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

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Message-ID: <CAHk-=wjVc6cpSCJwAqrhPvwBbcQEOL2TEnCELfadhA=n1GN4Ww@mail.gmail.com>
Date: Thu, 11 Jul 2024 12:17:40 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: David Hildenbrand <david@...hat.com>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>, 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, 11 Jul 2024 at 12:08, David Hildenbrand <david@...hat.com> wrote:
>
> We also have these folio_mark_dirty() calls, for example in
> unpin_user_pages_dirty_lock(). Hm ... so preventing the folio from
> getting dirtied is likely shaky.

I do wonder if we should just disallow page pinning for these pages
entirely. When the page can get replaced by zeroes at any time,
pinning it doesn't make much sense.

Except we do have that whole "fast" case that intentionally doesn't
take locks and doesn't have a vma. Darn.

             Linus