+ mm-rmap-use-atomic_try_cmpxchg-in-set_tlb_ubc_flush_pending.patch added to mm-unstable branch

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

The patch titled
     Subject: mm/rmap: use atomic_try_cmpxchg in set_tlb_ubc_flush_pending
has been added to the -mm mm-unstable branch.  Its filename is
     mm-rmap-use-atomic_try_cmpxchg-in-set_tlb_ubc_flush_pending.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-rmap-use-atomic_try_cmpxchg-in-set_tlb_ubc_flush_pending.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
Subject: mm/rmap: use atomic_try_cmpxchg in set_tlb_ubc_flush_pending
Date: Mon, 27 Feb 2023 22:42:28 +0100

Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in set_tlb_ubc_flush_pending.  86 CMPXCHG instruction returns success in
ZF flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails.

No functional change intended.

Link: https://lkml.kernel.org/r/20230227214228.3533299-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---


--- a/mm/rmap.c~mm-rmap-use-atomic_try_cmpxchg-in-set_tlb_ubc_flush_pending
+++ a/mm/rmap.c
@@ -644,7 +644,7 @@ void try_to_unmap_flush_dirty(void)
 static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
 {
 	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
-	int batch, nbatch;
+	int batch;
 
 	arch_tlbbatch_add_mm(&tlb_ubc->arch, mm);
 	tlb_ubc->flush_required = true;
@@ -662,11 +662,8 @@ retry:
 		 * overflow.  Reset `pending' and `flushed' to be 1 and 0 if
 		 * `pending' becomes large.
 		 */
-		nbatch = atomic_cmpxchg(&mm->tlb_flush_batched, batch, 1);
-		if (nbatch != batch) {
-			batch = nbatch;
+		if (!atomic_try_cmpxchg(&mm->tlb_flush_batched, &batch, 1))
 			goto retry;
-		}
 	} else {
 		atomic_inc(&mm->tlb_flush_batched);
 	}
_

Patches currently in -mm which might be from ubizjak@xxxxxxxxx are

mm-rmap-use-atomic_try_cmpxchg-in-set_tlb_ubc_flush_pending.patch
nfs-remove-empty-if-statement-from-nfs3_prepare_get_acl.patch