linux-kernel - Re: [PATCH v6 05/11] mm: Add fast_only bool to test_young and clear

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Message-ID: <37ae59f2-777a-4a58-ae58-4a20066364dd@redhat.com>
Date: Thu, 1 Aug 2024 11:36:14 +0200
From: David Hildenbrand <david@...hat.com>
To: James Houghton <jthoughton@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: Ankit Agrawal <ankita@...dia.com>,
 Axel Rasmussen <axelrasmussen@...gle.com>,
 Catalin Marinas <catalin.marinas@....com>,
 David Matlack <dmatlack@...gle.com>, David Rientjes <rientjes@...gle.com>,
 James Morse <james.morse@....com>, Jason Gunthorpe <jgg@...pe.ca>,
 Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oliver.upton@...ux.dev>,
 Raghavendra Rao Ananta <rananta@...gle.com>,
 Ryan Roberts <ryan.roberts@....com>, Sean Christopherson
 <seanjc@...gle.com>, Shaoqin Huang <shahuang@...hat.com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Wei Xu <weixugc@...gle.com>,
 Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
 Zenghui Yu <yuzenghui@...wei.com>, kvmarm@...ts.linux.dev,
 kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v6 05/11] mm: Add fast_only bool to test_young and
 clear_young MMU notifiers

On 24.07.24 03:10, James Houghton wrote:
> For implementers, the fast_only bool indicates that the age information
> needs to be harvested such that we do not slow down other MMU operations,
> and ideally that we are not ourselves slowed down by other MMU
> operations.  Usually this means that the implementation should be
> lockless.

But what are the semantics if "fast_only" cannot be achieved by the 
implementer?

Can we add some documentation to the new functions that explain what 
this mysterious "fast_only" is and what the expected semantics are? 
Please? :)

-- 
Cheers,

David / dhildenb