linux-ext4 - Re: [PATCH] ext4: Fix delalloc sync hang with journal lock inversion

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Message-ID: <20080602095956.GB9225@skywalker>
Date:	Mon, 2 Jun 2008 15:29:56 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Jan Kara <jack@...e.cz>
Cc:	cmm@...ibm.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix delalloc sync hang with journal lock
	inversion

On Mon, Jun 02, 2008 at 11:35:00AM +0200, Jan Kara wrote:
> > @@ -1052,6 +1051,7 @@ static int __mpage_da_writepage(struct page *page,
> >  		head = page_buffers(page);
> >  		bh = head;
> >  		do {
> > +
>   I guess this line is a typo.
> 

Yes, Mostly some debug lines I removed, but missed the newline added.


> >  			BUG_ON(buffer_locked(bh));
> >  			if (buffer_dirty(bh))
> >  				mpage_add_bh_to_extent(mpd, logical, bh);
> > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > index 789b6ad..655b8bf 100644
> > --- a/mm/page-writeback.c
> > +++ b/mm/page-writeback.c
> > @@ -881,7 +881,12 @@ int write_cache_pages(struct address_space *mapping,
> >  	pagevec_init(&pvec, 0);
> >  	if (wbc->range_cyclic) {
> >  		index = mapping->writeback_index; /* Start from prev offset */
> > -		end = -1;
> > +		/*
> > +		 * write only till the specified range_end even in cyclic mode
> > +		 */
> > +		end = wbc->range_end >> PAGE_CACHE_SHIFT;
> > +		if (!end)
> > +			end = -1;
> >  	} else {
> >  		index = wbc->range_start >> PAGE_CACHE_SHIFT;
> >  		end = wbc->range_end >> PAGE_CACHE_SHIFT;
>   Are you sure you won't break other users of range_cyclic with this
> change?
>

I haven't run any specific test to verify that. The concern was that if
we force cyclic mode for writeout in delalloc we may be starting the
writeout from a different offset than specified and would be writing
more. So the changes was to use the offset specified. A quick look at
the kernel suggested most of them had range_end as 0 with cyclic_mode.
I haven't audited the full kernel. I will do that. Meanwhile if you
think it is risky to make this changes i guess we should drop this
part. But i guess we can keep the below change

+       index =  mapping->writeback_index;
+       if (!range_cyclic) {
+               /*
+                * We force cyclic write out of pages. If the
+                * caller didn't request for range_cyclic update
+                * set the writeback_index to what the caller requested.
+                */
+               mapping->writeback_index = wbc->range_start >> PAGE_CACHE_SHIFT;
+       }


-aneesh
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