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tempfile: make sure FS_COMPR_FL stays set

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btrfs will set the FS_NOCOMP_FL flag when all of the following are true:

1.  The filesystem is not mounted with the `compress-force` option
2.  Heuristic analysis of the data suggests the data is compressible
3.  Compression fails to produce a result that is smaller than the original

If the compression ratio is 40%, and the original data is 128K long,
then compressed data will be about 52K long (rounded up to 4K), so item
3 is usually false; however, if the original data is 8K long, then the
compressed data will be 8K long too, and btrfs will set FS_NOCOMP_FL.

To work around that, keep setting FS_COMPR_FL and clearing FS_NOCOMP_FL
every time a TempFile is reset.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell
2025-02-25 03:16:27 -05:00
parent 4039ef229e
commit 3a17a4dcdd
1 changed files with 13 additions and 11 deletions
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24
src/bees.cc
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@ -502,6 +502,19 @@ BeesTempFile::resize(off_t offset)
// Count time spent here
BEESCOUNTADD(tmp_resize_ms, resize_timer.age() * 1000);
// Modify flags - every time
// - btrfs will keep trying to set FS_NOCOMP_FL behind us when compression heuristics identify
// the data as compressible, but it fails to compress
// - clear FS_NOCOW_FL because we can only dedupe between files with the same FS_NOCOW_FL state,
// and we don't open FS_NOCOW_FL files for dedupe.
BEESTRACE("Getting FS_COMPR_FL and FS_NOCOMP_FL on m_fd " << name_fd(m_fd));
int flags = ioctl_iflags_get(m_fd);
flags |= FS_COMPR_FL;
flags &= ~(FS_NOCOMP_FL | FS_NOCOW_FL);
BEESTRACE("Setting FS_COMPR_FL and clearing FS_NOCOMP_FL | FS_NOCOW_FL on m_fd " << name_fd(m_fd) << " flags " << to_hex(flags));
ioctl_iflags_set(m_fd, flags);
// That may have queued some delayed ref deletes, so throttle them
bees_throttle(resize_timer.age(), "tmpfile_resize");
}
@ -543,17 +556,6 @@ BeesTempFile::BeesTempFile(shared_ptr<BeesContext> ctx) :
// Add this file to open_root_ino lookup table
m_roots->insert_tmpfile(m_fd);
// Set compression attribute
BEESTRACE("Getting FS_COMPR_FL on m_fd " << name_fd(m_fd));
int flags = ioctl_iflags_get(m_fd);
flags |= FS_COMPR_FL;
// Clear NOCOW because it conflicts with COMPR, and NOCOW could be set on the root subvol
flags &= FS_NOCOW_FL;
BEESTRACE("Setting FS_COMPR_FL on m_fd " << name_fd(m_fd) << " flags " << to_hex(flags));
ioctl_iflags_set(m_fd, flags);
// Count time spent here
BEESCOUNTADD(tmp_create_ms, create_timer.age() * 1000);