linux-kernel - Re: [vm] writing to UDF DVD+RW (/dev/sr0) while under memory pressure: box ==> doorstop

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Date:	Thu, 10 Jan 2008 18:16:43 +0100
From:	Jan Kara <jack@...e.cz>
To:	Mike Galbraith <efault@....de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	bfennema@...con.csc.calpoly.edu
Subject: Re: [vm] writing to UDF DVD+RW (/dev/sr0) while under memory
	pressure: box ==> doorstop

On Thu 10-01-08 16:29:50, Mike Galbraith wrote:
> 
> On Thu, 2008-01-10 at 15:41 +0100, Jan Kara wrote:
> > > On Wed, 09 Jan 2008 12:11:20 +0100
> > > 
> > > 
> > > I wonder why UDF was doing a synchronous write in there.  In fact I wonder
> > > why it's writing the inode at all?  extN doesn't do that.  If for some
> > > reason it really does want to make the inode immediately reclaimable then
> > > simply shoving it down into the /dev/hda1 pagecache should be sufficient
> > > (ie: what you did)..
> >   Looking at the code, I think UDF change is correct. UDF has to call
> > write_inode_now() because by the time clear_inode() is called, inode is
> > already written by VFS and prepared to be freed. But then UDF modifies
> > it in udf_clear_inode() (removes preallocation) and for these changes to
> > get to disk you have to write the inode explicitely. 
> >   But there's really no need to wait on IO. We only have to copy all
> > data from inode structure into buffers and that happens even if we don't
> > wait on sync.
> 
> Perhaps I should go ahead and submit it then.  There are 5 other async
> callers as well, so VM/UDF reclaim buglet can die, and those others can
> get what they asked for with net diffstat of 0.
> 
> Fix udf_clear_inode() to request asynchronous writeout in icache reclaim
> path, and ensure that write_inore_now() honors that request, lest
> allocators needlessly block on iprune_mutex.
> 
> Signed-off-by: Mike Galbraith <efault@....de>
  Acked-by: Jan Kara <jack@...e.cz>
  if it's worth anything ;)
									Honza

> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 0fca820..f1cce24 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -657,7 +657,7 @@ int write_inode_now(struct inode *inode, int sync)
>  	int ret;
>  	struct writeback_control wbc = {
>  		.nr_to_write = LONG_MAX,
> -		.sync_mode = WB_SYNC_ALL,
> +		.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
>  		.range_start = 0,
>  		.range_end = LLONG_MAX,
>  	};
> diff --git a/fs/udf/inode.c b/fs/udf/inode.c
> index 6ff8151..d1fc116 100644
> --- a/fs/udf/inode.c
> +++ b/fs/udf/inode.c
> @@ -117,7 +117,7 @@ void udf_clear_inode(struct inode *inode)
>  		udf_discard_prealloc(inode);
>  		udf_truncate_tail_extent(inode);
>  		unlock_kernel();
> -		write_inode_now(inode, 1);
> +		write_inode_now(inode, 0);
>  	}
>  	kfree(UDF_I_DATA(inode));
>  	UDF_I_DATA(inode) = NULL;
> 
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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