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    SubjectRe: [fuse-devel] [PATCH v4 00/14] fuse: An attempt to implement a write-back cache policy
    Hi Miklos,

    Any feedback would be highly appreciated.

    Thanks,
    Maxim

    04/01/2013 02:40 PM, Maxim V. Patlasov пишет:
    > Hi,
    >
    > This is the fourth iteration of Pavel Emelyanov's patch-set implementing
    > write-back policy for FUSE page cache. Initial patch-set description was
    > the following:
    >
    > One of the problems with the existing FUSE implementation is that it uses the
    > write-through cache policy which results in performance problems on certain
    > workloads. E.g. when copying a big file into a FUSE file the cp pushes every
    > 128k to the userspace synchronously. This becomes a problem when the userspace
    > back-end uses networking for storing the data.
    >
    > A good solution of this is switching the FUSE page cache into a write-back policy.
    > With this file data are pushed to the userspace with big chunks (depending on the
    > dirty memory limits, but this is much more than 128k) which lets the FUSE daemons
    > handle the size updates in a more efficient manner.
    >
    > The writeback feature is per-connection and is explicitly configurable at the
    > init stage (is it worth making it CAP_SOMETHING protected?) When the writeback is
    > turned ON:
    >
    > * still copy writeback pages to temporary buffer when sending a writeback request
    > and finish the page writeback immediately
    >
    > * make kernel maintain the inode's i_size to avoid frequent i_size synchronization
    > with the user space
    >
    > * take NR_WRITEBACK_TEMP into account when makeing balance_dirty_pages decision.
    > This protects us from having too many dirty pages on FUSE
    >
    > The provided patchset survives the fsx test. Performance measurements are not yet
    > all finished, but the mentioned copying of a huge file becomes noticeably faster
    > even on machines with few RAM and doesn't make the system stuck (the dirty pages
    > balancer does its work OK). Applies on top of v3.5-rc4.
    >
    > We are currently exploring this with our own distributed storage implementation
    > which is heavily oriented on storing big blobs of data with extremely rare meta-data
    > updates (virtual machines' and containers' disk images). With the existing cache
    > policy a typical usage scenario -- copying a big VM disk into a cloud -- takes way
    > too much time to proceed, much longer than if it was simply scp-ed over the same
    > network. The write-back policy (as I mentioned) noticeably improves this scenario.
    > Kirill (in Cc) can share more details about the performance and the storage concepts
    > details if required.
    >
    > Changed in v2:
    > - numerous bugfixes:
    > - fuse_write_begin and fuse_writepages_fill and fuse_writepage_locked must wait
    > on page writeback because page writeback can extend beyond the lifetime of
    > the page-cache page
    > - fuse_send_writepages can end_page_writeback on original page only after adding
    > request to fi->writepages list; otherwise another writeback may happen inside
    > the gap between end_page_writeback and adding to the list
    > - fuse_direct_io must wait on page writeback; otherwise data corruption is possible
    > due to reordering requests
    > - fuse_flush must flush dirty memory and wait for all writeback on given inode
    > before sending FUSE_FLUSH to userspace; otherwise FUSE_FLUSH is not reliable
    > - fuse_file_fallocate must hold i_mutex around FUSE_FALLOCATE and i_size update;
    > otherwise a race with a writer extending i_size is possible
    > - fix handling errors in fuse_writepages and fuse_send_writepages
    > - handle i_mtime intelligently if writeback cache is on (see patch #7 (update i_mtime
    > on buffered writes) for details.
    > - put enabling writeback cache under fusermount control; (see mount option
    > 'allow_wbcache' introduced by patch #13 (turn writeback cache on))
    > - rebased on v3.7-rc5
    >
    > Changed in v3:
    > - rebased on for-next branch of the fuse tree (fb05f41f5f96f7423c53da4d87913fb44fd0565d)
    >
    > Changed in v4:
    > - rebased on for-next branch of the fuse tree (634734b63ac39e137a1c623ba74f3e062b6577db)
    > - fixed fuse_fillattr() for non-writeback_chace case
    > - added comments explaining why we cannot trust size from server
    > - rewrote patch handling i_mtime; it's titled Trust-kernel-i_mtime-only now
    > - simplified patch titled Flush-files-on-wb-close
    > - eliminated code duplications from fuse_readpage() ans fuse_prepare_write()
    > - added comment about "disk full" errors to fuse_write_begin()
    >
    > Thanks,
    > Maxim
    >
    > ---
    >
    > Maxim V. Patlasov (14):
    > fuse: Linking file to inode helper
    > fuse: Getting file for writeback helper
    > fuse: Prepare to handle short reads
    > fuse: Prepare to handle multiple pages in writeback
    > fuse: Connection bit for enabling writeback
    > fuse: Trust kernel i_size only - v3
    > fuse: Trust kernel i_mtime only
    > fuse: Flush files on wb close
    > fuse: Implement writepages and write_begin/write_end callbacks - v3
    > fuse: fuse_writepage_locked() should wait on writeback
    > fuse: fuse_flush() should wait on writeback
    > fuse: Fix O_DIRECT operations vs cached writeback misorder - v2
    > fuse: Turn writeback cache on
    > mm: Account for WRITEBACK_TEMP in balance_dirty_pages
    >
    >
    > fs/fuse/cuse.c | 5
    > fs/fuse/dir.c | 127 +++++++++-
    > fs/fuse/file.c | 575 ++++++++++++++++++++++++++++++++++++++++-----
    > fs/fuse/fuse_i.h | 26 ++
    > fs/fuse/inode.c | 37 +++
    > include/uapi/linux/fuse.h | 2
    > mm/page-writeback.c | 3
    > 7 files changed, 689 insertions(+), 86 deletions(-)
    >

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