From: Tao Ma Subject: Re: [RFC][PATCH 3/3] ext4: add dio overwrite nolock Date: Wed, 02 May 2012 14:59:34 +0800 Message-ID: <4FA0DB56.5000803@tao.ma> References: <1335584346-8070-1-git-send-email-wenqing.lz@taobao.com> <1335584346-8070-4-git-send-email-wenqing.lz@taobao.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org To: Zheng Liu Return-path: Received: from oproxy1-pub.bluehost.com ([66.147.249.253]:36537 "HELO oproxy1-pub.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751185Ab2EBG7l (ORCPT ); Wed, 2 May 2012 02:59:41 -0400 In-Reply-To: <1335584346-8070-4-git-send-email-wenqing.lz@taobao.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 04/28/2012 11:39 AM, Zheng Liu wrote: > From: Zheng Liu > > Aligned and overwrite direct IO can be parallelized. In ext4_file_dio_write, > we first check whether these conditions are satisfied or not. If so, we unlock > the i_mutex and acquire i_data_sem directly. Meanwhile iocb->private is set to > indicate that this is a overwrite dio, and it will be processed in > ext4_ext_direct_IO. > > Signed-off-by: Zheng Liu > --- > fs/ext4/file.c | 140 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- > 1 files changed, 137 insertions(+), 3 deletions(-) > > diff --git a/fs/ext4/file.c b/fs/ext4/file.c > index e5d6be3..8a5f713 100644 > --- a/fs/ext4/file.c > +++ b/fs/ext4/file.c > @@ -100,9 +100,21 @@ static ssize_t > ext4_file_dio_write(struct kiocb *iocb, const struct iovec *iov, > unsigned long nr_segs, loff_t pos) > { > - struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode; > - int unaligned_aio = 0; > + struct file *file = iocb->ki_filp; > + struct address_space * mapping = file->f_mapping; > + struct inode *inode = file->f_path.dentry->d_inode; > + struct blk_plug plug; > ssize_t ret; > + ssize_t written, written_buffered; > + size_t length = iov_length(iov, nr_segs); > + size_t ocount; /* original count */ > + size_t count; /* after file limit checks */ > + int unaligned_aio = 0; > + int overwrite = 0; > + loff_t *ppos = &iocb->ki_pos; > + loff_t endbyte; > + > + BUG_ON(iocb->ki_pos != pos); > > if (!is_sync_kiocb(iocb)) > unaligned_aio = ext4_unaligned_aio(inode, iov, nr_segs, pos); > @@ -121,7 +133,129 @@ ext4_file_dio_write(struct kiocb *iocb, const struct iovec *iov, > ext4_aiodio_wait(inode); > } > > - ret = generic_file_aio_write(iocb, iov, nr_segs, pos); > + mutex_lock(&inode->i_mutex); > + blk_start_plug(&plug); > + > + ocount = 0; > + ret = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ); > + if (ret) > + goto unlock_out; > + > + count = ocount; > + pos = *ppos; > + > + vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE); > + > + /* We can write back this queue in page reclaim */ > + current->backing_dev_info = mapping->backing_dev_info; > + written = 0; > + > + ret = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode)); > + if (ret) > + goto out; > + > + if (count == 0) > + goto out; > + > + ret = file_remove_suid(file); > + if (ret) > + goto out; > + > + file_update_time(file); > + > + iocb->private = NULL; > + > + if (!unaligned_aio && !file->f_mapping->nrpages && > + pos + length < i_size_read(inode) && should be pos + length <= ? And inode->i_size should be ok since now we have i_mutex held. > + ext4_should_dioread_nolock(inode)) { > + struct ext4_map_blocks map; > + unsigned int blkbits = inode->i_blkbits; > + int err; > + int len; > + > + map.m_lblk = pos >> blkbits; > + map.m_len = (EXT4_BLOCK_ALIGN(pos + length, blkbits) >> blkbits) > + - map.m_lblk; > + len = map.m_len; > + > + err = ext4_map_blocks(NULL, inode, &map, 0); > + if (err == len && (!map.m_flags || > + map.m_flags & EXT4_MAP_MAPPED)) { could you please add some comments about how and why map.m_flags are checked this way? > + overwrite = 1; > + iocb->private = &overwrite; > + mutex_unlock(&inode->i_mutex); > + down_read(&EXT4_I(inode)->i_data_sem); Is there any possibility that the metadata is changed after we dropped the i_mutex before the down_read? > + } > + } > + > + if (file->f_mapping->nrpages && overwrite) { > + overwrite = 0; > + up_read(&EXT4_I(inode)->i_data_sem); > + mutex_lock(&inode->i_mutex); I am not sure whether it could happen. But if it does happen, should we also change the value in iocb->private? > + } > + > + written = generic_file_direct_write(iocb, iov, &nr_segs, pos, > + ppos, count, ocount); > + if (written < 0 || written == count) > + goto out; > + /* > + * direct-io write to a hole: fall through to buffered I/O > + * for completing the rest of the request. > + */ > + pos += written; > + count -= written; > + written_buffered = generic_file_buffered_write(iocb, iov, > + nr_segs, pos, ppos, count, > + written); If we fall back here, should we re-lock the i_mutex since the buffer write isn't guaranteed? Thanks Tao > + /* > + * If generic_file_buffered_write() retuned a synchronous error > + * then we want to return the number of bytes which were > + * direct-written, or the error code if that was zero. Note > + * that this differs from normal direct-io semantics, which > + * will return -EFOO even if some bytes were written. > + */ > + if (written_buffered < 0) { > + ret = written_buffered; > + goto out; > + } > + > + /* > + * We need to ensure that the page cache pages are written to > + * disk and invalidated to preserve the expected O_DIRECT > + * semantics. > + */ > + endbyte = pos + written_buffered - written - 1; > + ret = filemap_write_and_wait_range(file->f_mapping, pos, endbyte); > + if (ret == 0) { > + written = written_buffered; > + invalidate_mapping_pages(mapping, > + pos >> PAGE_CACHE_SHIFT, > + endbyte >> PAGE_CACHE_SHIFT); > + } else { > + /* > + * We don't know how much we wrote, so just return > + * the number of bytes which were direct-written > + */ > + } > + > +out: > + current->backing_dev_info = NULL; > + ret = written ? written : ret; > + > +unlock_out: > + if (overwrite) > + up_read(&EXT4_I(inode)->i_data_sem); > + else > + mutex_unlock(&inode->i_mutex); > + > + if (ret > 0 || ret == -EIOCBQUEUED) { > + ssize_t err; > + > + err = generic_write_sync(file, pos, ret); > + if (err < 0 && ret > 0) > + ret = err; > + } > + blk_finish_plug(&plug); > > if (unaligned_aio) > mutex_unlock(ext4_aio_mutex(inode));