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From:   Hans Holmberg <Hans.Holmberg@wdc.com>
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     "hch@infradead.org" <hch@infradead.org>,
        Damien Le Moal <Damien.LeMoal@wdc.com>,
        "chao@kernel.org" <chao@kernel.org>,
        "linux-f2fs-devel@lists.sourceforge.net" 
        <linux-f2fs-devel@lists.sourceforge.net>,
        "hans@owltronix.com" <hans@owltronix.com>,
        Aravind Ramesh <Aravind.Ramesh@wdc.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] f2fs: preserve direct write semantics when buffering
 is forced
Thread-Topic: [RFC PATCH] f2fs: preserve direct write semantics when buffering
 is forced
Thread-Index: AQHZRSW5RGgzfxLfmEqd2IrSayym268D2TwAgAVGSICAAA0xAIAADFcAgAAFugCAAAscgIAEpCYAgG7RPQA=
Date:   Mon, 5 Jun 2023 11:56:39 +0000
Message-ID: <20230605115638.GA23662@gsv>
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On Sun, Mar 26, 2023 at 04:39:10PM -0700, hch@infradead.org wrote:
> On Thu, Mar 23, 2023 at 05:46:37PM -0700, Jaegeuk Kim wrote:
> > > Yes, and that was exactly my point: with LFS mode, O_DIRECT write
> > > should never overwrite anything. So I do not see why direct writes
> > > should be handled as buffered writes with zoned devices. Am I missing
> > > something here ?
> >=20
> > That's an easiest way to serialize block allocation and submit_bio when=
 users
> > are calling buffered writes and direct writes in parallel. :)
> > I just felt that if we can manage both of them in direct write path alo=
ng with
> > buffered write path, we may be able to avoid memcpy.
>=20
> Yes.  Note that right now f2fs doesn't really support proper O_DIRECT
> for buffered I/O either, as non-overwrites require a feature similar
> to unwritten extents, or a split of the allocation phase and the record
> metdata phase.  If we'd go for the second choice for f2fs, which is the
> more elegant thing to do, you'll get the zoned direct I/O write support
> almost for free.

So, Jaegeuk, do you think suporting direct io proper is the way to do to fi=
x this
issue? That looks like a better solution to me (at least long term).

Until that would be put into place, do you want my fix (with your code
style fixes) rebased and resent?

Cheers,
Hans=