patches/old/mm-page_alloc-avoid-second-trylock-of-zone-lock.patch

From: Alexei Starovoitov <ast@kernel.org>
Subject: mm/page_alloc: avoid second trylock of zone->lock
Date: Sun, 30 Mar 2025 17:28:09 -0700

spin_trylock followed by spin_lock will cause extra write cache access. 
If the lock is contended it may cause unnecessary cache line bouncing and
will execute redundant irq restore/save pair.  Therefore, check
alloc/fpi_flags first and use spin_trylock or spin_lock.

Link: https://lkml.kernel.org/r/20250331002809.94758-1-alexei.starovoitov@gmail.com
Fixes: 97769a53f117 ("mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Daniel Borkman <daniel@iogearbox.net>
Cc: Martin KaFai Lau <martin.lau@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-avoid-second-trylock-of-zone-lock
+++ a/mm/page_alloc.c
@@ -1400,11 +1400,12 @@ static void free_one_page(struct zone *z
 	struct llist_head *llhead;
 	unsigned long flags;
 
-	if (!spin_trylock_irqsave(&zone->lock, flags)) {
-		if (unlikely(fpi_flags & FPI_TRYLOCK)) {
+	if (unlikely(fpi_flags & FPI_TRYLOCK)) {
+		if (!spin_trylock_irqsave(&zone->lock, flags)) {
 			add_page_to_zone_llist(zone, page, order);
 			return;
 		}
+	} else {
 		spin_lock_irqsave(&zone->lock, flags);
 	}
 
@@ -2314,9 +2315,10 @@ static int rmqueue_bulk(struct zone *zon
 	unsigned long flags;
 	int i;
 
-	if (!spin_trylock_irqsave(&zone->lock, flags)) {
-		if (unlikely(alloc_flags & ALLOC_TRYLOCK))
+	if (unlikely(alloc_flags & ALLOC_TRYLOCK)) {
+		if (!spin_trylock_irqsave(&zone->lock, flags))
 			return 0;
+	} else {
 		spin_lock_irqsave(&zone->lock, flags);
 	}
 	for (i = 0; i < count; ++i) {
@@ -2937,9 +2939,10 @@ struct page *rmqueue_buddy(struct zone *
 
 	do {
 		page = NULL;
-		if (!spin_trylock_irqsave(&zone->lock, flags)) {
-			if (unlikely(alloc_flags & ALLOC_TRYLOCK))
+		if (unlikely(alloc_flags & ALLOC_TRYLOCK)) {
+			if (!spin_trylock_irqsave(&zone->lock, flags))
 				return NULL;
+		} else {
 			spin_lock_irqsave(&zone->lock, flags);
 		}
 		if (alloc_flags & ALLOC_HIGHATOMIC)
_