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Subject[RFC v2 18/34] mm, slub: stop disabling irqs around get_partial()
Date
The function get_partial() does not need to have irqs disabled as a whole. It's
sufficient to convert spin_lock operations to their irq saving/restoring
versions.

As a result, it's now possible to reach the page allocator from the slab
allocator without disabling and re-enabling interrupts on the way.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/slub.c | 22 ++++++++--------------
1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 760080b58957..6f894d1e84d6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1950,11 +1950,12 @@ static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags);
* Try to allocate a partial slab from a specific node.
*/
static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
- struct page **ret_page, gfp_t flags)
+ struct page **ret_page, gfp_t gfpflags)
{
struct page *page, *page2;
void *object = NULL;
unsigned int available = 0;
+ unsigned long flags;
int objects;

/*
@@ -1966,11 +1967,11 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
if (!n || !n->nr_partial)
return NULL;

- spin_lock(&n->list_lock);
+ spin_lock_irqsave(&n->list_lock, flags);
list_for_each_entry_safe(page, page2, &n->partial, slab_list) {
void *t;

- if (!pfmemalloc_match(page, flags))
+ if (!pfmemalloc_match(page, gfpflags))
continue;

t = acquire_slab(s, n, page, object == NULL, &objects);
@@ -1991,7 +1992,7 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
break;

}
- spin_unlock(&n->list_lock);
+ spin_unlock_irqrestore(&n->list_lock, flags);
return object;
}

@@ -2706,8 +2707,10 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
local_irq_restore(flags);
goto reread_page;
}
- if (unlikely(!slub_percpu_partial(c)))
+ if (unlikely(!slub_percpu_partial(c))) {
+ local_irq_restore(flags);
goto new_objects; /* stolen by an IRQ handler */
+ }

page = c->page = slub_percpu_partial(c);
slub_set_percpu_partial(c, page);
@@ -2716,18 +2719,9 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
goto redo;
}

- local_irq_save(flags);
- if (unlikely(c->page)) {
- local_irq_restore(flags);
- goto reread_page;
- }
-
new_objects:

- lockdep_assert_irqs_disabled();
-
freelist = get_partial(s, gfpflags, node, &page);
- local_irq_restore(flags);
if (freelist)
goto check_new_page;

--
2.31.1
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