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

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Message-ID: <YQwjvlvnBNPJbMwc@angband.pl>
Date:   Thu, 5 Aug 2021 19:45:34 +0200
From:   Adam Borowski <kilobyte@...band.pl>
To:     David Howells <dhowells@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        linux-fsdevel@...r.kernel.org, jlayton@...nel.org,
        Christoph Hellwig <hch@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        dchinner@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Could it be made possible to offer "supplementary" data to a DIO
 write ?

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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