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From: David Hildenbrand <david@redhat.com>
To: David Howells <dhowells@redhat.com>,
	torvalds@linux-foundation.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>,
	Theodore Ts'o <tytso@mit.edu>,
	Christoph Hellwig <hch@infradead.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Vlastimil Babka <vbabka@suse.cz>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Jeff Layton <jlayton@kernel.org>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: Folios: Can we resolve this please?
Date: Wed, 1 Sep 2021 12:18:13 +0200	[thread overview]
Message-ID: <3c0833bd-4731-aeb2-e9d4-bd480276ae6c@redhat.com> (raw)
In-Reply-To: <3285174.1630448147@warthog.procyon.org.uk>

On 01.09.21 00:15, David Howells wrote:
> Hi Linus, Andrew, Johannes,
> 
> Can we come to a quick resolution on folios?  I'd really like this to be
> solved in this merge window if at all possible as I (and others) have stuff
> that will depend on and will conflict with Willy's folio work.  It would be
> great to get this sorted one way or another.
> 
> As I see it, there are three issues, I think, and I think they kind of go like
> this:
> 
>   (1) Johannes wants to get away from pages being used as the unit of memory
>       currency and thinks that folios aren't helpful in this regard[1].  There
>       seems to be some disagreement about where this is heading.
> 
>   (2) Linus isn't entirely keen on Willy's approach[2], with a bottom up
>       approach hiding the page objects behind a new type from the pov of the
>       filesystem, but would rather see the page struct stay the main API type
>       and the changes be hidden transparently inside of that.
> 
>       I think from what Linus said, he may be in favour (if that's not too
>       strong a word) of using a new type to make sure we don't miss the
>       necessary changes[3].
> 
>   (3) Linus isn't in favour of the name 'folio' for the new type[2].  Various
>       names have been bandied around and Linus seems okay with "pageset"[4],
>       though it's already in minor(-ish) use[5][6].  Willy has an alternate
>       patchset with "folio" changed to "pageset"[7].
> 
> With regard to (1), I think the folio concept could be used in future to hide
> at least some of the paginess from filesystems.
> 
> With regard to (2), I think a top-down approach won't work until and unless we
> wrap all accesses to struct page by filesystems (and device drivers) in
> wrapper functions - we need to stop filesystems fiddling with page internals
> because what page internals may mean may change.
> 
> With regard to (3), I'm personally fine with the name "folio", as are other
> people[8][9][10][11], but I could also live with a conversion to "pageset".
> 
> Is it possible to take the folios patchset as-is and just live with the name,
> or just take Willy's rename-job (although it hasn't had linux-next soak time
> yet)?  Or is the approach fundamentally flawed and in need of redoing?

Whatever we do, it would be great to get it out of -next one way (merge) 
or the other (drop) ASAP, as it's a lot of code churn, affecting various 
subsystems.

But merging it in a (for some people) suboptimal state just to get it 
out of -next might not necessarily be what we want.

-- 
Thanks,

David / dhildenb


  parent reply	other threads:[~2021-09-01 10:18 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-31 22:15 Folios: Can we resolve this please? David Howells
2021-09-01 10:18 ` David Hildenbrand
2021-09-01 10:18 ` David Hildenbrand [this message]
2021-09-01 11:42 ` Christian Brauner

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