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Date: Thu, 20 Mar 2025 15:54:49 +0100
From: Christoph Hellwig <hch@lst.de>
To: Daniel Gomez <da.gomez@kernel.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-block@vger.kernel.org,
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Subject: Re: [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64
Message-ID: <20250320145449.GA14191@lst.de>
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On Thu, Mar 20, 2025 at 02:47:22PM +0100, Daniel Gomez wrote:
> On Thu, Mar 20, 2025 at 04:41:11AM +0100, Luis Chamberlain wrote:
> > We've been constrained to a max single 512 KiB IO for a while now on x86_64.
> > This is due to the number of DMA segments and the segment size. With LBS the
> > segments can be much bigger without using huge pages, and so on a 64 KiB
> > block size filesystem you can now see 2 MiB IOs when using buffered IO.
> 
> Actually up to 8 MiB I/O with 64k filesystem block size with buffered I/O
> as we can describe up to 128 segments at 64k size.

Block layer segments are in no way limited to the logical block size.