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From: Christoph Hellwig <hch@infradead.org>
To: Keith Busch <kbusch@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
	Sean Anderson <seanga2@gmail.com>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	linux-mtd@lists.infradead.org,
	Zhihao Cheng <chengzhihao1@huawei.com>
Subject: Re: bio segment constraints
Date: Mon, 7 Apr 2025 06:59:55 -0700	[thread overview]
Message-ID: <Z_PaW2QS3OXTXHSO@infradead.org> (raw)
In-Reply-To: <Z_PXONJyuv4Z8ATr@kbusch-mbp>

On Mon, Apr 07, 2025 at 02:46:32PM +0100, Keith Busch wrote:
> > > - Is is possible to have segments not even aligned to SECTOR_SIZE?
> > 
> > No.
> 
> O_DIRECT only requires each user iovec be a multiple of the logical
> block size with the address aligned to the dma_alignment. If the
> dma_alignment is smaller than the logical block size, then this could
> create bvec segments that are smaller. For nvme where we have 4-byte
> dma alignment, you could have the first segment be the last 4 bytes of a
> page, then the remaing 508 bytes from a different page in the next
> segment.

Oh, right - with a smaller dma alignment this can actually happen.


WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Keith Busch <kbusch@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
	Sean Anderson <seanga2@gmail.com>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	linux-mtd@lists.infradead.org,
	Zhihao Cheng <chengzhihao1@huawei.com>
Subject: Re: bio segment constraints
Date: Mon, 7 Apr 2025 06:59:55 -0700	[thread overview]
Message-ID: <Z_PaW2QS3OXTXHSO@infradead.org> (raw)
In-Reply-To: <Z_PXONJyuv4Z8ATr@kbusch-mbp>

On Mon, Apr 07, 2025 at 02:46:32PM +0100, Keith Busch wrote:
> > > - Is is possible to have segments not even aligned to SECTOR_SIZE?
> > 
> > No.
> 
> O_DIRECT only requires each user iovec be a multiple of the logical
> block size with the address aligned to the dma_alignment. If the
> dma_alignment is smaller than the logical block size, then this could
> create bvec segments that are smaller. For nvme where we have 4-byte
> dma alignment, you could have the first segment be the last 4 bytes of a
> page, then the remaing 508 bytes from a different page in the next
> segment.

Oh, right - with a smaller dma alignment this can actually happen.


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Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

  reply	other threads:[~2025-04-07 13:59 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-04-06 19:40 bio segment constraints Sean Anderson
2025-04-06 19:40 ` Sean Anderson
2025-04-07  7:07 ` Christoph Hellwig
2025-04-07  7:07   ` Christoph Hellwig
2025-04-07 13:46   ` Keith Busch
2025-04-07 13:46     ` Keith Busch
2025-04-07 13:59     ` Christoph Hellwig [this message]
2025-04-07 13:59       ` Christoph Hellwig
2025-04-07 15:52       ` Bart Van Assche
2025-04-07 15:52         ` Bart Van Assche
2025-04-07 13:59   ` Sean Anderson
2025-04-07 13:59     ` Sean Anderson
2025-04-07 14:12     ` Christoph Hellwig
2025-04-07 14:12       ` Christoph Hellwig
2025-04-07  7:10 ` Hannes Reinecke
2025-04-07  7:10   ` Hannes Reinecke
2025-04-07 14:14   ` Sean Anderson
2025-04-07 14:14     ` Sean Anderson
2025-04-08  6:10     ` Hannes Reinecke
2025-04-08  6:10       ` Hannes Reinecke
2025-04-08 13:57       ` Sean Anderson
2025-04-08 13:57         ` Sean Anderson
2025-04-08 14:33     ` Keith Busch
2025-04-08 14:33       ` Keith Busch

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