From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 4015C1CFED1 for ; Wed, 4 Sep 2024 11:36:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725449778; cv=none; b=EbiTuXj/mh7Ig15muwKpPH0KoveqG3Dt2tnaswQLjS27XMv51SG1RJM0hNeRCjMu/BFofS4syV3JxxKV86p2eGWC+LuC6MS4AA4Y/Gw+uTBM5T79wGF4CMUflYcq7DOOe6p9jqVvOW4eM97AXRz8HEfarp/9PU1OHJ2F/pf7AX4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725449778; c=relaxed/simple; bh=Nw8g76EL4r6bizMdrVPp/Mh3RpOZ8i0WUsJVrcvq5ck=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uhE4jLrsQ0RSawubWczZDn0orTqOsY0pAAfw580upy2mA6vygb33uK//ZRonO8xv1hy4tBQqd1JkQKAAgZ7JWUFU7XDKykqTohpFWmfcq98IUBuAntJ0HP516kW4QXjHlMHc6XG+hj6/reP0Vn49f7GKpYkg6yTkkSv6RYwYUkM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BBAEBFEC; Wed, 4 Sep 2024 04:36:41 -0700 (PDT) Received: from [10.57.87.65] (unknown [10.57.87.65]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 421993F73F; Wed, 4 Sep 2024 04:36:12 -0700 (PDT) Message-ID: <2427338d-7be5-4939-8d01-6d99b9167fea@arm.com> Date: Wed, 4 Sep 2024 12:36:10 +0100 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 v2 0/2] Do not shatter hugezeropage on wp-fault Content-Language: en-GB To: Dev Jain , akpm@linux-foundation.org, david@redhat.com, willy@infradead.org, kirill.shutemov@linux.intel.com Cc: anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, mark.rutland@arm.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, jglisse@google.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240904100923.290042-1-dev.jain@arm.com> From: Ryan Roberts In-Reply-To: <20240904100923.290042-1-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Dev, On 04/09/2024 11:09, Dev Jain wrote: > It was observed at [1] and [2] that the current kernel behaviour of > shattering a hugezeropage is inconsistent and suboptimal. For a VMA with > a THP allowable order, when we write-fault on it, the kernel installs a > PMD-mapped THP. On the other hand, if we first get a read fault, we get > a PMD pointing to the hugezeropage; subsequent write will trigger a > write-protection fault, shattering the hugezeropage into one writable > page, and all the other PTEs write-protected. The conclusion being, as > compared to the case of a single write-fault, applications have to suffer > 512 extra page faults if they were to use the VMA as such, plus we get > the overhead of khugepaged trying to replace that area with a THP anyway. > > Instead, replace the hugezeropage with a THP on wp-fault. > > v1->v2: > - Wrap do_huge_zero_wp_pmd_locked() around lock and unlock > - Call thp_fault_alloc() before do_huge_zero_wp_pmd_locked() to avoid > - calling sleeping function from spinlock context > > [1]: https://lore.kernel.org/all/3743d7e1-0b79-4eaf-82d5-d1ca29fe347d@arm.com/ > [2]: https://lore.kernel.org/all/1cfae0c0-96a2-4308-9c62-f7a640520242@arm.com/ > > Dev Jain (2): > mm: Abstract THP allocation > mm: Allocate THP on hugezeropage wp-fault > > include/linux/huge_mm.h | 6 ++ > mm/huge_memory.c | 171 +++++++++++++++++++++++++++++----------- > mm/memory.c | 5 +- > 3 files changed, 136 insertions(+), 46 deletions(-) > What is the base for this? It doesn't apply on top of mm-unstable. Thanks, Ryan