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Mon, 21 Jun 2021 12:36:52 +0000 Received: from nvdebian.localnet (172.20.187.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Mon, 21 Jun 2021 12:36:48 +0000 From: Alistair Popple To: Peter Xu CC: , , Andrea Arcangeli , "Kirill A . Shutemov" , Axel Rasmussen , Nadav Amit , Hugh Dickins , Jerome Glisse , Jason Gunthorpe , Andrew Morton , Miaohe Lin , Mike Rapoport , Matthew Wilcox , Mike Kravetz Subject: Re: [PATCH v3 09/27] mm: Introduce ZAP_FLAG_SKIP_SWAP Date: Mon, 21 Jun 2021 22:36:46 +1000 Message-ID: <5565576.ugXqPVlkE4@nvdebian> In-Reply-To: <20210527202135.30890-1-peterx@redhat.com> References: <20210527201927.29586-1-peterx@redhat.com> <20210527202135.30890-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Originating-IP: [172.20.187.5] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: dfc79bb5-b41c-4d7f-0d3e-08d934b13f91 X-MS-TrafficTypeDiagnostic: MN2PR12MB4655: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.112.34;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:schybrid03.nvidia.com;CAT:NONE;SFS:(4636009)(376002)(39860400002)(136003)(396003)(346002)(36840700001)(46966006)(316002)(36906005)(356005)(82310400003)(36860700001)(5660300002)(426003)(478600001)(7636003)(6916009)(9576002)(7416002)(54906003)(9686003)(186003)(8936002)(83380400001)(82740400003)(16526019)(86362001)(8676002)(33716001)(47076005)(2906002)(70206006)(26005)(70586007)(4326008)(336012)(39026012);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Jun 2021 12:36:52.8203 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: dfc79bb5-b41c-4d7f-0d3e-08d934b13f91 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT041.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4655 Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=gEqCYSuq; spf=none (imf02.hostedemail.com: domain of apopple@nvidia.com has no SPF policy when checking 40.107.244.68) smtp.mailfrom=apopple@nvidia.com; dmarc=pass (policy=none) header.from=nvidia.com X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 693EC42110A3 X-Stat-Signature: jywrdtxk389aux796brn1fe9xdw8ttoe X-HE-Tag: 1624279015-767618 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Friday, 28 May 2021 6:21:35 AM AEST Peter Xu wrote: > Firstly, the comment in zap_pte_range() is misleading because it checks against > details rather than check_mappings, so it's against what the code did. > > Meanwhile, it's confusing too on not explaining why passing in the details > pointer would mean to skip all swap entries. New user of zap_details could > very possibly miss this fact if they don't read deep until zap_pte_range() > because there's no comment at zap_details talking about it at all, so swap > entries could be errornously skipped without being noticed. > > This partly reverts 3e8715fdc03e ("mm: drop zap_details::check_swap_entries"), > but introduce ZAP_FLAG_SKIP_SWAP flag, which means the opposite of previous > "details" parameter: the caller should explicitly set this to skip swap > entries, otherwise swap entries will always be considered (which is still the > major case here). > > Cc: Kirill A. Shutemov > Signed-off-by: Peter Xu > --- > include/linux/mm.h | 12 ++++++++++++ > mm/memory.c | 8 +++++--- > 2 files changed, 17 insertions(+), 3 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 52d3ef2ed753..1adf313a01fe 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1723,6 +1723,8 @@ extern void user_shm_unlock(size_t, struct user_struct *); > > /* Whether to check page->mapping when zapping */ > #define ZAP_FLAG_CHECK_MAPPING BIT(0) > +/* Whether to skip zapping swap entries */ > +#define ZAP_FLAG_SKIP_SWAP BIT(1) > > /* > * Parameter block passed down to zap_pte_range in exceptional cases. > @@ -1745,6 +1747,16 @@ zap_check_mapping_skip(struct zap_details *details, struct page *page) > return details->zap_mapping != page_rmapping(page); > } > > +/* Return true if skip swap entries, false otherwise */ > +static inline bool > +zap_skip_swap(struct zap_details *details) Minor nit-pick but imho it would be nice if the naming was consistent between this and check mapping. Ie. zap_skip_swap()/zap_skip_check_mapping() or zap_swap_skip()/zap_check_mapping_skip(). > +{ > + if (!details) > + return false; > + > + return details->zap_flags & ZAP_FLAG_SKIP_SWAP; > +} > + > struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, > pte_t pte); > struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, > diff --git a/mm/memory.c b/mm/memory.c > index c9dc4e9e05b5..8a3751be87ba 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1376,8 +1376,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, > continue; > } > > - /* If details->check_mapping, we leave swap entries. */ > - if (unlikely(details)) > + if (unlikely(zap_skip_swap(details))) > continue; > > if (!non_swap_entry(entry)) > @@ -3328,7 +3327,10 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start, > pgoff_t nr, bool even_cows) > { > pgoff_t first_index = start, last_index = start + nr - 1; > - struct zap_details details = { .zap_mapping = mapping }; > + struct zap_details details = { > + .zap_mapping = mapping, I meant to comment on this in the previous patch, but it might be nice to set .zap_mapping in the !even_cows case below to make it very obvious it only applies to ZAP_FLAG_CHECK_MAPPING. Otherwise I think this is a good clean up which makes things clearer. I double checked that unmap_mapping_pages() was the only place in the existing code that needs ZAP_FLAG_SKIP_SWAP and that appears to be the case so there shouldn't be any behaviour changes from this. Reviewed-by: Alistair Popple > + .zap_flags = ZAP_FLAG_SKIP_SWAP, > + }; > > if (!even_cows) > details.zap_flags |= ZAP_FLAG_CHECK_MAPPING; >