[RFC,0/1] Change failover behavior for DIRECT writes in ext4/block fops

Message

Jeremy Bongio May 1, 2024, 11:15 p.m. UTC

From: Jeremy Bongio <[e-mail]>

In kernel 6.9, for an O_DIRECT write:
xfs - Will fallback to a sync, buffered write for -ENOTBLK (for reflink CoW)
ext2/3/4 - will fallback to a sync, buffered write for short writes.
       If iomap returns -ENOTBLK, write will return status of 0.
block fops - will fallback to a sync, buffered write for short writes.
zonefs - Will fallback to a sync, buffered write for -ENOTBLK.
         Will return the bytes written for a short write, no fallback.

Relevant commit:
60263d5889e6d "iomap: fall back to buffered writes for invalidation failures"

In most cases, I think users would be surprised if an O_DIRECT write request
silently resulted in a buffered request.

The iomap_dio_rw() return code -ENOTBLK means page invalidation failed before
submitting the bio.

Is falling back to buffered IO for short writes or -ENOTBLK desirable in ext4
or block fops?

Jeremy Bongio (1):
  Remove buffered failover for ext4 and block fops direct writes.

 block/fops.c   |  3 ---
 fs/ext4/file.c | 27 ---------------------------
 2 files changed, 30 deletions(-)