On Sun, May 30, 2021 at 9:45 PM Su Yue [off-list ref] wrote:

On Sun 30 May 2021 at 08:12, Neal Gompa [off-list ref]
wrote:

quoted

On Fri, May 21, 2021 at 5:56 AM Qu Wenruo [off-list ref] wrote:

quoted

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

=== 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.
(As the btrfs defrag group doesn't require that restrict defrag
result,
btrfs/defrag group also passes here)

For anyone who is interested in testing, please apply this
patch for
btrfs-progs before testing.
https://patchwork.kernel.org/project/linux-btrfs/patch/20210420073036.243715-1-wqu@suse.com/
Or there will be too many false alerts.

=== 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.
  Thus for current patchset, no matter what inode attribute or
  mount
  option is, no new compressed extent can be created for
  subpage case.

- 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.

- 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 sector-sized defrag support
  Currently defrag is still done in PAGE_SIZE, meaning if there
  is a
  hole in a 64K page, we still write a full 64K back to disk.
  This causes more disk space usage.

=== Patchset structure ===

Patch 01~19:    Make data write path to be subpage compatible
Patch 20~21:    Make data relocation path to be subpage
compatible
Patch 22~30:    Various fixes for subpage corner cases
Patch 31:       Enable subpage data write

=== 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.

Qu Wenruo (31):
  btrfs: pass bytenr directly to __process_pages_contig()
  btrfs: refactor the page status update into
  process_one_page()
  btrfs: provide btrfs_page_clamp_*() helpers
  btrfs: only require sector size alignment for
    end_bio_extent_writepage()
  btrfs: make btrfs_dirty_pages() to be subpage compatible
  btrfs: make __process_pages_contig() to handle subpage
    dirty/error/writeback status
  btrfs: make end_bio_extent_writepage() to be subpage
  compatible
  btrfs: make process_one_page() to handle subpage locking
  btrfs: introduce helpers for subpage ordered status
  btrfs: make page Ordered bit to be subpage compatible
  btrfs: update locked page dirty/writeback/error bits in
    __process_pages_contig
  btrfs: prevent extent_clear_unlock_delalloc() to unlock page
  not
    locked by __process_pages_contig()
  btrfs: make btrfs_set_range_writeback() subpage compatible
  btrfs: make __extent_writepage_io() only submit dirty range
  for
    subpage
  btrfs: make btrfs_truncate_block() to be subpage compatible
  btrfs: make btrfs_page_mkwrite() to be subpage compatible
  btrfs: reflink: make copy_inline_to_page() to be subpage
  compatible
  btrfs: fix the filemap_range_has_page() call in
    btrfs_punch_hole_lock_range()
  btrfs: don't clear page extent mapped if we're not
  invalidating the
    full page
  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: make defrag to be semi subpage compatible
  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

 fs/btrfs/ctree.h        |   2 +-
 fs/btrfs/disk-io.c      |  13 +-
 fs/btrfs/extent_io.c    | 551
 +++++++++++++++++++++++++++-------------
 fs/btrfs/file.c         |  31 ++-
 fs/btrfs/inode.c        | 147 +++++++++--
 fs/btrfs/ioctl.c        |  12 +-
 fs/btrfs/ordered-data.c |   5 +-
 fs/btrfs/reflink.c      |  14 +-
 fs/btrfs/relocation.c   | 287 +++++++++++++--------
 fs/btrfs/subpage.c      | 156 +++++++++++-
 fs/btrfs/subpage.h      |  31 +++
 fs/btrfs/super.c        |   7 -
 fs/btrfs/sysfs.c        |   5 +
 fs/btrfs/volumes.c      |   8 +
 14 files changed, 937 insertions(+), 332 deletions(-)

--
2.31.1

So this seems to have no impact on my system on x86_64 with the
branch, which is good I guess?

Unfortunately, I couldn't make a test package based on 5.13rc4
for
some confidence testing as the patch set from Patchwork doesn't
apply...

However, somewhat related to this, it seems that we're going to
be
seeing a need for 4K <-> 16K page interoperability because Linux
will
need to be configured to use 16K pages to run effectively on
Apple ARM
Mac systems[1][2].

How difficult would it be to extend this to also handle 16K
pages too?
Not necessarily in this patch set, but in a follow-up one?

[1]: https://twitter.com/marcan42/status/1398301930879815680
[2]: https://twitter.com/marcan42/status/1398301933203431426

As a super fan of Apple, I've noticed Hector Martin's work on M1
chip.
I'm so happy to expect a full functional M1 device running on
linux.
However as for btrfs, I'd say just let 64k pagesize subpage
support go
ahead and fix potencial bugs by real users feedbacks for sometime.

I wasn't proposing that we hold this back for that. In fact, I
explicitly suggested *not* doing that. However, it's somewhat academic
for now as M1 support isn't quite done yet, and we still don't have
this merged either.


-- 
真実はいつも一つ！/ Always, there's only one truth!