linux-kernel - Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always lazily freeable mappings

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Message-ID: <ZpAc118_U7p3u2gZ@zx2c4.com>
Date: Thu, 11 Jul 2024 19:56:39 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: David Hildenbrand <david@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
	tglx@...utronix.de, linux-crypto@...r.kernel.org,
	linux-api@...r.kernel.org, x86@...nel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>,
	Carlos O'Donell <carlos@...hat.com>,
	Florian Weimer <fweimer@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	Jann Horn <jannh@...gle.com>,
	Christian Brauner <brauner@...nel.org>,
	David Hildenbrand <dhildenb@...hat.com>, linux-mm@...ck.org
Subject: Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always
 lazily freeable mappings

On Thu, Jul 11, 2024 at 07:54:34PM +0200, Jason A. Donenfeld wrote:
> On Thu, Jul 11, 2024 at 07:27:27PM +0200, David Hildenbrand wrote:
> > > PG_owner_priv_1 maps to PG_swapcache? :)
> > 
> > Maybe the combination !swapbacked && swapcache could be used to indicate 
> > such folios. (we will never set swapbacked)
> > 
> > But likely we have to be a bit careful here. We don't want 
> > folio_test_swapcache() to return for folios that ... are not in the 
> > swapcache.
> 
> I was thinking that too, but I'm afraid it's going to be another
> whack-a-mole nightmare. Even for things like task_mmu in procfs that
> show stats, that's going to be wonky.
> 
> Any other flags we can overload that aren't going to be already used in
> our case?

PG_error / folio_set_error seems unused in the non-IO case.