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

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Message-ID: <57efaa1f-e9b6-41e8-96d5-aea5bc102bb4@redhat.com>
Date: Thu, 11 Jul 2024 21:22:00 +0200
From: David Hildenbrand <david@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
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 11.07.24 21:17, Linus Torvalds wrote:
> 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.

Yeah, and I think it should all be simpler; we shouldn't have to 
special-case these cases everywhere.

Maybe we can just find a way to not do *folio_set_swapbacked() without a 
VMA.

-- 
Cheers,

David / dhildenb