linux-kernel - Re: [PATCH 05/12] iomap: Introduce IOMAP

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Message-ID: <ZwehmQt52_iSMLeL@infradead.org>
Date: Thu, 10 Oct 2024 02:42:49 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Goldwyn Rodrigues <rgoldwyn@...e.com>,
	Ritesh Harjani <ritesh.list@...il.com>
Subject: Re: [PATCH 05/12] iomap: Introduce IOMAP_ENCODED

On Tue, Oct 08, 2024 at 02:48:43AM -0700, Christoph Hellwig wrote:
> In general I'm not a huge fan of the encoded magic here, but I'll
> need to take a closer look at the caller if I can come up with
> something better.

I looked a bit more at the code.  I'm not entirely sure I fully
understand it yet, but:

I think most of the read side special casing would be handled by
always submitting the bio at the end of an iomap.  Ritesh was
looking into that for supporting ext2-like file systems that
read indirect block ondemand, but I think it actually is fundamentally
the right thing to do anyway.

For the write we plan to add a new IOMAP_BOUNDARY flag to prevent
merges as part of the XFS RT group series, and I think this should
also solve your problems with keeping one bio per iomap?  The
current patch is here:

https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?h=djwong-wtf&id=91b5d7a52dab63732aee451bba0db315ae9bd09b