From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Wengang Wang <wen.gang.wang@oracle.com>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 0/9] xfs file non-exclusive online defragment
Date: Thu, 14 Dec 2023 20:06:41 -0800 [thread overview]
Message-ID: <ZXvQ0YDfHBuvLXbY@infradead.org> (raw)
In-Reply-To: <20231214213502.GI361584@frogsfrogsfrogs>
On Thu, Dec 14, 2023 at 01:35:02PM -0800, Darrick J. Wong wrote:
> I'm kinda surprised you don't just turn on alwayscow mode, use an
> iomap_funshare-like function to read in and dirty pagecache (which will
> hopefully create a new large cow fork mapping) and then flush it all
> back out with writeback. Then you don't need all this state tracking,
> kthreads management, and copying file data through the buffer cache.
> Wouldn't that be a lot simpler?
Yes, although with a caveat or two.
We did that for the zoned XFS project, where a 'defragmentation' like
this which we call garbage collection is an essential part of the
operation to free entire zones. I ended up initially implementing it
using iomap_file_unshare as that is page cache coherent and a nicely
available library function. But it turns out iomap_file_unshare sucks
badly as it will read the data sychronously one block at a time.
I ended up coming up with my own duplication of iomap_file_unshare
that doesn't do it which is a bit hack by solves this problem.
I'd love to eventually merge it back into iomap_file_unshare, for
which we really need to work on our writeback iterators.
The relevant commit or the new helper is here:
http://git.infradead.org/users/hch/xfs.git/commitdiff/cc4a639e3052fefb385f63a0db5dfe07db4e9d58
which also need a hacky readahead helper:
http://git.infradead.org/users/hch/xfs.git/commitdiff/f6d545fc00300ddfd3e297d17e4f229ad2f15c3e
The code using this for zoned GC is here:
http://git.infradead.org/users/hch/xfs.git/blob/refs/heads/xfs-zoned:/fs/xfs/xfs_zone_alloc.c#l764
It probably would make sense to be able to also use this for a regular
fs for the online defrag use case, although the wire up would be a bit
different.
next prev parent reply other threads:[~2023-12-15 4:06 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-14 17:05 [PATCH 0/9] xfs file non-exclusive online defragment Wengang Wang
2023-12-14 17:05 ` [PATCH 1/9] xfs: defrag: introduce strucutures and numbers Wengang Wang
2023-12-15 5:35 ` kernel test robot
2023-12-14 17:05 ` [PATCH 2/9] xfs: defrag: initialization and cleanup Wengang Wang
2023-12-15 14:09 ` kernel test robot
2023-12-14 17:05 ` [PATCH 3/9] xfs: defrag implement stop/suspend/resume/status Wengang Wang
2023-12-14 17:05 ` [PATCH 4/9] xfs: defrag: allocate/cleanup defragmentation Wengang Wang
2023-12-14 17:05 ` [PATCH 5/9] xfs: defrag: process some cases in xfs_defrag_process Wengang Wang
2023-12-14 17:05 ` [PATCH 6/9] xfs: defrag: piece picking up Wengang Wang
2023-12-14 17:05 ` [PATCH 7/9] xfs: defrag: guarantee contigurous blocks in cow fork Wengang Wang
2023-12-14 17:05 ` [PATCH 8/9] xfs: defrag: copy data from old blocks to new blocks Wengang Wang
2023-12-14 17:05 ` [PATCH 9/9] xfs: defrag: map " Wengang Wang
2023-12-14 21:35 ` [PATCH 0/9] xfs file non-exclusive online defragment Darrick J. Wong
2023-12-15 3:15 ` Dave Chinner
2023-12-15 17:07 ` Wengang Wang
2023-12-15 17:30 ` Darrick J. Wong
2023-12-15 20:03 ` Wengang Wang
2023-12-15 20:20 ` Dave Chinner
2023-12-18 16:27 ` Wengang Wang
2023-12-19 21:17 ` Wengang Wang
2023-12-19 21:29 ` Dave Chinner
2023-12-19 22:23 ` Wengang Wang
2023-12-15 4:06 ` Christoph Hellwig [this message]
2023-12-15 16:48 ` Wengang Wang
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