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From: Paolo Bonzini <pbonzini@redhat.com>
To: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Igor Mammedov <imammedo@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] KVM: Use atomic_long_cmpxchg() instead of an open-coded variant
Date: Fri, 26 Nov 2021 11:34:28 +0100	[thread overview]
Message-ID: <14e0bf75-27f4-83ec-d52f-82d7d4dab5a7@redhat.com> (raw)
In-Reply-To: <7bdc7ee3dcc09a109cfaf9fb8662fb49ca0bec2c.1637884349.git.maciej.szmigiero@oracle.com>

On 11/26/21 01:31, Maciej S. Szmigiero wrote:
> -		if ((long)old == atomic_long_read(&slots->last_used_slot))
> -			atomic_long_set(&slots->last_used_slot, (long)new);
> +		/*
> +		 * The atomicity isn't strictly required here since we are
> +		 * operating on an inactive memslots set anyway.
> +		 */
> +		atomic_long_cmpxchg(&slots->last_used_slot,
> +				    (unsigned long)old, (unsigned long)new);

I think using read/set is more readable than a comment saying that 
atomicity is not required.

It's a fairly common pattern, and while I agree that it's a PITA to 
write atomic_long_read and atomic_long_set, the person that reads the 
code is also helped by read/set, because they know they have to think 
about ownership invariants rather than concurrency invariants.

Paolo


  reply	other threads:[~2021-11-26 10:36 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-26  0:31 [PATCH 0/3] KVM: Scalable memslots implementation additional patches Maciej S. Szmigiero
2021-11-26  0:31 ` [PATCH 1/3] KVM: x86: Avoid overflowing nr_mmu_pages in kvm_arch_commit_memory_region() Maciej S. Szmigiero
2021-11-29 21:03   ` Sean Christopherson
2021-11-26  0:31 ` [PATCH 2/3] KVM: Use atomic_long_cmpxchg() instead of an open-coded variant Maciej S. Szmigiero
2021-11-26 10:34   ` Paolo Bonzini [this message]
2021-11-26  0:31 ` [PATCH 3/3] KVM: Make kvm_for_each_memslot_in_gfn_range() strict and use iterators Maciej S. Szmigiero
2021-11-26 10:35 ` [PATCH 0/3] KVM: Scalable memslots implementation additional patches Paolo Bonzini
2021-11-26 13:18   ` Maciej S. Szmigiero
2021-11-26 13:19     ` Paolo Bonzini

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