lkml.org 
[lkml]   [2009]   [Jan]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: ext2 + -osync: not as easy as it seems
From
Date
On Fri, 2009-01-16 at 00:45 +0100, Jan Kara wrote:
> On Thu 15-01-09 21:06:51, Fernando Luis Vázquez Cao wrote:
> > On Wed, 2009-01-14 at 11:59 -0500, Theodore Tso wrote:
> > > On Wed, Jan 14, 2009 at 03:37:56PM +0100, Jan Kara wrote:
> > > > > Um, we have that already; the sync_inode() followed by
> > > > > blkdev_issue_flush() is the path taken by fdatasync(), I do believe.
> > > >
> > > > Maybe ext4-patch-queue changes that area but in Linus's tree I see:
> > > >
> > > > if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
> > > > goto out;
> > > >
> > > > So if we just overwrite some data, we send them to disk via fdatawrite()
> > > > and then we quickly bail out from ext4_sync_file() without doing
> > > > blkdev_issue_flush().
> > >
> > > So you're thinking about fdatawrite() being called by some code path
> > > other than ext4_sync_file() before we call fsync()? Yeah, that could
> > > happen.... I think that will only happen if the file is opened
> > > O_SYNC, but that raises another issue, which is that we're not forcing
> > > a flush for writes when the file is opened O_SYNC.
> >
> > Hi Jan, Ted
> >
> > Is something like the patch below what you had in mind?
> >
> > --
> >
> > From: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
> > Subject: ext3: call blkdev_issue_flush on fsync
> >
> > To ensure that bits are truly on-disk after an fsync or fdatasync, we
> > should call blkdev_issue_flush if barriers are supported.
> >
> > Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
> > ---
> >
> > --- linux-2.6.29-rc1-orig/fs/ext4/fsync.c 2008-12-25 08:26:37.000000000 +0900
> > +++ linux-2.6.29-rc1/fs/ext4/fsync.c 2009-01-15 21:03:19.000000000 +0900
> > @@ -48,6 +48,7 @@ int ext4_sync_file(struct file *file, st
> > {
> > struct inode *inode = dentry->d_inode;
> > journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
> > + unsigned long i_state = inode->i_state;
> > int ret = 0;
> >
> > J_ASSERT(ext4_journal_current_handle() == NULL);
> > @@ -79,22 +80,35 @@ int ext4_sync_file(struct file *file, st
> > goto out;
> > }
> >
> > - if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
> > - goto out;
> > + if (datasync && !(i_state & I_DIRTY_DATASYNC))
> > + goto flush_blkdev;
> >
> > /*
> > * The VFS has written the file data. If the inode is unaltered
> > * then we need not start a commit.
> > */
> > - if (inode->i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC)) {
> > + if (i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC)) {
> > struct writeback_control wbc = {
> > .sync_mode = WB_SYNC_ALL,
> > .nr_to_write = 0, /* sys_fsync did this */
> > };
> > ret = sync_inode(inode, &wbc);
> > - if (journal && (journal->j_flags & JBD2_BARRIER))
> > - blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
> > + /*
> > + * When there are no blocks attached to the journal transaction
> > + * some optimizations are possible, but if there were dirty
> > + * pages sync_inode() should have ensured that all data gets
> > + * actually written to disk. Thus, we can skip
> > + * blkdev_issue_flush() below.
> > + */
> > + if (!(i_state & I_DIRTY_PAGES))
> > + goto flush_blkdev;
> Uh. Here I don't get it. When we did sync_inode(), blkdev_issue_flush()
> is needed only if the journal does not do barriers. So I'd expect here:
> if (!(journal->j_flags & JBD2_BARRIER))
> goto flush_blkdev;
> goto out;

Ups, you are right. I somehow managed to mangle the logic that I
intended to put here and under flush_blkdev. By the way, I think that
the same check may be needed for the data==journal case too.

Thank you for the feedback, Jan.

I'll be replying to this email with new patches for ext2/ext3.

- Fernando

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2009-01-16 13:33    [W:0.081 / U:0.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site