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Date: Tue, 29 Oct 2024 16:26:54 +0100
From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@meta.com>
Cc: linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-scsi@vger.kernel.org, io-uring@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, hch@lst.de, joshi.k@samsung.com,
	javier.gonz@samsung.com, bvanassche@acm.org,
	Keith Busch <kbusch@kernel.org>, Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCHv10 9/9] scsi: set permanent stream count in block limits
Message-ID: <20241029152654.GC26431@lst.de>
References: <20241029151922.459139-1-kbusch@meta.com> <20241029151922.459139-10-kbusch@meta.com>
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On Tue, Oct 29, 2024 at 08:19:22AM -0700, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
> 
> The block limits exports the number of write hints, so set this limit if
> the device reports support for the lifetime hints. Not only does this
> inform the user of which hints are possible, it also allows scsi devices
> supporting the feature to utilize the full range through raw block
> device direct-io.
> 
> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Keith Busch <kbusch@kernel.org>

Despite the reviews this is still incorrect.  The permanent streams have
a relative data temperature associated with them as pointed out last
round and are not arbitrary write stream contexts despite (ab)using
the SBC streams facilities.

Bart, btw: I think the current sd implementation is buggy as well, as
it assumes the permanent streams are ordered by their data temperature
in the IO Advise hints mode page, but I can't find anything in the
spec that requires a particular ordering.