mm/page_alloc: avoid second trylock of zone->lock

JIRA: https://issues.redhat.com/browse/RHEL-78202

commit c5bb27e
Author: Alexei Starovoitov <ast@kernel.org>
Date:   Sun Mar 30 17:28:09 2025 -0700

    mm/page_alloc: avoid second trylock of zone->lock

    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: 97769a5 ("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>

Signed-off-by: Gregory Bell <grbell@redhat.com>

Author: Gbell26

mm/page_alloc.c

@@ -1264,11 +1264,12 @@ static void free_one_page(struct zone *zone, struct page *page,
 	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);
 	}
 
@@ -2336,9 +2337,10 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
 	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) {
@@ -2959,9 +2961,10 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *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)