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t=1789034950; bh=b9PGX3cvQTKEp1StomMC/PUuNY3LIk1gdRQb5hd00+M=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=BAOxyzNVBmdk0w4Ok8N6GqK+3kwon4WEcnxstz+r/TqzWTPlAHxm+HOGFc01l/A77 RQTg3M3ldGn4sB9a9QHOqudnvyDNwWz4Qvp+9FfBqU5zxaRIQTIQ48juQh+1laj8sL w/5VaC34duOFKT4kTvGC9QsZO1IwYZsuFzjo7XJTUUkViDCw4cZgBrjT+HU2g3+oOI IuwbNPTaPc87hlZ24/4dYFFFL+bl+5rg79QkXtq56ZKwhU4YPOIcGG8SLKPpEi5csw HU6JWoPT4olrK0Xm5qRwntLlk5vV6MU9bPsYT5MHC/mlTY9BxWf53tdHfC41G9ngs8 xEfpJ+9TdcOhQ== Message-ID: Date: Thu, 10 Sep 2026 12:09:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 1/5] mm: Make per-VMA locks available universally To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: dave.hansen@linux.intel.com, Liam.Howlett@oracle.com, ljs@kernel.org, willy@infradead.org, shakeel.butt@linux.dev, vbabka@kernel.org, jannh@google.com, aliceryhl@google.com, arve@android.com, cmllamas@google.com, christian@brauner.io, tkjos@android.com, dsahern@kernel.org, davem@davemloft.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org References: <20260831203056.838265-1-surenb@google.com> <20260831203056.838265-2-surenb@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 8086E100009 X-Rspam-User: X-Stat-Signature: zsxgr7nen7c77shjqisbk15439cu665o X-HE-Tag: 1789034951-818845 X-HE-Meta: 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 gMJjPt5e oWIGXGojG8X2F1in8LMIxzXXQ3laNRbEXz2q9IvWu+ntYAMkscYceJgNZNMm/4PJZnCcmDJPgSlaovBqgoXV4Fsigxi5nv0yjGOmH+XzAjAjn5Lh4PxUx85opsV9l/Q8RRZSBRI1FfrJKZjoiHrBleFW8+AJrajpKJX8ljNOxA9LpSOzHIUKNQUrSXHpuHKCIBSQzKnvOrW1RyO4oxle+WYjX8FZpRcep5Z2yRmyGgHsV/zi54S4/Jy6w/TbtHAkxZFDLFYmXOQKaFwaf89lLPHqvxHHhEkR5f0aXQIldasCPpgtxxxVhBkjf/uY4lXmjod2u0Dr9uk1h0lota98wTMmQX/GxChcIqMzMfK80AqDo1XEeNE3JH0QDAV0tnZ9L2+tq Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/31/26 22:30, Suren Baghdasaryan wrote: > From: Dave Hansen > > The per-VMA locks have been around for several years. They've had some > bugs worked out of them and have seen quite wide use. However, they > are still only available when architectures explicitly enable them. > Remove the conditional compilation around the per-VMA locks, making > them available on all architectures and configs. > > The approach up to now seemed to be to add ARCH_SUPPORTS_PER_VMA_LOCK > when the architecture started using per-VMA locks in the fault > handler. But, contrary to the naming, the Kconfig option does not > really indicate whether the architecture supports per-VMA locks or > not. It is more of a marker for whether the architecture is likely to > benefit from per-VMA locks. > > To me, the most important thing side-effect of universal availability > is letting per-VMA locks be used in SMP=n configs. This lets us use > per-VMA locking in all x86 code without fallbacks. > > Overall, this just generally makes the kernel simpler. Just look at > the diffstat. It also opens the door to users that want to use the > per-VMA locks in common code. Doing *that* brings additional > simplifications. > > The downside of this is adding some fields to vm_area_struct and > mm_struct. There are likely ways to optimize this, especially for > things like SMP=n configs. For now, do the simplest thing: use the > same implementation everywhere. > > == Considerations for NOMMU config == Echoing what I commented on v6 after v7 was already sent (not realizing there was a v7 after my inbox got flooded) Maybe the NOMMU "support" could have been had in a separate prep patch (where a lot of the description below could have been moved), making the patch itself just mostly a removal of code. Acked-by: David Hildenbrand (Arm) -- Cheers, David