated; and it's decreased in the dentry freeing path. To reproduce the problem I've used the following Python script: import os for iter in range (0, 10000000): try: name = ("/some_long_name_%d" % iter) + "_" * 220 os.stat(name) except Exception: pass Without this patch: $ cat /proc/meminfo | grep MemAvailable MemAvailable: 7811688 kB $ python indirect.py $ cat /proc/meminfo | grep MemAvailable MemAvailable: 2753052 kB With the patch: $ cat /proc/meminfo | grep MemAvailable MemAvailable: 7809516 kB $ python indirect.py $ cat /proc/meminfo | grep MemAvailable MemAvailable: 7749144 kB [guro@fb.com: fix indirectly reclaimable memory accounting for CONFIG_SLOB] Link: http://lkml.kernel.org/r/20180312194140.19517-1-guro@fb.com [guro@fb.com: fix indirectly reclaimable memory accounting] Link: http://lkml.kernel.org/r/20180313125701.7955-1-guro@fb.com Link: http://lkml.kernel.org/r/20180305133743.12746-5-guro@fb.com Signed-off-by: Roman Gushchin <guro@fb.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Mel Gorman <mgorman@techsingularity.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/dcache.c39
1 files changed, 30 insertions, 9 deletions
diff --git a/fs/dcache.c b/fs/dcache.c
index 593079176123..915816e90049 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -257,11 +257,25 @@ static void __d_free(struct rcu_head *head)
kmem_cache_free(dentry_cache, dentry);
}
+static void __d_free_external_name(struct rcu_head *head)
+{
+ struct external_name *name = container_of(head, struct external_name,
+ u.head);
+
+ mod_node_page_state(page_pgdat(virt_to_page(name)),
+ NR_INDIRECTLY_RECLAIMABLE_BYTES,
+ -ksize(name));
+
+ kfree(name);
+}
+
static void __d_free_external(struct rcu_head *head)
{
struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
- kfree(external_name(dentry));
- kmem_cache_free(dentry_cache, dentry);
+
+ __d_free_external_name(&external_name(dentry)->u.head);
+
+ kmem_cache_free(dentry_cache, dentry);
}
static inline int dname_external(const struct dentry *dentry)
@@ -291,7 +305,7 @@ void release_dentry_name_snapshot(struct name_snapshot *name)
struct external_name *p;
p = container_of(name->name, struct external_name, name[0]);
if (unlikely(atomic_dec_and_test(&p->u.count)))
- kfree_rcu(p, u.head);
+ call_rcu(&p->u.head, __d_free_external_name);
}
}
EXPORT_SYMBOL(release_dentry_name_snapshot);
@@ -1617,6 +1631,7 @@ EXPORT_SYMBOL(d_invalidate);
struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
{
+ struct external_name *ext = NULL;
struct dentry *dentry;
char *dname;
int err;
@@ -1637,14 +1652,14 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
dname = dentry->d_iname;
} else if (name->len > DNAME_INLINE_LEN-1) {
size_t size = offsetof(struct external_name, name[1]);
- struct external_name *p = kmalloc(size + name->len,
- GFP_KERNEL_ACCOUNT);
- if (!p) {
+
+ ext = kmalloc(size + name->len, GFP_KERNEL_ACCOUNT);
+ if (!ext) {
kmem_cache_free(dentry_cache, dentry);
return NULL;
}
- atomic_set(&p->u.count, 1);
- dname = p->name;
+ atomic_set(&ext->u.count, 1);
+ dname = ext->name;
} else {
dname = dentry->d_iname;
}
@@ -1683,6 +1698,12 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
}
}
+ if (unlikely(ext)) {
+ pg_data_t *pgdat = page_pgdat(virt_to_page(ext));
+ mod_node_page_state(pgdat, NR_INDIRECTLY_RECLAIMABLE_BYTES,
+ ksize(ext));
+ }
+
this_cpu_inc(nr_dentry);
return dentry;
@@ -2770,7 +2791,7 @@ static void copy_name(struct dentry *dentry, struct dentry *target)
dentry->d_name.hash_len = target->d_name.hash_len;
}
if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
- kfree_rcu(old_name, u.head);
+ call_rcu(&old_name->u.head, __d_free_external_name);
}
/*