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b=ULpp5wXvxp8ruE57XvePuaLSKpdR7mxuUjLjxkrt7nNUZoiUjrr2PR0YB9NpSsuIK ONixgaWNK79QglC6EK/DegLv3O4sZdwc5ba0lFt46T0yI2LeoUMMN9GGWXzSOnqiU8 Ll6/fP4rzePhgEcCjIAgGL+hPcVrzqSKDefkSz9mPc4tFXzMDYQ+cI2+VXm1lFsgHJ eJqc4zlSMfKpsqnGVhfS0vKEV2f9aiKHiYK5yOBHcjBHCy6SFT/ARfmkPQaf5vd2Tk 1/ENCyCLUKRQRFB2x/McgPoHxywk+tA3COwfNhOShqfG56WYq6nonqulNdwEmfudVt nDNADHVg4tODg== Message-ID: Date: Thu, 10 Sep 2026 17:20:35 +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 Cc: akpm@linux-foundation.org, 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: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 5AAFCC000D X-Stat-Signature: x33uau9zuba1tjb3nkmbzjugptumm6za X-HE-Tag: 1789053644-55609 X-HE-Meta: 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 LfveyNE+ LnjjIm914t4mXf3jrmFneHnBar/sCIPaAOGhhZ3LrDI9LEujz3aqyxSu1Z4dUEmvHJvjNFDJ8IINTDpJORE6kPpFuek3auCwao3Y7lwNkzjshM7tSqPDqUYRi3tgJNhPVh6OzDRjko9mJHjk5yhOJqxyKaQ6qCkSuNt6zNF8KYcAv4K48ztIc95njzqDhd9ttnoBH1+G/AOITbU0up2BYfA4rT73MuUjqs5TAIyknAa7h1PGsHdFXqnRknaBOPwmrg8xtpS0YNUMTAK4oXEFE9AOf3ev3XagA68EyhQ2nmgLf6ImF6XActi5TTT9SJsUPoFJPerkOKRJSx1ALhBmW+zWCleHE8iZrszVZ7f9wHd5GSn1S+vtK9bGg9mjLt1+04skxcnYqHNq3srY4NT00DH0YjA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/10/26 16:50, Suren Baghdasaryan wrote: > On Thu, Sep 10, 2026 at 3:09 AM David Hildenbrand (Arm) > wrote: >> >> 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. > > Yeah, that would make reviewing indeed easier. I guess current > structure is the result of me adding NOMMU pieces to the pre-existing > patchset. I don't think it's worth refactoring but I can do that if > you insist. I won't insist, it was just commenting because it would cleanly separate the NOMMU oddity from just unlocking it in common code and removing the leftovers :) -- Cheers, David