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Date: Tue, 31 Oct 2023 14:07:38 +0000
From: chengming.zhou@...ux.dev
To: vbabka@...e.cz, cl@...ux.com, penberg@...nel.org,
willy@...radead.org
Cc: rientjes@...gle.com, iamjoonsoo.kim@....com,
akpm@...ux-foundation.org, roman.gushchin@...ux.dev,
42.hyeyoo@...il.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, chengming.zhou@...ux.dev,
Chengming Zhou <zhouchengming@...edance.com>
Subject: [RFC PATCH v4 6/9] slub: Delay freezing of partial slabs
From: Chengming Zhou <zhouchengming@...edance.com>
Now we will freeze slabs when moving them out of node partial list to
cpu partial list, this method needs two cmpxchg_double operations:
1. freeze slab (acquire_slab()) under the node list_lock
2. get_freelist() when pick used in ___slab_alloc()
Actually we don't need to freeze when moving slabs out of node partial
list, we can delay freezing to when use slab freelist in ___slab_alloc(),
so we can save one cmpxchg_double().
And there are other good points:
- The moving of slabs between node partial list and cpu partial list
becomes simpler, since we don't need to freeze or unfreeze at all.
- The node list_lock contention would be less, since we don't need to
freeze any slab under the node list_lock.
We can achieve this because there is no concurrent path would manipulate
the partial slab list except the __slab_free() path, which is now
serialized by slab_test_node_partial() under the list_lock.
Since the slab returned by get_partial() interfaces is not frozen anymore
and no freelist is returned in the partial_context, so we need to use the
introduced freeze_slab() to freeze it and get its freelist.
Similarly, the slabs on the CPU partial list are not frozen anymore,
we need to freeze_slab() on it before use.
We can now delete acquire_slab() as it became unused.
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
---
mm/slub.c | 113 +++++++++++-------------------------------------------
1 file changed, 23 insertions(+), 90 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index edf567971679..bcb5b2c4e213 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2234,51 +2234,6 @@ static void *alloc_single_from_new_slab(struct kmem_cache *s,
return object;
}
-/*
- * Remove slab from the partial list, freeze it and
- * return the pointer to the freelist.
- *
- * Returns a list of objects or NULL if it fails.
- */
-static inline void *acquire_slab(struct kmem_cache *s,
- struct kmem_cache_node *n, struct slab *slab,
- int mode)
-{
- void *freelist;
- unsigned long counters;
- struct slab new;
-
- lockdep_assert_held(&n->list_lock);
-
- /*
- * Zap the freelist and set the frozen bit.
- * The old freelist is the list of objects for the
- * per cpu allocation list.
- */
- freelist = slab->freelist;
- counters = slab->counters;
- new.counters = counters;
- if (mode) {
- new.inuse = slab->objects;
- new.freelist = NULL;
- } else {
- new.freelist = freelist;
- }
-
- VM_BUG_ON(new.frozen);
- new.frozen = 1;
-
- if (!__slab_update_freelist(s, slab,
- freelist, counters,
- new.freelist, new.counters,
- "acquire_slab"))
- return NULL;
-
- remove_partial(n, slab);
- WARN_ON(!freelist);
- return freelist;
-}
-
#ifdef CONFIG_SLUB_CPU_PARTIAL
static void put_cpu_partial(struct kmem_cache *s, struct slab *slab, int drain);
#else
@@ -2295,7 +2250,6 @@ static struct slab *get_partial_node(struct kmem_cache *s,
struct partial_context *pc)
{
struct slab *slab, *slab2, *partial = NULL;
- void *object = NULL;
unsigned long flags;
unsigned int partial_slabs = 0;
@@ -2314,7 +2268,7 @@ static struct slab *get_partial_node(struct kmem_cache *s,
continue;
if (IS_ENABLED(CONFIG_SLUB_TINY) || kmem_cache_debug(s)) {
- object = alloc_single_from_partial(s, n, slab,
+ void *object = alloc_single_from_partial(s, n, slab,
pc->orig_size);
if (object) {
partial = slab;
@@ -2324,13 +2278,10 @@ static struct slab *get_partial_node(struct kmem_cache *s,
continue;
}
- object = acquire_slab(s, n, slab, object == NULL);
- if (!object)
- break;
+ remove_partial(n, slab);
if (!partial) {
partial = slab;
- pc->object = object;
stat(s, ALLOC_FROM_PARTIAL);
} else {
put_cpu_partial(s, slab, 0);
@@ -2629,9 +2580,6 @@ static void __unfreeze_partials(struct kmem_cache *s, struct slab *partial_slab)
unsigned long flags = 0;
while (partial_slab) {
- struct slab new;
- struct slab old;
-
slab = partial_slab;
partial_slab = slab->next;
@@ -2644,23 +2592,7 @@ static void __unfreeze_partials(struct kmem_cache *s, struct slab *partial_slab)
spin_lock_irqsave(&n->list_lock, flags);
}
- do {
-
- old.freelist = slab->freelist;
- old.counters = slab->counters;
- VM_BUG_ON(!old.frozen);
-
- new.counters = old.counters;
- new.freelist = old.freelist;
-
- new.frozen = 0;
-
- } while (!__slab_update_freelist(s, slab,
- old.freelist, old.counters,
- new.freelist, new.counters,
- "unfreezing slab"));
-
- if (unlikely(!new.inuse && n->nr_partial >= s->min_partial)) {
+ if (unlikely(!slab->inuse && n->nr_partial >= s->min_partial)) {
slab->next = slab_to_discard;
slab_to_discard = slab;
} else {
@@ -3167,7 +3099,6 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
node = NUMA_NO_NODE;
goto new_slab;
}
-redo:
if (unlikely(!node_match(slab, node))) {
/*
@@ -3243,7 +3174,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
new_slab:
- if (slub_percpu_partial(c)) {
+#ifdef CONFIG_SLUB_CPU_PARTIAL
+ while (slub_percpu_partial(c)) {
local_lock_irqsave(&s->cpu_slab->lock, flags);
if (unlikely(c->slab)) {
local_unlock_irqrestore(&s->cpu_slab->lock, flags);
@@ -3255,12 +3187,22 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
goto new_objects;
}
- slab = c->slab = slub_percpu_partial(c);
+ slab = slub_percpu_partial(c);
slub_set_percpu_partial(c, slab);
local_unlock_irqrestore(&s->cpu_slab->lock, flags);
stat(s, CPU_PARTIAL_ALLOC);
- goto redo;
+
+ if (unlikely(!node_match(slab, node) ||
+ !pfmemalloc_match(slab, gfpflags))) {
+ slab->next = NULL;
+ __unfreeze_partials(s, slab);
+ continue;
+ }
+
+ freelist = freeze_slab(s, slab);
+ goto retry_load_slab;
}
+#endif
new_objects:
@@ -3268,8 +3210,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
pc.orig_size = orig_size;
slab = get_partial(s, node, &pc);
if (slab) {
- freelist = pc.object;
if (kmem_cache_debug(s)) {
+ freelist = pc.object;
/*
* For debug caches here we had to go through
* alloc_single_from_partial() so just store the
@@ -3281,6 +3223,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
return freelist;
}
+ freelist = freeze_slab(s, slab);
goto retry_load_slab;
}
@@ -3682,18 +3625,8 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
was_frozen = new.frozen;
new.inuse -= cnt;
if ((!new.inuse || !prior) && !was_frozen) {
-
- if (kmem_cache_has_cpu_partial(s) && !prior) {
-
- /*
- * Slab was on no list before and will be
- * partially empty
- * We can defer the list move and instead
- * freeze it.
- */
- new.frozen = 1;
-
- } else { /* Needs to be taken off a list */
+ /* Needs to be taken off a list */
+ if (!kmem_cache_has_cpu_partial(s) || prior) {
n = get_node(s, slab_nid(slab));
/*
@@ -3723,9 +3656,9 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
* activity can be necessary.
*/
stat(s, FREE_FROZEN);
- } else if (new.frozen) {
+ } else if (kmem_cache_has_cpu_partial(s) && !prior) {
/*
- * If we just froze the slab then put it onto the
+ * If we started with a full slab then put it onto the
* per cpu partial list.
*/
put_cpu_partial(s, slab, 1);
--
2.20.1
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