From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vk0-f69.google.com (mail-vk0-f69.google.com [209.85.213.69]) by kanga.kvack.org (Postfix) with ESMTP id AFD156B2B51 for ; Thu, 23 Aug 2018 13:56:42 -0400 (EDT) Received: by mail-vk0-f69.google.com with SMTP id m71-v6so2458215vke.3 for ; Thu, 23 Aug 2018 10:56:42 -0700 (PDT) Received: from userp2120.oracle.com (userp2120.oracle.com. [156.151.31.85]) by mx.google.com with ESMTPS id i189-v6si953559vkc.178.2018.08.23.10.56.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 Aug 2018 10:56:41 -0700 (PDT) Subject: Re: [PATCH v3 1/2] mm: migration: fix migration of huge PMD shared pages From: Mike Kravetz References: <20180821205902.21223-2-mike.kravetz@oracle.com> <201808220831.eM0je51n%fengguang.wu@intel.com> <975b740d-26a6-eb3f-c8ca-1a9995d0d343@oracle.com> <20180823124855.GI29735@dhcp22.suse.cz> <12ea5339-f2b1-62b4-6d37-57d737fac34a@oracle.com> Message-ID: Date: Thu, 23 Aug 2018 10:56:30 -0700 MIME-Version: 1.0 In-Reply-To: <12ea5339-f2b1-62b4-6d37-57d737fac34a@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: kbuild test robot , kbuild-all@01.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A . Shutemov" , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Vlastimil Babka , Naoya Horiguchi , Davidlohr Bueso , Andrew Morton , stable@vger.kernel.org On 08/23/2018 10:01 AM, Mike Kravetz wrote: > On 08/23/2018 05:48 AM, Michal Hocko wrote: >> On Tue 21-08-18 18:10:42, Mike Kravetz wrote: >> [...] >> >> OK, after burning myself when trying to be clever here it seems like >> your proposed solution is indeed simpler. >> >>> +bool huge_pmd_sharing_possible(struct vm_area_struct *vma, >>> + unsigned long *start, unsigned long *end) >>> +{ >>> + unsigned long check_addr = *start; >>> + bool ret = false; >>> + >>> + if (!(vma->vm_flags & VM_MAYSHARE)) >>> + return ret; >>> + >>> + for (check_addr = *start; check_addr < *end; check_addr += PUD_SIZE) { >>> + unsigned long a_start = check_addr & PUD_MASK; >>> + unsigned long a_end = a_start + PUD_SIZE; >> >> I guess this should be rather in HPAGE_SIZE * PTRS_PER_PTE units as >> huge_pmd_unshare does. > > Sure, I can do that. On second thought, this is more similar to vma_shareable() which uses PUD_MASK and PUD_SIZE. In fact Kirill asked me to put in a common helper for this and vma_shareable. So, I would prefer to leave it as PUD* unless you feel strongly. IMO, it would make more sense to change this in huge_pmd_unshare as PMD sharing is pretty explicitly tied to PUD_SIZE. But, that is a future cleanup. -- Mike Kravetz