On 30.08.24 22:28, Barry Song wrote:
From: Barry Song <v-songbaohua@xxxxxxxx>
Three points for this change:
1. We should consolidate all warnings in one place. Currently, the
order > 1 warning is in the hotpath, while others are in less
likely scenarios. Moving all warnings to the slowpath will reduce
the overhead for order > 1 and increase the visibility of other
warnings.
2. We currently have two warnings for order: one for order > 1 in
the hotpath and another for order > costly_order in the laziest
path. I suggest standardizing on order > 1 since it’s been in
use for a long time.
3. We don't need to check for __GFP_NOWARN in this case. __GFP_NOWARN
is meant to suppress allocation failure reports, but here we're
dealing with bug detection, not allocation failures. So replace
WARN_ON_ONCE_GFP by WARN_ON_ONCE.
Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
mm/page_alloc.c | 50 ++++++++++++++++++++++++-------------------------
1 file changed, 25 insertions(+), 25 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c81ee5662cc7..e790b4227322 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3033,12 +3033,6 @@ struct page *rmqueue(struct zone *preferred_zone,
{
struct page *page;
- /*
- * We most definitely don't want callers attempting to
- * allocate greater than order-1 page units with __GFP_NOFAIL.
- */
- WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
-
if (likely(pcp_allowed_order(order))) {
page = rmqueue_pcplist(preferred_zone, zone, order,
migratetype, alloc_flags);
@@ -4175,6 +4169,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
{
bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM;
bool can_compact = gfp_compaction_allowed(gfp_mask);
+ bool nofail = gfp_mask & __GFP_NOFAIL;
const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER;
struct page *page = NULL;
unsigned int alloc_flags;
@@ -4187,6 +4182,25 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
unsigned int zonelist_iter_cookie;
int reserve_flags;
+ if (unlikely(nofail)) {
+ /*
+ * We most definitely don't want callers attempting to
+ * allocate greater than order-1 page units with __GFP_NOFAIL.
+ */
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Should we also clarify that in the docs? Currently we have "Using this
flag for costly allocations is _highly_ discouraged."
We'd likely want to say something like "Allocating pages from the buddy
with __GFP_NOFAIL and order > 1 is not supported."
--
Cheers,
David / dhildenb
