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Message-ID: <YuXyKh8Zvr56rR4R@google.com> Date: Sat, 30 Jul 2022 20:08:26 -0700 From: Jaegeuk Kim <jaegeuk@...nel.org> To: Eric Biggers <ebiggers@...nel.org> Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org, linux-api@...r.kernel.org, linux-fscrypt@...r.kernel.org, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, Keith Busch <kbusch@...nel.org> Subject: Re: [PATCH v4 6/9] f2fs: don't allow DIO reads but not DIO writes On 07/25, Eric Biggers wrote: > On Sat, Jul 23, 2022 at 07:01:59PM -0700, Jaegeuk Kim wrote: > > On 07/22, Eric Biggers wrote: > > > From: Eric Biggers <ebiggers@...gle.com> > > > > > > Currently, if an f2fs filesystem is mounted with the mode=lfs and > > > io_bits mount options, DIO reads are allowed but DIO writes are not. > > > Allowing DIO reads but not DIO writes is an unusual restriction, which > > > is likely to be surprising to applications, namely any application that > > > both reads and writes from a file (using O_DIRECT). This behavior is > > > also incompatible with the proposed STATX_DIOALIGN extension to statx. > > > Given this, let's drop the support for DIO reads in this configuration. > > > > IIRC, we allowed DIO reads since applications complained a lower performance. > > So, I'm afraid this change will make another confusion to users. Could > > you please apply the new bahavior only for STATX_DIOALIGN? > > > > Well, the issue is that the proposed STATX_DIOALIGN fields cannot represent this > weird case where DIO reads are allowed but not DIO writes. So the question is > whether this case actually matters, in which case we should make STATX_DIOALIGN > distinguish between DIO reads and DIO writes, or whether it's some odd edge case > that doesn't really matter, in which case we could just fix it or make > STATX_DIOALIGN report that DIO is unsupported. I was hoping that you had some > insight here. What sort of applications want DIO reads but not DIO writes? > Is this common at all? I think there's no specific application to use the LFS mode at this moment, but I'd like to allow DIO read for zoned device which will be used for Android devices. > > - Eric
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