mm-page_alloc-use-try_cmpxchg-in-set_pfnblock_flags_mask.patch removed from -mm tree

The quilt patch titled
Subject: mm/page_alloc: use try_cmpxchg in set_pfnblock_flags_mask
has been removed from the -mm tree. Its filename was
mm-page_alloc-use-try_cmpxchg-in-set_pfnblock_flags_mask.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Uros Bizjak <[email protected]>
Subject: mm/page_alloc: use try_cmpxchg in set_pfnblock_flags_mask
Date: Fri, 8 Jul 2022 16:07:36 +0200

Use try_cmpxchg instead of cmpxchg in set_pfnblock_flags_mask. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). The main loop improves from:

    1c5d:	48 89 c2             	mov    %rax,%rdx
    1c60:	48 89 c1             	mov    %rax,%rcx
    1c63:	48 21 fa             	and    %rdi,%rdx
    1c66:	4c 09 c2             	or     %r8,%rdx
    1c69:	f0 48 0f b1 16       	lock cmpxchg %rdx,(%rsi)
    1c6e:	48 39 c1             	cmp    %rax,%rcx
    1c71:	75 ea                	jne    1c5d <...>

to:

    1c60:	48 89 ca             	mov    %rcx,%rdx
    1c63:	48 21 c2             	and    %rax,%rdx
    1c66:	4c 09 c2             	or     %r8,%rdx
    1c69:	f0 48 0f b1 16       	lock cmpxchg %rdx,(%rsi)
    1c6e:	75 f0                	jne    1c60 <...>

---

 mm/page_alloc.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

@@ -602,7 +602,7 @@ void set_pfnblock_flags_mask(struct page
 {
 	unsigned long *bitmap;
 	unsigned long bitidx, word_bitidx;
-	unsigned long old_word, word;
+	unsigned long word;
 
 	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
 	BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits));

@@ -618,12 +618,8 @@ void set_pfnblock_flags_mask(struct page
 	flags <<= bitidx;
 
 	word = READ_ONCE(bitmap[word_bitidx]);
-	for (;;) {
-		old_word = cmpxchg(&bitmap[word_bitidx], word, (word & ~mask) | flags);
-		if (word == old_word)
-			break;
-		word = old_word;
-	}
+	do {
+	} while (!try_cmpxchg(&bitmap[word_bitidx], &word, (word & ~mask) | flags));
 }
 
 void set_pageblock_migratetype(struct page *page, int migratetype)

_

Patches currently in -mm which might be from [email protected] are

compiler-gcch-remove-ancient-workaround-for-gcc-pr-58670.patch