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Date: Thu, 2 May 2024 09:12:21 +0200
From: Christoph Hellwig <hch@lst.de>
To: Kanchan Joshi <joshi.k@samsung.com>
Cc: Christoph Hellwig <hch@lst.de>, axboe@kernel.dk,
	martin.petersen@oracle.com, kbusch@kernel.org, brauner@kernel.org,
	asml.silence@gmail.com, dw@davidwei.uk, io-uring@vger.kernel.org,
	linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
	gost.dev@samsung.com, Anuj Gupta <anuj20.g@samsung.com>
Subject: Re: [PATCH 04/10] block: avoid unpinning/freeing the bio_vec
 incase of cloned bio
Message-ID: <20240502071221.GA31379@lst.de>
References: <20240425183943.6319-1-joshi.k@samsung.com> <CGME20240425184658epcas5p2adb6bf01a5c56ffaac3a55ab57afaf8e@epcas5p2.samsung.com> <20240425183943.6319-5-joshi.k@samsung.com> <20240427070508.GD3873@lst.de> <03cb6ac3-595f-abb1-324b-647ed84cfe6b@samsung.com> <20240429170929.GB31337@lst.de> <ebeca5f1-8d80-e4d4-cf45-9a14ef1413a5@samsung.com>
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On Wed, May 01, 2024 at 06:32:45PM +0530, Kanchan Joshi wrote:
> Can you please tell what function(s) in bio data path that need this 
> conversion?
> To me data path handling seems similar. Each cloned bio will lead to 
> some amount of data transfer to pinned user-memory. The same is 
> happening for meta transfer here.

Well, everywhere.  e.g. for direct I/O everything is just driven from
the fs/direct-io.c and and fs/iomap/direct-io.c code without any
knowledge in the underlying driver if data has been pinned (no bounce
buffering in this case).  Or for passthrough I/O none of the underlying
logic knows about the pinning or bounce buffering, everything is handled
in block/blk-map.c.