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List:       linux-stable-commits
Subject:    Patch "fs: buffer: do not use unnecessary atomic operations when discarding buffers" has been added 
From:       <gregkh () linuxfoundation ! org>
Date:       2015-01-28 1:00:10
Message-ID: 142240681010233 () kroah ! com
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This is a note to let you know that I've just added the patch titled

    fs: buffer: do not use unnecessary atomic operations when discarding buffers

to the 3.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From e7470ee89f003634a88e7b5e5a7b65b3025987de Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Wed, 4 Jun 2014 16:10:29 -0700
Subject: fs: buffer: do not use unnecessary atomic operations when discarding buffers

From: Mel Gorman <mgorman@suse.de>

commit e7470ee89f003634a88e7b5e5a7b65b3025987de upstream.

Discarding buffers uses a bunch of atomic operations when discarding
buffers because ......  I can't think of a reason.  Use a cmpxchg loop to
clear all the necessary flags.  In most (all?) cases this will be a single
atomic operations.

[akpm@linux-foundation.org: move BUFFER_FLAGS_DISCARD into the .c file]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/buffer.c |   21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1485,16 +1485,27 @@ EXPORT_SYMBOL(set_bh_page);
 /*
  * Called when truncating a buffer on a page completely.
  */
+
+/* Bits that are cleared during an invalidate */
+#define BUFFER_FLAGS_DISCARD \
+	(1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
+	 1 << BH_Delay | 1 << BH_Unwritten)
+
 static void discard_buffer(struct buffer_head * bh)
 {
+	unsigned long b_state, b_state_old;
+
 	lock_buffer(bh);
 	clear_buffer_dirty(bh);
 	bh->b_bdev = NULL;
-	clear_buffer_mapped(bh);
-	clear_buffer_req(bh);
-	clear_buffer_new(bh);
-	clear_buffer_delay(bh);
-	clear_buffer_unwritten(bh);
+	b_state = bh->b_state;
+	for (;;) {
+		b_state_old = cmpxchg(&bh->b_state, b_state,
+				      (b_state & ~BUFFER_FLAGS_DISCARD));
+		if (b_state_old == b_state)
+			break;
+		b_state = b_state_old;
+	}
 	unlock_buffer(bh);
 }
 


Patches currently in stable-queue which might be from mgorman@suse.de are

queue-3.14/mm-page_alloc-use-jump-labels-to-avoid-checking-number_of_cpusets.patch
queue-3.14/mm-page_alloc-do-not-treat-a-zone-that-cannot-be-used-for-dirty-pages-as-full.patch
queue-3.14/mm-non-atomically-mark-page-accessed-during-page-cache-allocation-where-possible.patch
queue-3.14/mm-page_alloc-convert-hot-cold-parameter-and-immediate-callers-to-bool.patch
queue-3.14/mm-page_alloc-only-check-the-zone-id-check-if-pages-are-buddies.patch
queue-3.14/mm-page_alloc-only-check-the-alloc-flags-and-gfp_mask-for-dirty-once.patch
queue-3.14/mm-page_alloc-do-not-update-zlc-unless-the-zlc-is-active.patch
queue-3.14/mm-swap.c-clean-up-lru_cache_add-functions.patch
queue-3.14/mm-page_alloc-take-the-alloc_no_watermark-check-out-of-the-fast-path.patch
queue-3.14/fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers.patch
queue-3.14/mm-do-not-use-atomic-operations-when-releasing-pages.patch
queue-3.14/mm-page_alloc-reduce-number-of-times-page_to_pfn-is-called.patch
queue-3.14/mm-page_alloc-use-unsigned-int-for-order-in-more-places.patch
queue-3.14/mm-shmem-avoid-atomic-operation-during-shmem_getpage_gfp.patch
queue-3.14/mm-do-not-use-unnecessary-atomic-operations-when-adding-pages-to-the-lru.patch
queue-3.14/include-linux-jump_label.h-expose-the-reference-count.patch
queue-3.14/mm-page_alloc-calculate-classzone_idx-once-from-the.patch
queue-3.14/mm-page_alloc-lookup-pageblock-migratetype-with-irqs-enabled-during-free.patch
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