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

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Message-ID: <20240501231533.3128797-1-bongiojp@gmail.com>
Date: Wed,  1 May 2024 16:15:32 -0700
From: Jeremy Bongio <bongiojp@...il.com>
To: Ted Tso <tytso@....edu>
Cc: linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-api@...r.kernel.org,
	linux-block@...r.kernel.org,
	Jeremy Bongio <jbongio@...gle.com>
Subject: [RFC PATCH 0/1] Change failover behavior for DIRECT writes in ext4/block fops

From: Jeremy Bongio <jbongio@...gle.com>

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(-)

-- 
2.44.0.769.g3c40516874-goog