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 12C9FFC1D for ; Wed, 4 Sep 2024 15:42:09 +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=1725464531; cv=none; b=CtlVeJ2ihaKL+8AQenTkPA+zS2Zb/hizzx6HwBv4FFxx6aDnj5tmVaqT0NmHE+0RQ0+dZb+hluz9RESs8vQ7otp7HqDoE2GsyozomgSAMROU7iwcFl6bzglJhco13/epNh6J2im/j8+R4QCinSS6NtGa2HAazGQhhu++QPdjXyw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725464531; c=relaxed/simple; bh=WXqVMEPhAqQEHeHg6JMAVBSWvqNx5vVJjEp/4AaHW6U=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IiSnn1iQkzBPE97EWZ2zjPhOsB1UCp6dmju1d08x6enArNY8xt4Ak9/9zaCxA44f33XZeyzS/KKDFSAQbXNo4MN3gOzDiFl6TPjnoPYoEP7xR6fxTrKNh7Vu+BOzWX7mi9fBJMnZEmyQ2P7vLEHVlyg7ITuOTCTVQXwpHzgKMMQ= 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 7865BFEC; Wed, 4 Sep 2024 08:42:35 -0700 (PDT) Received: from [10.163.62.239] (unknown [10.163.62.239]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 72F283F73F; Wed, 4 Sep 2024 08:42:00 -0700 (PDT) Message-ID: <98f73b2f-ec1c-4e81-bfb2-6e02ebc4cdae@arm.com> Date: Wed, 4 Sep 2024 21:11:57 +0530 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 To: Ryan Roberts , 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> Content-Language: en-US From: Dev Jain In-Reply-To: <2427338d-7be5-4939-8d01-6d99b9167fea@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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, > Ryan >