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

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Message-ID: <75cf01cd-8a45-4a79-b06c-cdf2d68cdd53@redhat.com>
Date: Mon, 8 Jul 2024 22:06:43 +0200
From: David Hildenbrand <david@...hat.com>
To: "Jason A. Donenfeld" <Jason@...c4.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 v21 1/4] mm: add VM_DROPPABLE for designating always
 lazily freeable mappings

On 08.07.24 15:55, Jason A. Donenfeld wrote:
> Hi David,
> 
> On Mon, Jul 08, 2024 at 10:11:24AM +0200, David Hildenbrand wrote:
>> The semantics are much more intuitive. No need for separate mmap flags.
> 
> Agreed.
>   
>> Likely we'll have to adjust mlock() as well. Also, I think we should
>> just bail out with hugetlb as well.
> 
> Ack.
> 
>> Further, maybe we want to disallow madvise() clearing these flags here,
>> just to be consistent.
> 
> Good thinking.
> 
>> As a side note, I'll raise that I am not a particular fan of the
>> "droppable" terminology, at least with the "read 0s" approach.
>>
>>   From a user perspective, the memory might suddenly lose its state and
>> read as 0s just like volatile memory when it loses power. "dropping
>> pages" sounds more like an implementation detail.
>>
>> Something like MAP_VOLATILE might be more intuitive (similar to the
>> proposed MADV_VOLATILE).
>>
>> But naming is hard, just mentioning to share my thought :)
> 
> Naming is hard, but *renaming* is annoying. I like droppable simply
> because that's what I've been calling it in my head. MAP_VOLATILE is
> fine with me though, and seems reasonable enough. So I'll name it that,
> and then please don't change your mind about it later so I won't have to
> rename everything again. :)

:) Nah. But wait with any remaining until more than one person thinks 
it's a good idea.

-- 
Cheers,

David / dhildenb