From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mel Gorman , Johannes Weiner , Vlastimil Babka , Jan Kara , Michal Hocko , Hugh Dickins , Dave Hansen , Theodore Tso , "Paul E. McKenney" , Oleg Nesterov , Rik van Riel , Peter Zijlstra , Andrew Morton , Linus Torvalds Subject: [PATCH 3.14 61/77] fs: buffer: do not use unnecessary atomic operations when discarding buffers Date: Tue, 27 Jan 2015 17:27:39 -0800 Message-Id: <20150128012747.796039292@linuxfoundation.org> In-Reply-To: <20150128012745.971137091@linuxfoundation.org> References: <20150128012745.971137091@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mel Gorman 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 Cc: Johannes Weiner Cc: Vlastimil Babka Cc: Jan Kara Cc: Michal Hocko Cc: Hugh Dickins Cc: Dave Hansen Cc: Theodore Ts'o Cc: "Paul E. McKenney" Cc: Oleg Nesterov Cc: Rik van Riel Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman --- 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); }