From: Joonsoo Kim <js1...@gmail.com>
The function get_partial() is currently not checking pfmemalloc_match()
meaning that it is possible for pfmemalloc pages to leak to non-pfmemalloc
users. This is a problem in the following situation. Assume that there is
a request from normal allocation and there are no objects in the per-cpu
cache and no node-partial slab.
In this case, slab_alloc enters the slow path and new_slab_objects()
is called which may return a PFMEMALLOC page. As the current user is not
allowed to access PFMEMALLOC page, deactivate_slab() is called ([5091b74a:
mm: slub: optimise the SLUB fast path to avoid pfmemalloc checks]) and
returns an object from PFMEMALLOC page.
Next time, when we get another request from normal allocation, slab_alloc()
enters the slow-path and calls new_slab_objects(). In new_slab_objects(),
we call get_partial() and get a partial slab which was just deactivated
but is a pfmemalloc page. We extract one object from it and re-deactivate.
"deactivate -> re-get in get_partial -> re-deactivate" occures repeatedly.
As a result, access to PFMEMALLOC page is not properly restricted and it
can cause a performance degradation due to frequent deactivation.
deactivation frequently.
This patch changes get_partial_node() to take pfmemalloc_match() into
account and prevents the "deactivate -> re-get in get_partial() scenario.
Instead, new_slab() is called.
Signed-off-by: Joonsoo Kim <js1...@gmail.com>
Acked-by: David Rientjes <rient...@google.com>
Signed-off-by: Mel Gorman <mgor...@suse.de>
---
mm/slub.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 8f78e25..2fdd96f9e9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1524,12 +1524,13 @@ static inline void *acquire_slab(struct kmem_cache *s,
}
static int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain);
+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 kmem_cache_cpu *c)
+static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
+ struct kmem_cache_cpu *c, gfp_t flags)
{
struct page *page, *page2;
void *object = NULL;
@@ -1545,9 +1546,13 @@ static void *get_partial_node(struct kmem_cache *s,
spin_lock(&n->list_lock);
list_for_each_entry_safe(page, page2, &n->partial, lru) {
- void *t = acquire_slab(s, n, page, object == NULL);
+ void *t;
int available;
+ if (!pfmemalloc_match(page, flags))
+ continue;
+
+ t = acquire_slab(s, n, page, object == NULL);
if (!t)
break;
@@ -1614,7 +1619,7 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t
flags,
if (n && cpuset_zone_allowed_hardwall(zone, flags) &&
n->nr_partial > s->min_partial) {
- object = get_partial_node(s, n, c);
+ object = get_partial_node(s, n, c, flags);
if (object) {
/*
* Return the object even if
@@ -1643,7 +1648,7 @@ static void *get_partial(struct kmem_cache *s, gfp_t
flags, int node,
void *object;
int searchnode = (node == NUMA_NO_NODE) ? numa_node_id() : node;
- object = get_partial_node(s, get_node(s, searchnode), c);
+ object = get_partial_node(s, get_node(s, searchnode), c, flags);
if (object || node != NUMA_NO_NODE)
return object;
--
1.7.9.2
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