From cf53e99d192171a58791136d33fd3fea5d8bab35 Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Thu, 2 Oct 2014 09:04:01 +1000 Subject: [PATCH] xfs: Don't use xfs_buf_iowait in the delwri buffer code For the special case of delwri buffer submission and waiting, we don't need to issue IO synchronously at all. The second pass to call xfs_buf_iowait() can be replaced with blocking on xfs_buf_lock() - the buffer will be unlocked when the async IO is complete. This formalises a sane the method of waiting for async IO - take an extra reference, submit the IO, call xfs_buf_lock() when you want to wait for IO completion. i.e.: bp = xfs_buf_find(); xfs_buf_hold(bp); bp->b_flags |= XBF_ASYNC; xfs_buf_iosubmit(bp); xfs_buf_lock(bp) error = bp->b_error; .... xfs_buf_relse(bp); While this is somewhat racy for gathering IO errors, none of the code that calls xfs_buf_delwri_submit() will race against other users of the buffers being submitted. Even if they do, we don't really care if the error is detected by the delwri code or the user we raced against. Either way, the error will be detected and handled. Signed-off-by: Dave Chinner Reviewed-by: Christoph Hellwig Signed-off-by: Dave Chinner --- fs/xfs/xfs_buf.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index cd7b8ca9b064..9dc4c2223035 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -1813,12 +1813,17 @@ __xfs_buf_delwri_submit( blk_start_plug(&plug); list_for_each_entry_safe(bp, n, io_list, b_list) { bp->b_flags &= ~(_XBF_DELWRI_Q | XBF_ASYNC | XBF_WRITE_FAIL); - bp->b_flags |= XBF_WRITE; + bp->b_flags |= XBF_WRITE | XBF_ASYNC; - if (!wait) { - bp->b_flags |= XBF_ASYNC; + /* + * we do all Io submission async. This means if we need to wait + * for IO completion we need to take an extra reference so the + * buffer is still valid on the other side. + */ + if (wait) + xfs_buf_hold(bp); + else list_del_init(&bp->b_list); - } xfs_bdstrat_cb(bp); } blk_finish_plug(&plug); @@ -1866,7 +1871,10 @@ xfs_buf_delwri_submit( bp = list_first_entry(&io_list, struct xfs_buf, b_list); list_del_init(&bp->b_list); - error2 = xfs_buf_iowait(bp); + + /* locking the buffer will wait for async IO completion. */ + xfs_buf_lock(bp); + error2 = bp->b_error; xfs_buf_relse(bp); if (!error) error = error2; -- 2.39.5