lkml.org 
[lkml]   [2011]   [May]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 02/17] writeback: update dirtied_when for synced inode to prevent livelock
> > > @@ -419,6 +419,15 @@ writeback_single_inode(struct inode *ino
> > > spin_lock(&inode->i_lock);
> > > inode->i_state &= ~I_SYNC;
> > > if (!(inode->i_state & I_FREEING)) {
> > > + /*
> > > + * Sync livelock prevention. Each inode is tagged and synced in
> > > + * one shot, so we can unconditionally update its dirty time to
> > > + * prevent syncing it again. Note that time ordering of b_dirty
> > > + * list will be kept because the following code either removes
> > > + * the inode from b_dirty or calls redirty_tail().
> > > + */
> > > + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
> > > + inode->dirtied_when = jiffies;
> >
> > Shouldn't this update only ocur if the inode is still dirty?
>
> Yeah, that would be better even though the current form won't lead to
> errors.
>
> Let's add one more test (inode->i_state & I_DIRTY)?
> (I was actually aware of the trade offs and didn't bother to add it..)

Oops, the (inode->i_state & I_DIRTY) test is not enough because
when the inode is actively dirtied, I_DIRTY_PAGES won't be set when
the flusher is writing out the pages with I_SYNC set...

Well it would look clumsy to add another mapping_tagged(mapping,
PAGECACHE_TAG_DIRTY) test. So I tend to revert to the original scheme
of updating ->dirtied_when only on newly dirtied pages. It's the
simplest form that can avoid unnecessarily polluting ->dirtied_when.

@@ -432,6 +432,15 @@ writeback_single_inode(struct inode *ino
requeue_io(inode);
} else {
/*
+ * Sync livelock prevention. Each inode is
+ * tagged and synced in one shot, so we can
+ * unconditionally update its dirty time to
+ * prevent syncing it again.
+ */
+ if (wbc->sync_mode == WB_SYNC_ALL ||
+ wbc->tagged_writepages)
+ inode->dirtied_when = jiffies;
+ /*
* Writeback blocked by something other than
* congestion. Delay the inode for some time to
* avoid spinning on the CPU (100% iowait)

Thanks,
Fengguang


\
 
 \ /
  Last update: 2011-05-19 23:33    [W:0.080 / U:0.364 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site