Re: [PATCH] improve the performance of large sequential write NFS workloads

Trond Myklebust
2009-12-23T19:14:01Z

On Wed, 2009-12-23 at 19:05 +0100, Jan Kara wrote:
> On Wed 23-12-09 15:21:47, Trond Myklebust wrote:
> > @@ -474,6 +482,18 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
> > }
> >
> > spin_lock(&inode_lock);
> > + /*
> > + * Special state for cleaning NFS unstable pages
> > + */
> > + if (inode->i_state & I_UNSTABLE_PAGES) {
> > + int err;
> > + inode->i_state &= ~I_UNSTABLE_PAGES;
> > + spin_unlock(&inode_lock);
> > + err = commit_unstable_pages(inode, wait);
> > + if (ret == 0)
> > + ret = err;
> > + spin_lock(&inode_lock);
> > + }
> I don't quite understand this chunk: We've called writeback_single_inode
> because it had some dirty pages. Thus it has I_DIRTY_DATASYNC set and a few
> lines above your chunk, we've called nfs_write_inode which sent commit to
> the server. Now here you sometimes send the commit again? What's the
> purpose?

We no longer set I_DIRTY_DATASYNC. We only set I_DIRTY_PAGES (and later
I_UNSTABLE_PAGES).

The point is that we now do the commit only _after_ we've sent all the
dirty pages, and waited for writeback to complete, whereas previously we
did it in the wrong order.

Cheers
Trond