From: Goldwyn Rodrigues Subject: [PATCH 05/10] fs: return if direct write will trigger writeback Date: Tue, 6 Jun 2017 06:19:34 -0500 Message-ID: <20170606111939.27272-6-rgoldwyn@suse.de> References: <20170606111939.27272-1-rgoldwyn@suse.de> Cc: jack@suse.com, hch@infradead.org, linux-block@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, axboe@kernel.dk, linux-api@vger.kernel.org, adam.manzanares@wdc.com, viro@zeniv.linux.org.uk, Goldwyn Rodrigues To: linux-fsdevel@vger.kernel.org Return-path: In-Reply-To: <20170606111939.27272-1-rgoldwyn@suse.de> Sender: linux-block-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org From: Goldwyn Rodrigues Find out if the write will trigger a wait due to writeback. If yes, return -EAGAIN. Return -EINVAL for buffered AIO: there are multiple causes of delay such as page locks, dirty throttling logic, page loading from disk etc. which cannot be taken care of. Reviewed-by: Christoph Hellwig Reviewed-by: Jan Kara Signed-off-by: Goldwyn Rodrigues --- mm/filemap.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 097213275461..bc146efa6815 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2675,6 +2675,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from) pos = iocb->ki_pos; + if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT)) + return -EINVAL; + if (limit != RLIM_INFINITY) { if (iocb->ki_pos >= limit) { send_sig(SIGXFSZ, current, 0); @@ -2743,9 +2746,17 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from) write_len = iov_iter_count(from); end = (pos + write_len - 1) >> PAGE_SHIFT; - written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1); - if (written) - goto out; + if (iocb->ki_flags & IOCB_NOWAIT) { + /* If there are pages to writeback, return */ + if (filemap_range_has_page(inode->i_mapping, pos, + pos + iov_iter_count(from))) + return -EAGAIN; + } else { + written = filemap_write_and_wait_range(mapping, pos, + pos + write_len - 1); + if (written) + goto out; + } /* * After a write we want buffered reads to be sure to go to disk to get -- 2.12.0