Re: Could it be made possible to offer "supplementary" data to a DIO write ?

Adam Borowski
2021-08-05T18:27:51Z

On Thu, Aug 05, 2021 at 03:38:01PM +0100, David Howells wrote:
> Generally, I prefer to write back the minimum I can get away with (as does the
> Linux NFS client AFAICT).
>
> However, if everyone agrees that we should only ever write back a multiple of
> a certain block size, even to network filesystems, what block size should that
> be? Note that PAGE_SIZE varies across arches and folios are going to
> exacerbate this. What I don't want to happen is that you read from a file, it
> creates, say, a 4M (or larger) folio; you change three bytes and then you're
> forced to write back the entire 4M folio.

grep . /sys/class/block/*/queue/minimum_io_size
and also hw_sector_size, logical_block_size, physical_block_size.

The data seems suspect to me, though. I get 4096 for a spinner (looks
sane), 512 for nvme (less than page size), and 4096 for pmem (I'd expect
cacheline or ECC block).

Meow!
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