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From: David Wysochanski <dwysocha@redhat.com>
To: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trondmy@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>,
	linux-nfs <linux-nfs@vger.kernel.org>,
	v9fs-developer@lists.sourceforge.net,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	linux-cachefs <linux-cachefs@redhat.com>,
	linux-cifs <linux-cifs@vger.kernel.org>,
	Shyam Prasad N <nspmangalore@gmail.com>,
	Jeff Layton <jlayton@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 0/8] fscache: Replace and remove old I/O API
Date: Tue, 14 Sep 2021 11:30:29 -0400	[thread overview]
Message-ID: <CALF+zO=VHPzcp0A0KxpYW-0WnyxvM5gW5HmorzrMJ_arxxBchA@mail.gmail.com> (raw)
In-Reply-To: <163162767601.438332.9017034724960075707.stgit@warthog.procyon.org.uk>

On Tue, Sep 14, 2021 at 9:55 AM David Howells <dhowells@redhat.com> wrote:
>
>
> Here's a set of patches that removes the old fscache I/O API by the following
> means:
>
>  (1) A simple fallback API is added that can read or write a single page
>      synchronously.  The functions for this have "deprecated" in their names
>      as they have to be removed at some point.
>
>  (2) An implementation of this is provided in cachefiles.  It creates a kiocb
>      to use DIO to the backing file rather than calling readpage on the
>      backing filesystem page and then snooping the page wait queue.
>
>  (3) NFS is switched to use the fallback API.
>
>  (4) CIFS is switched to use the fallback API also for the moment.
>
>  (5) 9P is switched to using netfslib.
>
>  (6) The old I/O API is removed from fscache and the page snooping
>      implementation is removed from cachefiles.
>
> The reasons for doing this are:
>
>  (A) Using a kiocb to do asynchronous DIO from/to the pages of the backing
>      file is now a possibility that didn't exist when cachefiles was created.
>      This is much simpler than the snooping mechanism with a proper callback
>      path and it also requires fewer copies and less memory.
>
>  (B) We have to stop using bmap() or SEEK_DATA/SEEK_HOLE to work out what
>      blocks are present in the backing file is dangerous and can lead to data
>      corruption if the backing filesystem can insert or remove blocks of zeros
>      arbitrarily in order to optimise its extent list[1].
>
>      Whilst this patchset doesn't fix that yet, it does simplify the code and
>      the fix for that can be made in a subsequent patchset.
>
>  (C) In order to fix (B), the cache will need to keep track itself of what
>      data is present.  To make this easier to manage, the intention is to
>      increase the cache block granularity to, say, 256KiB - importantly, a
>      size that will span multiple pages - which means the single-page
>      interface will have to go away.  netfslib is designed to deal with
>      that on behalf of a filesystem, though a filesystem could use raw
>      cache calls instead and manage things itself.
>
> These patches can be found also on:
>
>         https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-iter-3
>
> David
>
> Link: https://lore.kernel.org/r/YO17ZNOcq+9PajfQ@mit.edu [1]
> ---
> David Howells (8):
>       fscache: Generalise the ->begin_read_operation method
>       fscache: Implement an alternate I/O interface to replace the old API
>       nfs: Move to using the alternate (deprecated) fscache I/O API
>       9p: (untested) Convert to using the netfs helper lib to do reads and caching
>       cifs: (untested) Move to using the alternate (deprecated) fscache I/O API
>       fscache: Remove the old I/O API
>       fscache: Remove stats that are no longer used
>       fscache: Update the documentation to reflect I/O API changes
>
>
>  .../filesystems/caching/backend-api.rst       |  138 +--
>  .../filesystems/caching/netfs-api.rst         |  386 +-----
>  fs/9p/Kconfig                                 |    1 +
>  fs/9p/cache.c                                 |  137 ---
>  fs/9p/cache.h                                 |   98 +-
>  fs/9p/v9fs.h                                  |    9 +
>  fs/9p/vfs_addr.c                              |  174 ++-
>  fs/9p/vfs_file.c                              |   21 +-
>  fs/cachefiles/Makefile                        |    1 -
>  fs/cachefiles/interface.c                     |   15 -
>  fs/cachefiles/internal.h                      |   38 -
>  fs/cachefiles/io.c                            |   28 +-
>  fs/cachefiles/main.c                          |    1 -
>  fs/cachefiles/rdwr.c                          |  972 ---------------
>  fs/cifs/file.c                                |   64 +-
>  fs/cifs/fscache.c                             |  105 +-
>  fs/cifs/fscache.h                             |   74 +-
>  fs/fscache/cache.c                            |    6 -
>  fs/fscache/cookie.c                           |   10 -
>  fs/fscache/internal.h                         |   58 +-
>  fs/fscache/io.c                               |  140 ++-
>  fs/fscache/object.c                           |    2 -
>  fs/fscache/page.c                             | 1066 -----------------
>  fs/fscache/stats.c                            |   73 +-
>  fs/nfs/file.c                                 |   14 +-
>  fs/nfs/fscache-index.c                        |   26 -
>  fs/nfs/fscache.c                              |  161 +--
>  fs/nfs/fscache.h                              |   84 +-
>  fs/nfs/read.c                                 |   25 +-
>  fs/nfs/write.c                                |    7 +-
>  include/linux/fscache-cache.h                 |  131 --
>  include/linux/fscache.h                       |  418 ++-----
>  include/linux/netfs.h                         |   17 +-
>  33 files changed, 508 insertions(+), 3992 deletions(-)
>  delete mode 100644 fs/cachefiles/rdwr.c
>
>

I tested an earlier version of these with NFS, which identified a
couple issues which you fixed.  Last I checked my unit tests and
xfstests were looking good. I'll do some testing on this latest branch
/ patches and report back.


  parent reply	other threads:[~2021-09-14 15:31 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14 13:54 [RFC PATCH 0/8] fscache: Replace and remove old I/O API David Howells
2021-09-14 13:54 ` [PATCH 1/8] fscache: Generalise the ->begin_read_operation method David Howells
2021-09-14 13:55 ` [PATCH 2/8] fscache: Implement an alternate I/O interface to replace the old API David Howells
2021-09-14 13:55 ` [PATCH 3/8] nfs: Move to using the alternate (deprecated) fscache I/O API David Howells
2021-09-14 13:55 ` [PATCH 4/8] 9p: (untested) Convert to using the netfs helper lib to do reads and caching David Howells
2021-09-14 14:02   ` Jeff Layton
2021-09-14 14:09   ` David Howells
2021-09-14 21:51     ` Dominique Martinet
2021-09-14 21:59     ` David Howells
2021-09-21 11:15   ` Dominique Martinet
2021-09-14 13:55 ` [PATCH 5/8] cifs: (untested) Move to using the alternate (deprecated) fscache I/O API David Howells
2021-09-14 13:55 ` [PATCH 6/8] fscache: Remove the old " David Howells
2021-09-14 13:56 ` [PATCH 7/8] fscache: Remove stats that are no longer used David Howells
2021-09-14 13:56 ` [PATCH 8/8] fscache: Update the documentation to reflect I/O API changes David Howells
2021-09-14 15:30 ` David Wysochanski [this message]
2021-09-20 12:54   ` [RFC PATCH 0/8] fscache: Replace and remove old I/O API David Wysochanski
2021-09-14 15:49 ` Jeff Layton
2021-09-14 16:21 ` Linus Torvalds
2021-09-14 16:24   ` Linus Torvalds
2021-09-14 18:59   ` David Howells

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