Eric Lee / smarc-ti-linux-kernel

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Commit 967e64285aef3670019bd05bef74085d9ea98104

Authored by Mel Gorman
Committed by Jiri Slaby
1 parent 6ffef5d8bf
Exists in ti-linux-3.12.y and in 2 other branches newt-ti-linux-3.12.y, smarc-ti-linux-3.12.y

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

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: Jiri Slaby <jslaby@suse.cz>

Showing 1 changed file with 16 additions and 5 deletions Side-by-side Diff

... ... @@ -1483,16 +1483,27 @@
1483 1483 /*
1484 1484 * Called when truncating a buffer on a page completely.
1485 1485 */
  1486 +
  1487 +/* Bits that are cleared during an invalidate */
  1488 +#define BUFFER_FLAGS_DISCARD \
  1489 + (1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
  1490 + 1 << BH_Delay | 1 << BH_Unwritten)
  1491 +
1486 1492 static void discard_buffer(struct buffer_head * bh)
1487 1493 {
  1494 + unsigned long b_state, b_state_old;
  1495 +
1488 1496 lock_buffer(bh);
1489 1497 clear_buffer_dirty(bh);
1490 1498 bh->b_bdev = NULL;
1491   - clear_buffer_mapped(bh);
1492   - clear_buffer_req(bh);
1493   - clear_buffer_new(bh);
1494   - clear_buffer_delay(bh);
1495   - clear_buffer_unwritten(bh);
  1499 + b_state = bh->b_state;
  1500 + for (;;) {
  1501 + b_state_old = cmpxchg(&bh->b_state, b_state,
  1502 + (b_state & ~BUFFER_FLAGS_DISCARD));
  1503 + if (b_state_old == b_state)
  1504 + break;
  1505 + b_state = b_state_old;
  1506 + }
1496 1507 unlock_buffer(bh);
1497 1508 }
1498 1509