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Re: [PATCH 6/7] ext4: honor the O_SYNC flag for aysnchronous direct I/O

To: Jeff Moyer <jmoyer@xxxxxxxxxx>
Subject: Re: [PATCH 6/7] ext4: honor the O_SYNC flag for aysnchronous direct I/O requests
From: Jan Kara <jack@xxxxxxx>
Date: Mon, 5 Mar 2012 11:09:33 +0100
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, jack@xxxxxxx, hch@xxxxxxxxxxxxx
In-reply-to: <1330718175-21540-7-git-send-email-jmoyer@xxxxxxxxxx>
References: <1330718175-21540-1-git-send-email-jmoyer@xxxxxxxxxx> <1330718175-21540-7-git-send-email-jmoyer@xxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
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@xxxxxxx>

                                                                Honza
> 
> Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
> ---
>  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@xxxxxxx>
SUSE Labs, CR

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