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From: Brian Foster <bfoster@redhat.com>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
	linux-xfs@vger.kernel.org, david@fromorbit.com
Subject: Re: [PATCH 11/11] xfs: flush speculative space allocations when we run out of space
Date: Mon, 25 Jan 2021 16:06:28 -0500	[thread overview]
Message-ID: <20210125210628.GP2047559@bfoster> (raw)
In-Reply-To: <20210125200216.GE7698@magnolia>

On Mon, Jan 25, 2021 at 12:02:16PM -0800, Darrick J. Wong wrote:
> On Sun, Jan 24, 2021 at 09:48:16AM +0000, Christoph Hellwig wrote:
> > > +retry:
> > >  	/*
> > >  	 * Allocate the handle before we do our freeze accounting and setting up
> > >  	 * GFP_NOFS allocation context so that we avoid lockdep false positives
> > > @@ -285,6 +289,22 @@ xfs_trans_alloc(
> > >  	tp->t_firstblock = NULLFSBLOCK;
> > >  
> > >  	error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > +	if (error == -ENOSPC && tries > 0) {
> > > +		xfs_trans_cancel(tp);
> > > +
> > > +		/*
> > > +		 * We weren't able to reserve enough space for the transaction.
> > > +		 * Flush the other speculative space allocations to free space.
> > > +		 * Do not perform a synchronous scan because callers can hold
> > > +		 * other locks.
> > > +		 */
> > > +		error = xfs_blockgc_free_space(mp, NULL);
> > > +		if (error)
> > > +			return error;
> > > +
> > > +		tries--;
> > > +		goto retry;
> > > +	}
> > >  	if (error) {
> > >  		xfs_trans_cancel(tp);
> > >  		return error;
> > 
> > Why do we need to restart the whole function?  A failing
> > xfs_trans_reserve should restore tp to its initial state, and keeping
> > the SB_FREEZE_FS counter increased also doesn't look harmful as far as
> > I can tell.  So why not:
> > 
> > 	error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > 	if (error == -ENOSPC) {
> > 		/*
> > 		 * We weren't able to reserve enough space for the transaction.
> > 		 * Flush the other speculative space allocations to free space.
> > 		 * Do not perform a synchronous scan because callers can hold
> > 		 * other locks.
> > 		 */
> > 		error = xfs_blockgc_free_space(mp, NULL);
> 
> xfs_blockgc_free_space runs the blockgc scan directly, which means that
> it creates transactions to free blocks.  Since we can't have nested
> transactions, we have to drop tp here.
> 

Technically, I don't think it's a problem to hold a transaction memory
allocation (and superblock write access?) while diving into the scanning
mechanism. BTW, this also looks like a landmine passing a NULL eofb into
the xfs_blockgc_free_space() tracepoint.

Brian

> --D
> 
> > 		if (error)
> > 			return error;
> > 		error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > 	}
> >  	if (error) {
> >   		xfs_trans_cancel(tp);
> >   		return error;
> > 
> > ?
> 


  reply	other threads:[~2021-01-25 23:51 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-23 18:51 [PATCHSET v4 00/11] xfs: try harder to reclaim space when we run out Darrick J. Wong
2021-01-23 18:52 ` [PATCH 01/11] xfs: refactor messy xfs_inode_free_quota_* functions Darrick J. Wong
2021-01-25 18:13   ` Brian Foster
2021-01-25 19:33     ` Darrick J. Wong
2021-01-23 18:52 ` [PATCH 02/11] xfs: don't stall cowblocks scan if we can't take locks Darrick J. Wong
2021-01-25 18:14   ` Brian Foster
2021-01-25 19:54     ` Darrick J. Wong
2021-01-26 13:14       ` Brian Foster
2021-01-26 18:34         ` Darrick J. Wong
2021-01-26 20:03           ` Brian Foster
2021-01-27  3:09             ` Darrick J. Wong
2021-01-23 18:52 ` [PATCH 03/11] xfs: xfs_inode_free_quota_blocks should scan project quota Darrick J. Wong
2021-01-25 18:14   ` Brian Foster
2021-01-23 18:52 ` [PATCH 04/11] xfs: move and rename xfs_inode_free_quota_blocks to avoid conflicts Darrick J. Wong
2021-01-25 18:14   ` Brian Foster
2021-01-23 18:52 ` [PATCH 05/11] xfs: pass flags and return gc errors from xfs_blockgc_free_quota Darrick J. Wong
2021-01-24  9:34   ` Christoph Hellwig
2021-01-25 18:15   ` Brian Foster
2021-01-26  4:52   ` [PATCH v4.1 " Darrick J. Wong
2021-01-27 16:59     ` Christoph Hellwig
2021-01-27 17:11       ` Darrick J. Wong
2021-01-23 18:52 ` [PATCH 06/11] xfs: flush eof/cowblocks if we can't reserve quota for file blocks Darrick J. Wong
2021-01-24  9:39   ` Christoph Hellwig
2021-01-25 18:16     ` Brian Foster
2021-01-25 18:57       ` Darrick J. Wong
2021-01-26 13:26         ` Brian Foster
2021-01-26 21:12           ` Darrick J. Wong
2021-01-27 14:19             ` Brian Foster
2021-01-27 17:19               ` Darrick J. Wong
2021-01-26  4:53   ` [PATCH v4.1 " Darrick J. Wong
2021-01-23 18:52 ` [PATCH 07/11] xfs: flush eof/cowblocks if we can't reserve quota for inode creation Darrick J. Wong
2021-01-26  4:55   ` [PATCH v4.1 " Darrick J. Wong
2021-01-23 18:52 ` [PATCH 08/11] xfs: flush eof/cowblocks if we can't reserve quota for chown Darrick J. Wong
2021-01-26  4:55   ` [PATCH v4.1 " Darrick J. Wong
2021-01-23 18:52 ` [PATCH 09/11] xfs: add a tracepoint for blockgc scans Darrick J. Wong
2021-01-25 18:45   ` Brian Foster
2021-01-26  4:56   ` [PATCH v4.1 " Darrick J. Wong
2021-01-23 18:52 ` [PATCH 10/11] xfs: refactor xfs_icache_free_{eof,cow}blocks call sites Darrick J. Wong
2021-01-24  9:41   ` Christoph Hellwig
2021-01-25 18:46   ` Brian Foster
2021-01-26  2:33     ` Darrick J. Wong
2021-01-23 18:53 ` [PATCH 11/11] xfs: flush speculative space allocations when we run out of space Darrick J. Wong
2021-01-24  9:48   ` Christoph Hellwig
2021-01-25 18:46     ` Brian Foster
2021-01-25 20:02     ` Darrick J. Wong
2021-01-25 21:06       ` Brian Foster [this message]
2021-01-26  0:29         ` Darrick J. Wong
2021-01-27 16:57           ` Christoph Hellwig
2021-01-27 21:00             ` Darrick J. Wong
2021-01-26  4:59   ` [PATCH v4.1 " Darrick J. Wong
  -- strict thread matches above, loose matches on Subject: below --
2021-01-28  6:02 [PATCHSET v5 00/11] xfs: try harder to reclaim space when we run out Darrick J. Wong
2021-01-28  6:03 ` [PATCH 11/11] xfs: flush speculative space allocations when we run out of space Darrick J. Wong
2021-01-28  9:26   ` Christoph Hellwig
2021-01-18 22:11 [PATCHSET v3 00/11] xfs: try harder to reclaim space when we run out Darrick J. Wong
2021-01-18 22:12 ` [PATCH 11/11] xfs: flush speculative space allocations when we run out of space Darrick J. Wong

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