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Date: Tue, 25 May 2021 01:39:42 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Christoph Lameter <cl@...ux.com>,
David Rientjes <rientjes@...gle.com>,
Pekka Enberg <penberg@...nel.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>,
Mel Gorman <mgorman@...hsingularity.net>,
Jesper Dangaard Brouer <brouer@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Jann Horn <jannh@...gle.com>, Vlastimil Babka <vbabka@...e.cz>
Subject: [RFC 22/26] mm, slub: detach percpu partial list in unfreeze_partials() using this_cpu_cmpxchg()
Instead of relying on disabled irqs for atomicity when detaching the percpu
partial list, we can use this_cpu_cmpxchg() and detach without irqs disabled.
However, unfreeze_partials() can be also called from another cpu on behalf of
a cpu that is being offlined, so we need to restructure the code accordingly:
- __unfreeze_partials() is the bulk of unfreeze_partials() that processes the
detached percpu partial list
- unfreeze_partials() uses this_cpu_cmpxchg() to detach list from current cpu
- unfreeze_partials_cpu() is to be called for the offlined cpu so it needs no
protection, and is called from __flush_cpu_slab()
- flush_cpu_slab() needs to call unfreeze_partial() so it can't simply call
__flush_cpu_slab(smp_processor_id()) anymore
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
mm/slub.c | 79 +++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 56 insertions(+), 23 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 414cc621d655..92345d3840d1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2301,25 +2301,15 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
}
}
-/*
- * Unfreeze all the cpu partial slabs.
- *
- * This function must be called with preemption or migration
- * disabled with c local to the cpu.
- */
-static void unfreeze_partials(struct kmem_cache *s,
- struct kmem_cache_cpu *c)
-{
#ifdef CONFIG_SLUB_CPU_PARTIAL
+static void __unfreeze_partials(struct kmem_cache *s, struct page *partial_page)
+{
struct kmem_cache_node *n = NULL, *n2 = NULL;
- struct page *page, *partial_page, *discard_page = NULL;
+ struct page *page, *discard_page = NULL;
unsigned long flags;
local_irq_save(flags);
- partial_page = slub_percpu_partial(c);
- c->partial = NULL;
-
while (partial_page) {
struct page new;
struct page old;
@@ -2374,10 +2364,49 @@ static void unfreeze_partials(struct kmem_cache *s,
discard_slab(s, page);
stat(s, FREE_SLAB);
}
+}
-#endif /* CONFIG_SLUB_CPU_PARTIAL */
+/*
+ * Unfreeze all the cpu partial slabs.
+ *
+ * This function must be called with preemption or migration
+ * disabled.
+ */
+static void unfreeze_partials(struct kmem_cache *s)
+{
+ struct page *partial_page;
+
+ do {
+ partial_page = this_cpu_read(s->cpu_slab->partial);
+
+ } while (partial_page &&
+ this_cpu_cmpxchg(s->cpu_slab->partial, partial_page, NULL)
+ != partial_page);
+
+ if (partial_page)
+ __unfreeze_partials(s, partial_page);
}
+static void unfreeze_partials_cpu(struct kmem_cache *s,
+ struct kmem_cache_cpu *c)
+{
+ struct page *partial_page;
+
+ partial_page = slub_percpu_partial(c);
+ c->partial = NULL;
+
+ if (partial_page)
+ __unfreeze_partials(s, partial_page);
+}
+
+#else /* CONFIG_SLUB_CPU_PARTIAL */
+
+static void unfreeze_partials(struct kmem_cache *s) { }
+static void unfreeze_partials_cpu(struct kmem_cache *s,
+ struct kmem_cache_cpu *c) { }
+
+#endif /* CONFIG_SLUB_CPU_PARTIAL */
+
/*
* Put a page that was just frozen (in __slab_free|get_partial_node) into a
* partial page slot if available.
@@ -2406,7 +2435,7 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
* partial array is full. Move the existing
* set to the per node partial list.
*/
- unfreeze_partials(s, this_cpu_ptr(s->cpu_slab));
+ unfreeze_partials(s);
oldpage = NULL;
pobjects = 0;
pages = 0;
@@ -2424,7 +2453,7 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
} while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page)
!= oldpage);
if (unlikely(!slub_cpu_partial(s)))
- unfreeze_partials(s, this_cpu_ptr(s->cpu_slab));
+ unfreeze_partials(s);
preempt_enable();
#endif /* CONFIG_SLUB_CPU_PARTIAL */
@@ -2444,11 +2473,6 @@ static inline void flush_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)
stat(s, CPUSLAB_FLUSH);
}
-/*
- * Flush cpu slab.
- *
- * Called from IPI handler with interrupts disabled.
- */
static inline void __flush_cpu_slab(struct kmem_cache *s, int cpu)
{
struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
@@ -2456,14 +2480,23 @@ static inline void __flush_cpu_slab(struct kmem_cache *s, int cpu)
if (c->page)
flush_slab(s, c);
- unfreeze_partials(s, c);
+ unfreeze_partials_cpu(s, c);
}
+/*
+ * Flush cpu slab.
+ *
+ * Called from IPI handler with interrupts disabled.
+ */
static void flush_cpu_slab(void *d)
{
struct kmem_cache *s = d;
+ struct kmem_cache_cpu *c = this_cpu_ptr(s->cpu_slab);
- __flush_cpu_slab(s, smp_processor_id());
+ if (c->page)
+ flush_slab(s, c);
+
+ unfreeze_partials(s);
}
static bool has_cpu_slab(int cpu, void *info)
--
2.31.1
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