Re: [patch 1/1] Writeback fix for concurrent large and small file writes

[Michael Rubin]

So Feng's one line change fixes the problem at hand. I will do some
more testing with it and then submit his patch credited with him for
2.6.24. If that's cool with Feng.

Also I will take the comment changes and re-submit my patch for 2.6.25
for general purpose improvement and see what happens.

mrubin

On Nov 28, 2007 4:34 PM, Fengguang Wu <wfg@xxxxxxxxxxxxxxxx> wrote:
> On Wed, Nov 28, 2007 at 11:29:57AM -0800, Michael Rubin wrote:
> > >From mrubin@xxxxxxxxxxxxxxxxxxxxxxxxxx Wed Nov 28 11:10:06 2007
> > Message-Id: <20071128190121.716364000@xxxxxxxxxxxxxxxxxxxxxxxxxx>
> > Date: Wed, 28 Nov 2007 11:01:21 -0800
> > From: mrubin@xxxxxxxxxx
> > To: mrubin@xxxxxxxxxx
> > Subject: [patch 1/1] Writeback fix for concurrent large and small file writes.
> >
> > From: Michael Rubin <mrubin@xxxxxxxxxx>
> >
> > Fixing a bug where writing to large files while concurrently writing to
> > smaller ones creates a situation where writeback cannot keep up with the
>
> Could you demonstrate the situation? Or if I guess it right, could it
> be fixed by the following patch? (not a nack: If so, your patch could
> also be considered as a general purpose improvement, instead of a bug
> fix.)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 0fca820..62e62e2 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -301,7 +301,7 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
>                          * Someone redirtied the inode while were writing back
>                          * the pages.
>                          */
> -                       redirty_tail(inode);
> +                       requeue_io(inode);
>                 } else if (atomic_read(&inode->i_count)) {
>                         /*
>                          * The inode is clean, inuse
>
> Thank you,
> Fengguang
>
>
> > traffic and memory baloons until the we hit the threshold watermark. This
> > can result in surprising latency spikes when syncing. This latency
> > can take minutes on large memory systems. Upon request I can provide
> > a test to reproduce this situation. The flush tree fixes this issue and
> > fixes several other minor issues with fairness also.
> >
> > 1) Adding a data structure to guarantee fairness when writing inodes
> > to disk.  The flush_tree is based on an rbtree. The only difference is
> > how duplicate keys are chained off the same rb_node.
> >
> > 2) Added a FS flag to mark file systems that are not disk backed so we
> > don't have to flush them. Not sure I marked all of them. But just marking
> > these improves writeback performance.
> >
> > 3) Added an inode flag to allow inodes to be marked so that they are
> > never written back to disk. See get_pipe_inode.
> >
> > Under autotest this patch has passed: fsx, bonnie, and iozone. I am
> > currently writing more writeback focused tests (which so far have been
> > passed) to add into autotest.
> >
> > Signed-off-by: Michael Rubin <mrubin@xxxxxxxxxx>
> > ---
>
>
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