From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Elder Subject: [PATCH REPOST 2/2] rbd: only get snap context for write requests Date: Thu, 03 Jan 2013 16:54:17 -0600 Message-ID: <50E60C19.9060305@inktank.com> References: <50E60BD0.30408@inktank.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ia0-f182.google.com ([209.85.210.182]:37154 "EHLO mail-ia0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754298Ab3ACWyT (ORCPT ); Thu, 3 Jan 2013 17:54:19 -0500 Received: by mail-ia0-f182.google.com with SMTP id x2so13330939iad.13 for ; Thu, 03 Jan 2013 14:54:19 -0800 (PST) In-Reply-To: <50E60BD0.30408@inktank.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: "ceph-devel@vger.kernel.org" Right now we get the snapshot context for an rbd image (under protection of the header semaphore) for every request processed. There's no need to get the snap context if we're doing a read, so avoid doing so in that case. Note that we no longer need to hold the header semaphore to check the rbd_dev's existence flag. Signed-off-by: Alex Elder --- drivers/block/rbd.c | 36 ++++++++++++++++++++---------------- 1 file changed, 20 insertions(+), 16 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index a3b0d43..fd6a708 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -1331,7 +1331,7 @@ static int rbd_do_op(struct request *rq, } else { opcode = CEPH_OSD_OP_READ; flags = CEPH_OSD_FLAG_READ; - snapc = NULL; + rbd_assert(!snapc); snapid = rbd_dev->spec->snap_id; payload_len = 0; } @@ -1661,22 +1661,25 @@ static void rbd_rq_fn(struct request_queue *q) } spin_unlock_irq(q->queue_lock); - /* Stop writes to a read-only device */ - - result = -EROFS; - if (read_only && rq_data_dir(rq) == WRITE) - goto out_end_request; - - /* Grab a reference to the snapshot context */ - - down_read(&rbd_dev->header_rwsem); - if (atomic_read(&rbd_dev->exists)) { + /* Write requests need a reference to the snapshot context */ + + if (rq_data_dir(rq) == WRITE) { + result = -EROFS; + if (read_only) /* Can't write to a read-only device */ + goto out_end_request; + + /* + * Note that each osd request will take its + * own reference to the snapshot context + * supplied. The reference we take here + * just guarantees the one we provide stays + * valid. + */ + down_read(&rbd_dev->header_rwsem); snapc = ceph_get_snap_context(rbd_dev->header.snapc); + up_read(&rbd_dev->header_rwsem); rbd_assert(snapc != NULL); - } - up_read(&rbd_dev->header_rwsem); - - if (!snapc) { + } else if (!atomic_read(&rbd_dev->exists)) { rbd_assert(rbd_dev->spec->snap_id != CEPH_NOSNAP); dout("request for non-existent snapshot"); result = -ENXIO; @@ -1687,7 +1690,8 @@ static void rbd_rq_fn(struct request_queue *q) blk_rq_pos(rq) * SECTOR_SIZE, blk_rq_bytes(rq), rq->bio); out_end_request: - ceph_put_snap_context(snapc); + if (snapc) + ceph_put_snap_context(snapc); spin_lock_irq(q->queue_lock); if (result < 0) __blk_end_request_all(rq, result); -- 1.7.9.5