On 2021/7/26 下午6:08, Neal Gompa wrote:

On Mon, Jul 26, 2021 at 2:36 AM Qu Wenruo [off-list ref] wrote:

quoted

This much smaller patchset can be fetched from github:
https://github.com/adam900710/linux/tree/subpage

These patchset is targeted at v5.15 merge window.
There are 11 subpage enablment patches pending for a while, and not
touched, thus they should be pretty stable and safe.

While there are 7 new patches, 4 of them are straightforward small
fixes, the remaining 2 are a little scary as they reworked the core code
of compression.
The final new patch is a special write path hotfix, aiming to make btrfs
subpage writeback more robust against tests like dm-dust.

The rework should improve the readabilty thus make reviewing a
little easier (as least I hope so).

=== Current stage ===
The tests on x86 pass without new failure, and generic test group on
arm64 with 64K page size passes except known failure and defrag group.

For btrfs test group, all pass except compression/raid56/defrag.

For anyone who is interested in testing, please use btrfs-progs v5.12 to
avoid false alert at mkfs time.

=== Limitation ===
There are several limitations introduced just for subpage:
- No compressed write support
   Read is no problem, but compression write path has more things left to
   be modified.

   Already have a version passing all test groups with "-o compress"
   mount option.
   Will be addressed in later patchset.

If you already have this working, why not include it in the patch series?

This patchset is for v5.15 merge window, while the compression is only 
targeted no later than v5.16.

Furthermore, that patchset is pretty big, 28 patches.

Combining them together would create a 46 patches set, no one will be 
happy to do any review on that.

Thanks,
Qu

quoted

- No inline extent will be created
   This is mostly due to the fact that filemap_fdatawrite_range() will
   trigger more write than the range specified.
   In fallocate calls, this behavior can make us to writeback which can
   be inlined, before we enlarge the isize, causing inline extent being
   created along with regular extents.

   In fact, even on x86_64, we can still have fsstress to create inodes
   with mixed inline and regular extents.
   Thus there is a much bigger problem to solve.

- No support for RAID56
   There are still too many hardcoded PAGE_SIZE in raid56 code.
   Considering it's already considered unsafe due to its write-hole
   problem, disabling RAID56 for subpage looks sane to me.

- No defrag support for subpage
   The support for subpage defrag has already an initial version
   submitted to the mail list.
   Thus the correct support won't be included in this patchset.

   Currently I'm not pushing defrag patchset, as it's really not
   the priority, and still has rare bugs related to EXTENT_DELALLOC_NEW
   extent bit.

=== Patchset structure ===
Patch 01~06:    Subpage fixes for compression read path
Patch 07~07:    Support for subpage relocation
Patch 09~16:    Subpage specific fixes and extra limitations
Patch 17:       Enable subpage support
Patch 18:       Subpage specific write path fix

=== Changelog ===
v2:
- Rebased to latest misc-next
   Now metadata write patches are removed from the series, as they are
   already merged into misc-next.

- Added new Reviewed-by/Tested-by/Reported-by tags

- Use separate endio functions to subpage metadata write path

- Re-order the patches, to make refactors at the top of the series
   One refactor, the submit_extent_page() one, should benefit 4K page
   size more than 64K page size, thus it's worthy to be merged early

- New bug fixes exposed by Ritesh Harjani on Power

- Reject RAID56 completely
   Exposed by btrfs test group, which caused BUG_ON() for various sites.
   Considering RAID56 is already not considered safe, it's better to
   reject them completely for now.

- Fix subpage scrub repair failure
   Caused by hardcoded PAGE_SIZE

- Fix free space cache inode size
   Same cause as scrub repair failure

v3:
- Rebased to remove write path prepration patches

- Properly enable btrfs defrag
   Previsouly, btrfs defrag is in fact just disabled.
   This makes tons of tests in btrfs/defrag to fail.

- More bug fixes for rare race/crashes
   * Fix relocation false alert on csum mismatch
   * Fix relocation data corruption
   * Fix a rare case of false ASSERT()
     The fix already get merged into the prepration patches, thus no
     longer in this patchset though.

   Mostly reported by Ritesh from IBM.

v4:
- Disable subpage defrag completely
   As full page defrag can race with fsstress in btrfs/062, causing
   strange ordered extent bugs.
   The full subpage defrag will be submitted as an indepdent patchset.

v5:
- Rebased to latest misc-next branch

v6:
- Rebased to latest misc-next branch
   The 11 existing patches have no conflicts at all.

- Added four patches related to compression read path
   This involves:
   * One small fix for extent map grabbing
   * One preparation to remove GFP_HIGHMEM
     kmap()/kunmap() is not removed yet, as it's only for later
     subpage related decompression path rework.
   * Rework btrfs_decompress_buf2page() and lzo_decompress_bio()
     btrfs_decompress_buf2page() handles the copying of decompressed data
     to inode pages, without proper subpage handling, we can copy
     decompressed data to wrong location
     lzo_decompress_bio() needs a sectorsize related fix to handle
     padding zeros.
     Since we're here, I just reworked the code to make more rooms for
     proper comments.

     These two rework looks scary, and touches the core functions of
     compression, thus Josef gave me extra tests runs on them and no
     regression found.

     But still they definitely deserve more review.

v7:
- Rebased to latest misc-next branch
   With HIGHMEM cleanup already in misc-next, one patch can be dropped.

   With extra Reviewed-by: tags and fixes.

- Added 3 more fixes for subpage compression read path:
   * Sticky @this_bio_flag
     Preivoulys in btrfs_do_readpage() @this_bio_flag is only used once
     as one page only contains one sector.
     But for subpage case, we need to reset this flag, or after reading
     one compressed extent, next uncompressed extent will be treated as
     compressed and causing problems.

   * NULL pointer fix for csum verification for compressed extent
     For compressed extent, we rely on PageChecked to skip csum
     verification for compressed read.
     But that flag only works for full page, no subpage helper yet.
     Thankfully we can easily skip compressed read as it never populate
     io_bio::csum.

   * Disable readahead for compressed read
     It will be properly enabled in write path, since for 64K page size,
     we at most readahead two pages, the readahead is way less effective,
     and we can afford to skip the readahead completely for subpage case.

v8:
- Rebased to latest misc-next branch
   No conflicts

- Add a new hotfix to make __extent_writepage() to ignore IO error
   To enhance the error handling for subpage write path.
   As subpage adds new cases to trigger the error branch while IO errors
   are already handled by bio, no need to error out early and trigger
   another existing (but harder to fix) bug in write path.

Qu Wenruo (18):
   btrfs: properly reset @this_bio_flag in btrfs_do_readpage() to avoid
     inheriting old bio flags to next extent
   btrfs: fix NULL pointer dereference when reading two compressed extent
     inside the same page
   btrfs: disable compressed readahead for subpage
   btrfs: grab correct extent map for subpage compressed extent read
   btrfs: rework btrfs_decompress_buf2page()
   btrfs: rework lzo_decompress_bio() to make it subpage compatible
   btrfs: extract relocation page read and dirty part into its own
     function
   btrfs: make relocate_one_page() to handle subpage case
   btrfs: fix wild subpage writeback which does not have ordered extent.
   btrfs: disable inline extent creation for subpage
   btrfs: allow submit_extent_page() to do bio split for subpage
   btrfs: reject raid5/6 fs for subpage
   btrfs: fix a crash caused by race between prepare_pages() and
     btrfs_releasepage()
   btrfs: fix a use-after-free bug in writeback subpage helper
   btrfs: fix a subpage false alert for relocating partial preallocated
     data extents
   btrfs: fix a subpage relocation data corruption
   btrfs: allow read-write for 4K sectorsize on 64K page size systems
   btrfs: unify the error paths in __extent_writepage() for subpage and
     regular sectorsize

  fs/btrfs/compression.c | 160 +++++++++++----------
  fs/btrfs/compression.h |   5 +-
  fs/btrfs/disk-io.c     |  13 +-
  fs/btrfs/extent_io.c   | 262 ++++++++++++++++++++++++++---------
  fs/btrfs/file.c        |  13 +-
  fs/btrfs/inode.c       |  92 ++++++++++--
  fs/btrfs/ioctl.c       |   6 +
  fs/btrfs/lzo.c         | 196 ++++++++++++--------------
  fs/btrfs/relocation.c  | 308 +++++++++++++++++++++++++++--------------
  fs/btrfs/subpage.c     |  20 ++-
  fs/btrfs/subpage.h     |   7 +
  fs/btrfs/super.c       |   7 -
  fs/btrfs/sysfs.c       |   5 +
  fs/btrfs/volumes.c     |   7 +
  fs/btrfs/zlib.c        |  12 +-
  fs/btrfs/zstd.c        |   6 +-
  16 files changed, 720 insertions(+), 399 deletions(-)

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2.32.0