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Subject[RFC v2 21/34] mm, slub: call deactivate_slab() without disabling irqs
Date
The function is now safe to be called with irqs enabled, so move the calls
outside of irq disabled sections.

When called from ___slab_alloc() -> flush_slab() we have irqs disabled, so to
reenable them before deactivate_slab() we need to open-code flush_slab() in
___slab_alloc() and reenable irqs after modifying the kmem_cache_cpu fields.
But that means a IRQ handler meanwhile might have assigned a new page to
kmem_cache_cpu.page so we have to retry the whole check.

The remaining callers of flush_slab() are the IPI handler which has disabled
irqs anyway, and slub_cpu_dead() which will be dealt with in the following
patch.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/slub.c | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index bba18146def6..a99a254f2410 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2706,8 +2706,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
freelist = c->freelist;
c->page = NULL;
c->freelist = NULL;
- deactivate_slab(s, page, freelist);
local_irq_restore(flags);
+ deactivate_slab(s, page, freelist);

new_slab:

@@ -2775,18 +2775,32 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
*/
goto return_single;

+retry_load_page:
+
local_irq_save(flags);
- if (unlikely(c->page))
- flush_slab(s, c);
+ if (unlikely(c->page)) {
+ void *flush_freelist = c->freelist;
+ struct page *flush_page = c->page;
+
+ c->page = NULL;
+ c->freelist = NULL;
+ c->tid = next_tid(c->tid);
+
+ local_irq_restore(flags);
+
+ deactivate_slab(s, flush_page, flush_freelist);
+
+ stat(s, CPUSLAB_FLUSH);
+
+ goto retry_load_page;
+ }
c->page = page;

goto load_freelist;

return_single:

- local_irq_save(flags);
deactivate_slab(s, page, get_freepointer(s, freelist));
- local_irq_restore(flags);
return freelist;
}

--
2.31.1
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