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Subject[RFC v2 13/34] mm, slub: do initial checks in ___slab_alloc() with irqs enabled
Date
As another step of shortening irq disabled sections in ___slab_alloc(), delay
disabling irqs until we pass the initial checks if there is a cached percpu
slab and it's suitable for our allocation.

Now we have to recheck c->page after actually disabling irqs as an allocation
in irq handler might have replaced it.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
---
mm/slub.c | 41 ++++++++++++++++++++++++++++++++---------
1 file changed, 32 insertions(+), 9 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 4800d768d0d3..22b5bfef8aa6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2622,8 +2622,9 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,

stat(s, ALLOC_SLOWPATH);

- local_irq_save(flags);
- page = c->page;
+reread_page:
+
+ page = READ_ONCE(c->page);
if (!page) {
/*
* if the node is not online or has no normal memory, just
@@ -2632,6 +2633,11 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
if (unlikely(node != NUMA_NO_NODE &&
!node_isset(node, slab_nodes)))
node = NUMA_NO_NODE;
+ local_irq_save(flags);
+ if (unlikely(c->page)) {
+ local_irq_restore(flags);
+ goto reread_page;
+ }
goto new_slab;
}
redo:
@@ -2646,8 +2652,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
goto redo;
} else {
stat(s, ALLOC_NODE_MISMATCH);
- deactivate_slab(s, page, c->freelist, c);
- goto new_slab;
+ goto deactivate_slab;
}
}

@@ -2656,12 +2661,15 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
* PFMEMALLOC but right now, we are losing the pfmemalloc
* information when the page leaves the per-cpu allocator
*/
- if (unlikely(!pfmemalloc_match(page, gfpflags))) {
- deactivate_slab(s, page, c->freelist, c);
- goto new_slab;
- }
+ if (unlikely(!pfmemalloc_match(page, gfpflags)))
+ goto deactivate_slab;

- /* must check again c->freelist in case of cpu migration or IRQ */
+ /* must check again c->page in case IRQ handler changed it */
+ local_irq_save(flags);
+ if (unlikely(page != c->page)) {
+ local_irq_restore(flags);
+ goto reread_page;
+ }
freelist = c->freelist;
if (freelist)
goto load_freelist;
@@ -2677,6 +2685,9 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
stat(s, ALLOC_REFILL);

load_freelist:
+
+ lockdep_assert_irqs_disabled();
+
/*
* freelist is pointing to the list of objects to be used.
* page is pointing to the page from which the objects are obtained.
@@ -2688,11 +2699,23 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
local_irq_restore(flags);
return freelist;

+deactivate_slab:
+
+ local_irq_save(flags);
+ if (page != c->page) {
+ local_irq_restore(flags);
+ goto reread_page;
+ }
+ deactivate_slab(s, page, c->freelist, c);
+
new_slab:

+ lockdep_assert_irqs_disabled();
+
if (slub_percpu_partial(c)) {
page = c->page = slub_percpu_partial(c);
slub_set_percpu_partial(c, page);
+ local_irq_restore(flags);
stat(s, CPU_PARTIAL_ALLOC);
goto redo;
}
--
2.31.1
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