linux-kernel - Re: [RFC PATCH 0/2] SKSM: Synchronous Kernel Samepage Merging

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Message-ID: <4705cebb-dc11-4fac-bfcc-74d0cb5af5fc@redhat.com>
Date: Fri, 28 Feb 2025 16:19:23 +0100
From: David Hildenbrand <david@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 Matthew Wilcox <willy@...radead.org>, Olivier Dion <odion@...icios.com>,
 linux-mm@...ck.org
Subject: Re: [RFC PATCH 0/2] SKSM: Synchronous Kernel Samepage Merging

On 28.02.25 16:10, David Hildenbrand wrote:
> On 28.02.25 15:59, Sean Christopherson wrote:
>> On Fri, Feb 28, 2025, David Hildenbrand wrote:
>>> On 28.02.25 06:17, Linus Torvalds wrote:
>>>> On Thu, 27 Feb 2025 at 19:03, Mathieu Desnoyers
>>>> <mathieu.desnoyers@...icios.com> wrote:
>>>>>
>>>>> I'd be fine with SKSM replacing KSM entirely. However, I don't
>>>>> think we should try to re-implement the existing KSM userspace ABIs
>>>>> over SKSM.
>>>>
>>>> No, absolutely. The only point (for me) for your new synchronous one
>>>> would be if it replaced the kernel thread async scanning, which would
>>>> make the old user space interface basically pointless.
>>>>
>>>> But I don't actually know who uses KSM right now. My reaction really
>>>> comes from a "it's not nice code in the kernel", not from any actual
>>>> knowledge of the users.
>>>>
>>>> Maybe it works really well in some cloud VM environment, and we're
>>>> stuck with it forever.
>>>
>>> Exactly that; and besides the VM use-case, lately people stated using it in
>>> the context of interpreters (IIRC inside Meta) quite successfully as well.
>>
>> Does Red Hat (or any other KVM supporters) actually recommend using KSM for VMs
>> in cloud environments?
> 
> Private clouds yes, that's where it is most commonly used for. I would
> assume that nobody for

forgot to complete that sentence: "... nobody really should be using 
that in public clouds."

-- 
Cheers,

David / dhildenb