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Subject[PATCH 2/3] mm/slub: improve consistency of nr_slabs count
Date
Currently, discard_slab() can change nr_slabs count
without holding node's list_lock. This will lead some
error messages print when scanning node's partial or
full list, e.g. validate all slabs. Literally, it
affects the consistency of nr_slabs count.

Here, discard_slab() is abandoned, And dec_slabs_node()
is called before releasing node's list_lock.
dec_slabs_nodes() and free_slab() can be called separately
to ensure consistency of nr_slabs count.

Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com>
---
mm/slub.c | 26 ++++++++++++++------------
1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 310e56d99116..bffb95bbb0ee 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2039,12 +2039,6 @@ static void free_slab(struct kmem_cache *s, struct slab *slab)
__free_slab(s, slab);
}

-static void discard_slab(struct kmem_cache *s, struct slab *slab)
-{
- dec_slabs_node(s, slab_nid(slab), slab->objects);
- free_slab(s, slab);
-}
-
/*
* Management of partially allocated slabs.
*/
@@ -2413,6 +2407,7 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,

if (!new.inuse && n->nr_partial >= s->min_partial) {
mode = M_FREE;
+ spin_lock_irqsave(&n->list_lock, flags);
} else if (new.freelist) {
mode = M_PARTIAL;
/*
@@ -2437,7 +2432,7 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
old.freelist, old.counters,
new.freelist, new.counters,
"unfreezing slab")) {
- if (mode == M_PARTIAL || mode == M_FULL)
+ if (mode != M_FULL_NOLIST)
spin_unlock_irqrestore(&n->list_lock, flags);
goto redo;
}
@@ -2449,7 +2444,10 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
stat(s, tail);
} else if (mode == M_FREE) {
stat(s, DEACTIVATE_EMPTY);
- discard_slab(s, slab);
+ dec_slabs_node(s, slab_nid(slab), slab->objects);
+ spin_unlock_irqrestore(&n->list_lock, flags);
+
+ free_slab(s, slab);
stat(s, FREE_SLAB);
} else if (mode == M_FULL) {
add_full(s, n, slab);
@@ -2502,6 +2500,7 @@ static void __unfreeze_partials(struct kmem_cache *s, struct slab *partial_slab)
if (unlikely(!new.inuse && n->nr_partial >= s->min_partial)) {
slab->next = slab_to_discard;
slab_to_discard = slab;
+ dec_slabs_node(s, slab_nid(slab), slab->objects);
} else {
add_partial(n, slab, DEACTIVATE_TO_TAIL);
stat(s, FREE_ADD_PARTIAL);
@@ -2516,7 +2515,7 @@ static void __unfreeze_partials(struct kmem_cache *s, struct slab *partial_slab)
slab_to_discard = slab_to_discard->next;

stat(s, DEACTIVATE_EMPTY);
- discard_slab(s, slab);
+ free_slab(s, slab);
stat(s, FREE_SLAB);
}
}
@@ -3404,9 +3403,10 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
remove_full(s, n, slab);
}

+ dec_slabs_node(s, slab_nid(slab), slab->objects);
spin_unlock_irqrestore(&n->list_lock, flags);
stat(s, FREE_SLAB);
- discard_slab(s, slab);
+ free_slab(s, slab);
}

/*
@@ -4265,6 +4265,7 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
if (!slab->inuse) {
remove_partial(n, slab);
list_add(&slab->slab_list, &discard);
+ dec_slabs_node(s, slab_nid(slab), slab->objects);
} else {
list_slab_objects(s, slab,
"Objects remaining in %s on __kmem_cache_shutdown()");
@@ -4273,7 +4274,7 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
spin_unlock_irq(&n->list_lock);

list_for_each_entry_safe(slab, h, &discard, slab_list)
- discard_slab(s, slab);
+ free_slab(s, slab);
}

bool __kmem_cache_empty(struct kmem_cache *s)
@@ -4595,6 +4596,7 @@ static int __kmem_cache_do_shrink(struct kmem_cache *s)
if (free == slab->objects) {
list_move(&slab->slab_list, &discard);
n->nr_partial--;
+ dec_slabs_node(s, slab_nid(slab), slab->objects);
} else if (free <= SHRINK_PROMOTE_MAX)
list_move(&slab->slab_list, promote + free - 1);
}
@@ -4610,7 +4612,7 @@ static int __kmem_cache_do_shrink(struct kmem_cache *s)

/* Release empty slabs */
list_for_each_entry_safe(slab, t, &discard, slab_list)
- discard_slab(s, slab);
+ free_slab(s, slab);

if (slabs_node(s, node))
ret = 1;
--
2.27.0
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