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Date: Mon, 5 Mar 2012 11:09:33 +0100
From: Jan Kara <jack@...e.cz>
To: Jeff Moyer <jmoyer@...hat.com>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
xfs@....sgi.com, jack@...e.cz, hch@...radead.org
Subject: Re: [PATCH 6/7] ext4: honor the O_SYNC flag for aysnchronous
direct I/O requests
On Fri 02-03-12 14:56:14, Jeff Moyer wrote:
> Hi,
>
> If a file is opened with O_SYNC|O_DIRECT, the drive cache does not get
> flushed after the write completion. Instead, it's flushed *before* the
> I/O is sent to the disk (in __generic_file_aio_write). This patch
> attempts to fix that problem by marking an I/O as requiring a cache
> flush in endio processing. I'll send a follow-on patch to the
> generic write code to get rid of the bogus generic_write_sync call
> when EIOCBQUEUED is returned.
Looks good. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
>
> Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
> ---
> fs/ext4/ext4.h | 4 +++
> fs/ext4/inode.c | 11 ++++++-
> fs/ext4/page-io.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++-----
> fs/ext4/super.c | 11 ++++++++
> 4 files changed, 90 insertions(+), 9 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 3ce6a0c..e1478be 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -186,6 +186,7 @@ struct mpage_da_data {
> #define EXT4_IO_END_QUEUED 0x0004
> #define EXT4_IO_END_DIRECT 0x0008
> #define EXT4_IO_END_IN_FSYNC 0x0010
> +#define EXT4_IO_END_NEEDS_SYNC 0x0020
>
> struct ext4_io_page {
> struct page *p_page;
> @@ -1248,6 +1249,9 @@ struct ext4_sb_info {
> /* workqueue for dio unwritten */
> struct workqueue_struct *dio_unwritten_wq;
>
> + /* workqueue for aio+dio+o_sync disk cache flushing */
> + struct workqueue_struct *aio_dio_flush_wq;
> +
> /* timer for periodic error stats printing */
> struct timer_list s_err_report;
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index f6dc02b..13cdb4c 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2769,8 +2769,12 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
>
> iocb->private = NULL;
>
> + /* AIO+DIO+O_SYNC I/Os need a cache flush after completion */
> + if (is_async && (IS_SYNC(inode) || (iocb->ki_filp->f_flags & O_DSYNC)))
> + io_end->flag |= EXT4_IO_END_NEEDS_SYNC;
> +
> /* if not aio dio with unwritten extents, just free io and return */
> - if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
> + if (!(io_end->flag & (EXT4_IO_END_UNWRITTEN|EXT4_IO_END_NEEDS_SYNC))) {
> ext4_free_io_end(io_end);
> out:
> if (is_async)
> @@ -2785,7 +2789,10 @@ out:
> io_end->iocb = iocb;
> io_end->result = ret;
> }
> - wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
> + if (io_end->flag & EXT4_IO_END_UNWRITTEN)
> + wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
> + else
> + wq = EXT4_SB(io_end->inode->i_sb)->aio_dio_flush_wq;
>
> /* Add the io_end to per-inode completed aio dio list*/
> ei = EXT4_I(io_end->inode);
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index dcdeef1..baa1b84 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -82,6 +82,50 @@ void ext4_free_io_end(ext4_io_end_t *io)
> }
>
> /*
> + * This function is called in the completion path for AIO O_SYNC|O_DIRECT
> + * writes, and also in the fsync path. The purpose is to ensure that the
> + * disk caches for the journal and data devices are flushed.
> + */
> +static int ext4_end_io_do_flush(ext4_io_end_t *io)
> +{
> + struct inode *inode = io->inode;
> + tid_t commit_tid;
> + bool needs_barrier = false;
> + journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
> + int barriers_enabled = test_opt(inode->i_sb, BARRIER);
> + int ret = 0;
> +
> + if (!barriers_enabled)
> + return 0;
> +
> + /*
> + * If we are running in nojournal mode, just flush the disk
> + * cache and return.
> + */
> + if (!journal)
> + return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL);
> +
> + if (ext4_should_journal_data(inode)) {
> + ret = ext4_force_commit(inode->i_sb);
> + goto out;
> + }
> +
> + commit_tid = io->iocb->ki_filp->f_flags & __O_SYNC ?
> + EXT4_I(inode)->i_sync_tid : EXT4_I(inode)->i_datasync_tid;
> + if (!jbd2_trans_will_send_data_barrier(journal, commit_tid))
> + needs_barrier = true;
> +
> + jbd2_log_start_commit(journal, commit_tid);
> + ret = jbd2_log_wait_commit(journal, commit_tid);
> +
> + if (!ret && needs_barrier)
> + ret = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL);
> +
> +out:
> + return ret;
> +}
> +
> +/*
> * check a range of space and convert unwritten extents to written.
> *
> * Called with inode->i_mutex; we depend on this when we manipulate
> @@ -98,15 +142,30 @@ int ext4_end_io_nolock(ext4_io_end_t *io)
> "list->prev 0x%p\n",
> io, inode->i_ino, io->list.next, io->list.prev);
>
> - ret = ext4_convert_unwritten_extents(inode, offset, size);
> - if (ret < 0) {
> - ext4_msg(inode->i_sb, KERN_EMERG,
> - "failed to convert unwritten extents to written "
> - "extents -- potential data loss! "
> - "(inode %lu, offset %llu, size %zd, error %d)",
> - inode->i_ino, offset, size, ret);
> + if (io->flag & EXT4_IO_END_UNWRITTEN) {
> +
> + ret = ext4_convert_unwritten_extents(inode, offset, size);
> + if (ret < 0) {
> + ext4_msg(inode->i_sb, KERN_EMERG,
> + "failed to convert unwritten extents to "
> + "written extents -- potential data loss! "
> + "(inode %lu, offset %llu, size %zd, error %d)",
> + inode->i_ino, offset, size, ret);
> + goto endio;
> + }
> }
>
> + /*
> + * This function has two callers. The first is the end_io_work
> + * routine just below, which is an asynchronous completion context.
> + * The second is in the fsync path. For the latter path, we can't
> + * return from here until the job is done. Hence,
> + * ext4_end_io_do_flush is blocking.
> + */
> + if (io->flag & EXT4_IO_END_NEEDS_SYNC)
> + ret = ext4_end_io_do_flush(io);
> +
> +endio:
> if (io->iocb)
> aio_complete(io->iocb, io->result, 0);
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 502c61f..a24938e 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -805,6 +805,7 @@ static void ext4_put_super(struct super_block *sb)
> dquot_disable(sb, -1, DQUOT_USAGE_ENABLED | DQUOT_LIMITS_ENABLED);
>
> flush_workqueue(sbi->dio_unwritten_wq);
> + destroy_workqueue(sbi->aio_dio_flush_wq);
> destroy_workqueue(sbi->dio_unwritten_wq);
>
> lock_super(sb);
> @@ -3718,6 +3719,13 @@ no_journal:
> goto failed_mount_wq;
> }
>
> + EXT4_SB(sb)->aio_dio_flush_wq =
> + alloc_workqueue("ext4-aio-dio-flush", WQ_MEM_RECLAIM | WQ_UNBOUND, 1);
> + if (!EXT4_SB(sb)->aio_dio_flush_wq) {
> + printk(KERN_ERR "EXT4-fs: failed to create flush workqueue\n");
> + goto failed_flush_wq;
> + }
> +
> /*
> * The jbd2_journal_load will have done any necessary log recovery,
> * so we can safely mount the rest of the filesystem now.
> @@ -3840,6 +3848,8 @@ failed_mount4a:
> sb->s_root = NULL;
> failed_mount4:
> ext4_msg(sb, KERN_ERR, "mount failed");
> + destroy_workqueue(EXT4_SB(sb)->aio_dio_flush_wq);
> +failed_flush_wq:
> destroy_workqueue(EXT4_SB(sb)->dio_unwritten_wq);
> failed_mount_wq:
> if (sbi->s_journal) {
> @@ -4303,6 +4313,7 @@ static int ext4_sync_fs(struct super_block *sb, int wait)
>
> trace_ext4_sync_fs(sb, wait);
> flush_workqueue(sbi->dio_unwritten_wq);
> + flush_workqueue(sbi->aio_dio_flush_wq);
> if (jbd2_journal_start_commit(sbi->s_journal, &target)) {
> if (wait)
> jbd2_log_wait_commit(sbi->s_journal, target);
> --
> 1.7.1
>
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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