NOTE: this is not about __GFP_THISNODE, this is only about GFP_THISNODE.
GFP_THISNODE is a secret combination of gfp bits that have different
behavior than expected. It is a combination of __GFP_THISNODE,
__GFP_NORETRY, and __GFP_NOWARN and is special-cased in the page allocator
slowpath to fail without trying reclaim even though it may be used in
combination with __GFP_WAIT.
An example of the problem this creates: commit e97ca8e5b864 ("mm: fix
GFP_THISNODE callers and clarify") fixed up many users of GFP_THISNODE
that really just wanted __GFP_THISNODE. The problem doesn't end there,
however, because even it was a no-op for alloc_misplaced_dst_page(),
which also sets __GFP_NORETRY and __GFP_NOWARN, and
migrate_misplaced_transhuge_page(), where __GFP_NORETRY and __GFP_NOWAIT
is set in GFP_TRANSHUGE. Converting GFP_THISNODE to __GFP_THISNODE is
a no-op in these cases since the page allocator special-cases
__GFP_THISNODE && __GFP_NORETRY && __GFP_NOWARN.
It's time to just remove GFP_TRANSHUGE entirely. We leave __GFP_THISNODE
to restrict an allocation to a local node, but remove GFP_TRANSHUGE and
it's obscurity. Instead, we require that a caller clear __GFP_WAIT if it
wants to avoid reclaim.
This allows the aforementioned functions to actually reclaim as they
should. It also enables any future callers that want to do
__GFP_THISNODE but also __GFP_NORETRY && __GFP_NOWARN to reclaim. The
rule is simple: if you don't want to reclaim, then don't set __GFP_WAIT.
Aside: ovs_flow_stats_update() really wants to avoid reclaim as well, so
it is unchanged.
Signed-off-by: David Rientjes <rient...@google.com>
---
include/linux/gfp.h | 10 ----------
mm/page_alloc.c | 22 ++++++----------------
mm/slab.c | 22 ++++++++++++++++++----
net/openvswitch/flow.c | 4 +++-
4 files changed, 27 insertions(+), 31 deletions(-)
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -117,16 +117,6 @@ struct vm_area_struct;
__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN | \
__GFP_NO_KSWAPD)
-/*
- * GFP_THISNODE does not perform any reclaim, you most likely want to
- * use __GFP_THISNODE to allocate from a given node without fallback!
- */
-#ifdef CONFIG_NUMA
-#define GFP_THISNODE (__GFP_THISNODE | __GFP_NOWARN | __GFP_NORETRY)
-#else
-#define GFP_THISNODE ((__force gfp_t)0)
-#endif
-
/* This mask makes up all the page movable related flags */
#define GFP_MOVABLE_MASK (__GFP_RECLAIMABLE|__GFP_MOVABLE)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2355,13 +2355,7 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
/* The OOM killer does not compensate for light reclaim */
if (!(gfp_mask & __GFP_FS))
goto out;
- /*
- * GFP_THISNODE contains __GFP_NORETRY and we never hit this.
- * Sanity check for bare calls of __GFP_THISNODE, not real OOM.
- * The caller should handle page allocation failure by itself if
- * it specifies __GFP_THISNODE.
- * Note: Hugepage uses it but will hit PAGE_ALLOC_COSTLY_ORDER.
- */
+ /* The OOM killer may not free memory on a specific node */
if (gfp_mask & __GFP_THISNODE)
goto out;
}
@@ -2615,15 +2609,11 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int
order,
}
/*
- * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and
- * __GFP_NOWARN set) should not cause reclaim since the subsystem
- * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim
- * using a larger set of nodes after it has established that the
- * allowed per node queues are empty and that nodes are
- * over allocated.
+ * If this allocation cannot block and it is for a specific node, then
+ * fail early. There's no need to wakeup kswapd or retry for a
+ * speculative node-specific allocation.
*/
- if (IS_ENABLED(CONFIG_NUMA) &&
- (gfp_mask & GFP_THISNODE) == GFP_THISNODE)
+ if (IS_ENABLED(CONFIG_NUMA) && (gfp_mask & __GFP_THISNODE) && !wait)
goto nopage;
retry:
@@ -2816,7 +2806,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
/*
* Check the zones suitable for the gfp_mask contain at least one
* valid zone. It's possible to have an empty zonelist as a result
- * of GFP_THISNODE and a memoryless node
+ * of __GFP_THISNODE and a memoryless node
*/
if (unlikely(!zonelist->_zonerefs->zone))
return NULL;
diff --git a/mm/slab.c b/mm/slab.c
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -857,6 +857,11 @@ static inline void *____cache_alloc_node(struct kmem_cache
*cachep,
return NULL;
}
+static inline gfp_t gfp_exact_node(gfp_t flags)
+{
+ return flags;
+}
+
#else /* CONFIG_NUMA */
static void *____cache_alloc_node(struct kmem_cache *, gfp_t, int);
@@ -1023,6 +1028,15 @@ static inline int cache_free_alien(struct kmem_cache
*cachep, void *objp)
return __cache_free_alien(cachep, objp, node, page_node);
}
+
+/*
+ * Construct gfp mask to allocate from a specific node but do not invoke
reclaim
+ * or warn about failures.
+ */
+static inline gfp_t gfp_exact_node(gfp_t flags)
+{
+ return (flags | __GFP_THISNODE | __GFP_NOWARN) & ~__GFP_WAIT;
+}
#endif
/*
@@ -2825,7 +2839,7 @@ alloc_done:
if (unlikely(!ac->avail)) {
int x;
force_grow:
- x = cache_grow(cachep, flags | GFP_THISNODE, node, NULL);
+ x = cache_grow(cachep, gfp_exact_node(flags), node, NULL);
/* cache_grow can reenable interrupts, then ac could change. */
ac = cpu_cache_get(cachep);
@@ -3019,7 +3033,7 @@ retry:
get_node(cache, nid) &&
get_node(cache, nid)->free_objects) {
obj = ____cache_alloc_node(cache,
- flags | GFP_THISNODE, nid);
+ gfp_exact_node(flags), nid);
if (obj)
break;
}
@@ -3047,7 +3061,7 @@ retry:
nid = page_to_nid(page);
if (cache_grow(cache, flags, nid, page)) {
obj = ____cache_alloc_node(cache,
- flags | GFP_THISNODE, nid);
+ gfp_exact_node(flags), nid);
if (!obj)
/*
* Another processor may allocate the
@@ -3118,7 +3132,7 @@ retry:
must_grow:
spin_unlock(&n->list_lock);
- x = cache_grow(cachep, flags | GFP_THISNODE, nodeid, NULL);
+ x = cache_grow(cachep, gfp_exact_node(flags), nodeid, NULL);
if (x)
goto retry;
diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -100,7 +100,9 @@ void ovs_flow_stats_update(struct sw_flow *flow, __be16
tcp_flags,
new_stats =
kmem_cache_alloc_node(flow_stats_cache,
- GFP_THISNODE |
+ GFP_NOWAIT |
+ __GFP_THISNODE |
+ __GFP_NOWARN |
__GFP_NOMEMALLOC,
node);
if (likely(new_stats)) {
--
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