Re: [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64

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To: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Subject: Re: [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64
From: Christoph Hellwig <hch@xxxxxx>
Date: Thu, 20 Mar 2025 15:18:46 +0100
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, lsf-pc@xxxxxxxxxxxxxxxxxxxxxxxxxx, david@xxxxxxxxxxxxx, leon@xxxxxxxxxx, hch@xxxxxx, kbusch@xxxxxxxxxx, sagi@xxxxxxxxxxx, axboe@xxxxxxxxx, joro@xxxxxxxxxx, brauner@xxxxxxxxxx, hare@xxxxxxx, willy@xxxxxxxxxxxxx, djwong@xxxxxxxxxx, john.g.garry@xxxxxxxxxx, ritesh.list@xxxxxxxxx, p.raghav@xxxxxxxxxxx, gost.dev@xxxxxxxxxxx, da.gomez@xxxxxxxxxxx
In-reply-to: <Z9v-1xjl7dD7Tr-H@bombadil.infradead.org>
User-agent: Mutt/1.5.17 (2007-11-01)

On Thu, Mar 20, 2025 at 04:41:11AM -0700, Luis Chamberlain wrote:
> We've been constrained to a max single 512 KiB IO for a while now on x86_64.

No, we absolutely haven't.  I'm regularly seeing multi-MB I/O on both
SCSI and NVMe setup.

> This is due to the number of DMA segments and the segment size.

In nvme the max_segment_size is UINT_MAX, and for most SCSI HBAs it is
fairly large as well.

Follow-Ups:
- Re: [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64
  - From: Luis Chamberlain
- Re: [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64
  - From: Bart Van Assche

References:
- [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64
  - From: Luis Chamberlain

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