linux-kernel - Re: bio_vec, bv

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Message-ID: <ZZPkV2KU/dHvBB3d@casper.infradead.org>
Date: Tue, 2 Jan 2024 10:24:23 +0000
From: Matthew Wilcox <willy@...radead.org>
To: David Howells <dhowells@...hat.com>
Cc: Christoph Hellwig <hch@....de>, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: bio_vec, bv_page and folios

On Tue, Jan 02, 2024 at 10:03:58AM +0000, David Howells wrote:
> Matthew Wilcox <willy@...radead.org> wrote:
> 
> > On Tue, Jan 02, 2024 at 08:56:46AM +0000, David Howells wrote:
> > > Hi Christoph, Willy,
> > > 
> > > Will bv_page in struct bio_vec ever become a folio pointer rather than I page
> > > pointer?  I'm guessing not as it still presumably needs to be able to point to
> > > non-folio pages.
> > 
> > My plan for bio_vec is that it becomes phyr -- a physical address +
> > length.  No more page or folio reference.
> 
> Interesting...  What does that mean for those places that currently use
> bv_page as a place to stash a pointer to the page and use it to clean up the
> page later?

I don't intend to get rid of bio_for_each_folio_all() or bio_add_page()
for example.  It's just a phys_to_page() away.  The advantage is that
we wouldn't need a struct page to do I/O to a physical address.