linux-kernel - Re: [PATCH v21 1/4] mm: add VM_DROPPABLE for designating always lazily freeable mappings

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Message-ID: <Zovuwesu_RaSixe6@zx2c4.com>
Date: Mon, 8 Jul 2024 15:50:57 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.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 v21 1/4] mm: add VM_DROPPABLE for designating always
 lazily freeable mappings

Hi Linus,

On Sun, Jul 07, 2024 at 05:08:29PM -0700, Linus Torvalds wrote:
>    +                    vm_flags |= VM_DROPPABLE;
>    +                    vm_flags |= VM_WIPEONFORK | VM_DONTDUMP;
> which looks rather simple.

That is nice, though I would add that if we're implying things that are
sensible to imply, it really also needs to add VM_NORESERVE too.
DROPPABLE doesn't make sense semantically without it.

Anyway, rather than adding PROT_xyz for v+1, I'll try adding this
MAP_DROPPABLE (or a different name for David) with the implications as
you've suggested.

Jason