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Date: Mon, 9 Mar 2026 16:40:47 +0100
From: Christoph Hellwig <hch@lst.de>
To: Kanchan Joshi <joshi.k@samsung.com>
Cc: brauner@kernel.org, hch@lst.de, djwong@kernel.org, jack@suse.cz,
	cem@kernel.org, kbusch@kernel.org, axboe@kernel.dk,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	gost.dev@samsung.com, Hans Holmberg <hans.holmberg@wdc.com>
Subject: Re: [PATCH v2 0/5] write streams and xfs spatial isolation
Message-ID: <20260309154047.GA18538@lst.de>
References: <CGME20260309053425epcas5p32886580a4fbe646ceee66f2864970e9f@epcas5p3.samsung.com> <20260309052944.156054-1-joshi.k@samsung.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

This is laking numbers to justify all the changes.

>From previous experiments the most important isolations is to put
the file system log and metadata into a separate stream each, which
would be the first step before exposing user knobs.

And once we look into application optimizations I think your best bet is
to resurrect the FDP/write streams support for zoned XFS that Hans and I
did and posted in reply to one of Keith' iterations of the write stream
patches.  This will reuse all the intelligent placement decisions we've
put into that allocator.  Once that is done we can look into exposing the
write streams already inherent in that to user space, but we really
should be doing all the ground work first.  And maybe some of this can
apply to the conventional allocator, but given that it has no way to
track the placement unit sizes I'm a bit doubtful that the results will
look great.