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From: Gao Xiang <hsiangkao@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Brian Foster <bfoster@redhat.com>
Subject: Re: [RFC PATCH 2/2] xfs: don't access AGI on unlinked inodes if it can
Date: Thu, 9 Jul 2020 18:36:21 +0800
Message-ID: <20200709103621.GD15249@xiangao.remote.csb> (raw)
In-Reply-To: <20200709023246.GR2005@dread.disaster.area>

Hi Dave,

On Thu, Jul 09, 2020 at 12:32:46PM +1000, Dave Chinner wrote:

...

> > > 	if (trylock AGI)
> > > 		return;
> > 
> > (adding some notes here, this patch doesn't use try lock here
> >  finally but unlock perag and take AGI and relock and recheck tail_empty....
> >  since the tail non-empty is rare...)
> 
> *nod*
> 
> My point was largely that this sort of thing is really obvious and
> easy to optimise once the locking is cleanly separated. Adding a
> trylock rather than drop/relock is another patch for the series :P

I thought trylock way yesterday as well...
Apart from that we don't have the AGI trylock method yet, it seems
not work as well...

Thinking about one thread is holding a AGI lock and wants to lock perag.
And another thread holds a perag, but the trylock will fail and the second
wait-lock will cause deadlock... like below:

Thread 1			Thread 2
 lock AGI
                                 lock perag
 lock perag
                                 trylock AGI
                                 lock AGI           <- dead lock here

And trylock perag instead seems not work well as well, since it fails
more frequently so we need lock AGI and then lock perag as a fallback.

So currently, I think it's better to use unlock, do something, regrab,
recheck method for now...

And yeah, that can be done in another patch if some better way. (e.g.
moving modifing AGI into pre-commit, so we can only take one per-ag
lock here...)

Thanks,
Gao Xiang

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> 


  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-07 13:57 [RFC PATCH 0/2] xfs: more unlinked inode list optimization v1 Gao Xiang
2020-07-07 13:57 ` [RFC PATCH 1/2] xfs: arrange all unlinked inodes into one list Gao Xiang
2020-07-08 22:33   ` Dave Chinner
2020-07-09  0:17     ` Gao Xiang
2020-07-07 13:57 ` [RFC PATCH 2/2] xfs: don't access AGI on unlinked inodes if it can Gao Xiang
2020-07-08 17:03   ` Darrick J. Wong
2020-07-08 23:40     ` Gao Xiang
2020-07-08 23:33   ` Dave Chinner
2020-07-09  0:55     ` Gao Xiang
2020-07-09  2:32       ` Dave Chinner
2020-07-09 10:36         ` Gao Xiang [this message]
2020-07-09 10:47           ` Gao Xiang
2020-07-09 22:36           ` Dave Chinner
2020-07-24  6:12 ` [RFC PATCH v2 0/3] xfs: more unlinked inode list optimization v2 Gao Xiang
2020-07-24  6:12   ` [RFC PATCH v2 1/3] xfs: arrange all unlinked inodes into one list Gao Xiang
2020-07-24  6:12   ` [RFC PATCH v2 2/3] xfs: introduce perag iunlink lock Gao Xiang
2020-07-24  6:12   ` [RFC PATCH v2 3/3] xfs: insert unlinked inodes from tail Gao Xiang
2020-08-18 13:30   ` [RFC PATCH v4 0/3] xfs: more unlinked inode list optimization v4 Gao Xiang
2020-08-18 13:30     ` [RFC PATCH v4 1/3] xfs: get rid of unused pagi_unlinked_hash Gao Xiang
2020-08-19  0:54       ` Darrick J. Wong
2020-08-21  1:09         ` Dave Chinner
2020-08-18 13:30     ` [RFC PATCH v4 2/3] xfs: introduce perag iunlink lock Gao Xiang
2020-08-19  1:06       ` Darrick J. Wong
2020-08-19  1:23         ` Gao Xiang
2020-08-18 13:30     ` [RFC PATCH v4 3/3] xfs: insert unlinked inodes from tail Gao Xiang
2020-08-19  0:53     ` [RFC PATCH v4 0/3] xfs: more unlinked inode list optimization v4 Darrick J. Wong
2020-08-19  1:14       ` Gao Xiang
2020-08-20  2:46     ` Darrick J. Wong
2020-08-20  4:01       ` Gao Xiang

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