From: Barry Song <[email protected]>
When users allocate memory with the __GFP_NOFAIL flag, they might
incorrectly use it alongside GFP_ATOMIC, GFP_NOWAIT, etc. This kind of
non-blockable __GFP_NOFAIL is not supported and is pointless. If we
attempt and still fail to allocate memory for these users, we have two
choices:
1. We could busy-loop and hope that some other direct reclamation or
kswapd rescues the current process. However, this is unreliable
and could ultimately lead to hard or soft lockups, which might not
be well supported by some architectures.
2. We could use BUG_ON to trigger a reliable system crash, avoiding
exposing NULL dereference.
Neither option is ideal, but both are improvements over the existing code.
This patch selects the second option because, with the introduction of
scoped API and GFP_NOFAIL—capable of enforcing direct reclamation for
nofail users(which is in my plan), non-blockable nofail allocations will
no longer be possible.
Signed-off-by: Barry Song <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Uladzislau Rezki (Sony) <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Hyeonggon Yoo <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: "Eugenio Pérez" <[email protected]>
Cc: Hailong.Liu <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Maxime Coquelin <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Xuan Zhuo <[email protected]>
---
mm/page_alloc.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d2c37f8f8d09..fb5850ecd3ae 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4399,11 +4399,11 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int
order,
*/
if (gfp_mask & __GFP_NOFAIL) {
/*
- * All existing users of the __GFP_NOFAIL are blockable, so warn
- * of any new users that actually require GFP_NOWAIT
+ * All existing users of the __GFP_NOFAIL are blockable
+ * otherwise we introduce a busy loop with inside the page
+ * allocator from non-sleepable contexts
*/
- if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))
- goto fail;
+ BUG_ON(!can_direct_reclaim);
/*
* PF_MEMALLOC request from this context is rather bizarre
@@ -4434,7 +4434,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
cond_resched();
goto retry;
}
-fail:
+
warn_alloc(gfp_mask, ac->nodemask,
"page allocation failure: order:%u", order);
got_pg:
--
2.39.3 (Apple Git-146)
