Messages in this thread | | | Date | Sun, 20 Sep 2009 10:35:28 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH] fs: Fix busyloop in wb_writeback() |
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On Thu, Sep 17, 2009 at 01:22:48AM +0800, Jan Kara wrote: > If all inodes are under writeback (e.g. in case when there's only one inode > with dirty pages), wb_writeback() with WB_SYNC_NONE work basically degrades > to busylooping until I_SYNC flags of the inode is cleared. Fix the problem by > waiting on I_SYNC flags of an inode on b_more_io list in case we failed to > write anything.
Sorry, I realized that inode_wait_for_writeback() waits for I_SYNC. But inodes in b_more_io are not expected to have I_SYNC set. So your patch looks like a big no-op?
The busy loop does exists, when bdi is congested. In this case, write_cache_pages() will refuse to write anything, we used to be calling congestion_wait() to take a breath, but now wb_writeback() purged that call and thus created a busy loop.
So the solution (at least for this merge window) should be to restore the congestion_wait() call.
Thanks, Fengguang
> CC: Wu Fengguang <fengguang.wu@intel.com> > Signed-off-by: Jan Kara <jack@suse.cz> > --- > fs/fs-writeback.c | 19 ++++++++++++++++++- > 1 files changed, 18 insertions(+), 1 deletions(-) > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > index 8e1e5e1..c59d673 100644 > --- a/fs/fs-writeback.c > +++ b/fs/fs-writeback.c > @@ -706,6 +706,7 @@ static long wb_writeback(struct bdi_writeback *wb, > }; > unsigned long oldest_jif; > long wrote = 0; > + struct inode *inode; > > if (wbc.for_kupdate) { > wbc.older_than_this = &oldest_jif; > @@ -747,8 +748,24 @@ static long wb_writeback(struct bdi_writeback *wb, > * If we ran out of stuff to write, bail unless more_io got set > */ > if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { > - if (wbc.more_io && !wbc.for_kupdate) > + if (wbc.more_io && !wbc.for_kupdate) { > + if (wbc.nr_to_write < MAX_WRITEBACK_PAGES) > + continue; > + /* > + * Nothing written. Wait for some inode to > + * become available for writeback. Otherwise > + * we'll just busyloop. > + */ > + spin_lock(&inode_lock); > + if (!list_empty(&wb->b_more_io)) { > + inode = list_entry( > + wb->b_more_io.prev, > + struct inode, i_list); > + inode_wait_for_writeback(inode); > + } > + spin_unlock(&inode_lock); > continue; > + } > break; > } > } > -- > 1.6.0.2
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