linux-kernel - Re: [PATCH] mm/filemap: allocate folios according to the blocksize

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Message-ID: <20230422001454.GQ447837@dread.disaster.area>
Date:   Sat, 22 Apr 2023 10:14:54 +1000
From:   Dave Chinner <david@...morbit.com>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Pankaj Raghav <p.raghav@...sung.com>,
        Hannes Reinecke <hare@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        mcgrof@...nel.org, SSDR Gost Dev <gost.dev@...sung.com>
Subject: Re: [PATCH] mm/filemap: allocate folios according to the blocksize

On Thu, Apr 20, 2023 at 08:03:55AM -0700, Darrick J. Wong wrote:
> On Thu, Apr 20, 2023 at 02:28:36PM +0200, Pankaj Raghav wrote:
> > On 2023-04-20 14:19, Hannes Reinecke wrote:
> > >>
> > >> **Questions on the future work**:
> > >>
> > >> As willy pointed out, we have to do this `order = mapping->host->i_blkbits - PAGE_SHIFT` in
> > >> many places. Should we pursue something that willy suggested: encapsulating order in the
> > >> mapping->flags as a next step?[1]
> > >>
> > >>
> > >> [1] https://lore.kernel.org/lkml/ZDty+PQfHkrGBojn@casper.infradead.org/
> 
> I wouldn't mind XFS gaining a means to control folio sizes, personally.
> At least that would make it easier to explore things like copy on write
> with large weird file allocation unit sizes (2MB, 28k, etc).

[random historical musings follow]

Ah, how things go full circle. This is how XFS originally worked on
Irix - it had read and write IO sizes that it used to control the
size of buffers allocated ifor caching data in the per-inode chunk
cache. That stuff was in the original port to Linux, we even had a
mount option to allow users to determine preferred IO sizes
(biosize) but that was removed in 2019 ago because it hadn't
done anything for more than a decade.

That was done around the same time the mp->m_readio_blocks and
mp->m_writeio_blocks variables that it originally influenced were
removed.  Extent allocation sizes are still influenced this way by
the allocsize mount option and m_writeio_blocks was renamed
m_allocsize_blocks to keep this functionality for extent
allocation...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com