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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Gao Xiang <hsiangkao@redhat.com>
Cc: linux-xfs@vger.kernel.org, Dave Chinner <david@fromorbit.com>,
	Brian Foster <bfoster@redhat.com>
Subject: Re: [RFC PATCH v4 0/3] xfs: more unlinked inode list optimization v4
Date: Tue, 18 Aug 2020 17:53:34 -0700
Message-ID: <20200819005334.GA6096@magnolia> (raw)
In-Reply-To: <20200818133015.25398-1-hsiangkao@redhat.com>

On Tue, Aug 18, 2020 at 09:30:12PM +0800, Gao Xiang wrote:
> Hi forks,
> 
> This is RFC v4 version which is based on Dave's latest patchset:
>  https://lore.kernel.org/r/20200812092556.2567285-1-david@fromorbit.com

As we already discussed on IRC, please send new revisions of patchsets
as a separate thread from the old submission.

> I didn't send out v3 because it was based on Dave's previous RFC
> patchset, but I'm still not quite sure to drop RFC tag since this
> version is different from the previous versions...

Hm, this cover letter could use some tidying up, since it took me a bit
of digging to figure out that yes, this is the successor of the old
series that tried to get the AGI buffer lock out of the way if we're
adding a newly unlinked inode to the end of the unlinked list.

> Changes since v2:
>  - rebase on new patchset, and omit the original first patch
>    "xfs: arrange all unlinked inodes into one list" since it now
>    has better form in the base patchset;
> 
>  - a tail xfs_inode pointer is no longer needed since the original
>    patchset introduced list_head iunlink infrastructure and it can
>    be used to get the tail inode;
> 
>  - take pag_iunlink_mutex lock until all iunlink log items are
>    committed. Otherwise, xfs_iunlink_log() order would not be equal
>    to the trans commit order so it can mis-reorder and cause metadata
>    corruption I mentioned in v2.
> 
>    In order to archive that, some recursive count is introduced since
>    there could be several iunlink operations in one transaction,
>    and introduce some per-AG fields as well since these operations
>    in the transaction may not operate inodes in the same AG. we may
>    also need to take AGI buffer lock in advance (e.g. whiteout rename
>    path) due to iunlink operations and locking order constraint.
>    For more details, see related inlined comments as well...
> 
>  - "xfs: get rid of unused pagi_unlinked_hash" would be better folded
>    into original patchset since pagi_unlinked_hash is no longer needed.
> 
> ============
> 
> [Original text]
> 
> This RFC patchset mainly addresses the thoughts [*] and [**] from Dave's
> original patchset,
> https://lore.kernel.org/r/20200623095015.1934171-1-david@fromorbit.com
> 
> In short, it focues on the following ideas mentioned by Dave:
>  - use bucket 0 instead of multiple buckets since in-memory double
>    linked list finally works;
> 
>  - avoid taking AGI buffer and unnecessary AGI update if possible, so
>    1) add a new lock and keep proper locking order to avoid deadlock;
>    2) insert a new unlinked inode from the tail instead of head;
> 
> In addition, it's worth noticing 3 things:
>  - xfs_iunlink_remove() should support old multiple buckets in order
>    to keep old inode unlinked list (old image) working when recovering.
> 
>  - (but) OTOH, the old kernel recovery _shouldn't_ work with new image
>    since the bucket_index from old xfs_iunlink_remove() is generated
>    by the old formula (rather than keep in xfs_inode), which is now
>    fixed as 0. So this feature is not forward compatible without some
>    extra backport patches;

Oh?  These seem like serious limitations, are they still true?

--D

>  - a tail xfs_inode pointer is also added in the perag, which keeps 
>    track of the tail of bucket 0 since it's mainly used for xfs_iunlink().
> 
> 
> The git tree is also available at
> git://git.kernel.org/pub/scm/linux/kernel/git/xiang/linux.git tags/xfs/iunlink_opt_v4
> 
> Gitweb:
> https://git.kernel.org/pub/scm/linux/kernel/git/xiang/linux.git/log/?h=xfs/iunlink_opt_v4
> 
> 
> Some preliminary tests are done (including fstests, but there seems
> some pre-exist failures and I haven't looked into yet). And I confirmed
> there was no previous metadata corruption mentioned in RFC v2 anymore.
> 
> To confirm that I'm in the right direction, I post the latest version
> now since it haven't been updated for a while.
> 
> Comments and directions are welcomed. :)
> 
> Thanks,
> Gao Xiang
> 
> Gao Xiang (3):
>   xfs: get rid of unused pagi_unlinked_hash
>   xfs: introduce perag iunlink lock
>   xfs: insert unlinked inodes from tail
> 
>  fs/xfs/xfs_inode.c        | 194 ++++++++++++++++++++++++++++++++------
>  fs/xfs/xfs_inode.h        |   1 +
>  fs/xfs/xfs_iunlink_item.c |  16 ++++
>  fs/xfs/xfs_mount.c        |   4 +
>  fs/xfs/xfs_mount.h        |  14 +--
>  5 files changed, 193 insertions(+), 36 deletions(-)
> 
> -- 
> 2.18.1
> 

  parent 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
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     ` Darrick J. Wong [this message]
2020-08-19  1:14       ` [RFC PATCH v4 0/3] xfs: more unlinked inode list optimization v4 Gao Xiang
2020-08-20  2:46     ` Darrick J. Wong
2020-08-20  4:01       ` Gao Xiang

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