From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AF16D4A9D7C; Thu, 10 Sep 2026 15:20:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789053657; cv=none; b=fifRwbXy+bxUb0ixt1ucJufkcFhCao7ccKcBD0fbBtxLra22pYZRjm3yP5W7N5WcE423p3tcI3OKEaVI9+MkyNfb+8pInmcrUFSlgXlk08Q1I9hFQXiiO5sKi54IsBhqj0N7S4KgfLY9flDsoDRKVrzr4xv4xrOxctg+KCGWFG0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789053657; c=relaxed/simple; bh=NGIFxa6EXjaPvFidFRyX0j4paBV7XR55cWxr2v+K/2g=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IiMB7yJeC5EbaSelFI60+B0VwQ5dkKP96F0EY2E8xBCi60zsvSIuJ8PDUelMiLe+EpNcfB0oJISe4B9d5bBFu3ivrvrwCQ4M1rRvftuIG0gNZ4ye23bejD+DsxLk+B4iRr40P1xL5DLZ3WbxHNArlkuCBRzd5qZY3rdVCM4iNLI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ULpp5wXv; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ULpp5wXv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 58C2D1F0089A; Thu, 10 Sep 2026 15:20:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789053643; bh=X8HbD8dWhuAegusLFvJUvIIHTzWI/tlvAmsxEnzmne8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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