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 96912FC1D for ; Wed, 4 Sep 2024 16:01:53 +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=1725465715; cv=none; b=ux56FXJmS+r0S1wIaZG+FqLzFbkiZXqCn5j3g/2ajGzWt5nN+k8nZuvK87gBWK0EakaF155trezz8zFz49dhv5ToT5tsdmMwk9vJzYQbIQouFku59MJcMBbqs0+8ZQk8LrMVbz+CjmIy7Jl/q+jyXWsAmP/wEKrCRQWLKip+4r8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725465715; c=relaxed/simple; bh=lSUMwSmWSwy7rFl69KtEi7NAoauuw1/sm9LSVhNiIL4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZfgHQ7aPpSERDl23HuaMyKDxxx89wCpKJy0dUSvTcJT26yhn3gbX5mIwM4WP/kDxiFnxIIKtqJcL6H0hSUGjg66OLEqLA24M3clVyi2LWNBGSBO51V46b2RoIuby4EaRH9/581BRB2Y7obbz5W8ve54yZU0PUvuqWswLLiE5Nh8= 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 3250FFEC; Wed, 4 Sep 2024 09:02:19 -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 84B9D3F73B; Wed, 4 Sep 2024 09:01:49 -0700 (PDT) Message-ID: <91a2d578-3ff2-41e1-a980-0d78c0663959@arm.com> Date: Wed, 4 Sep 2024 17:01:48 +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> <2427338d-7be5-4939-8d01-6d99b9167fea@arm.com> <98f73b2f-ec1c-4e81-bfb2-6e02ebc4cdae@arm.com> From: Ryan Roberts In-Reply-To: <98f73b2f-ec1c-4e81-bfb2-6e02ebc4cdae@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 04/09/2024 16:41, Dev Jain wrote: > > On 9/4/24 17:06, Ryan Roberts wrote: >> 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. > > Sorry, forgot to mention, it applies on v6.11-rc5. Thanks, I'll give it a review tomorrow. Although I suspect that Andrew will want it based against mm-unstable once it gets into shape for merging. > >> >> Thanks, >> Ryan >>