From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E204C433EF for ; Sun, 28 Nov 2021 04:10:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B5DD06B0075; Sat, 27 Nov 2021 23:10:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id AE62C6B0078; Sat, 27 Nov 2021 23:10:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 986596B007B; Sat, 27 Nov 2021 23:10:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0024.hostedemail.com [216.40.44.24]) by kanga.kvack.org (Postfix) with ESMTP id 838166B0075 for ; Sat, 27 Nov 2021 23:10:33 -0500 (EST) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 2AC6C8248D52 for ; Sun, 28 Nov 2021 04:10:23 +0000 (UTC) X-FDA: 78857011884.02.1DE8815 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf07.hostedemail.com (Postfix) with ESMTP id 2230810002C7 for ; Sun, 28 Nov 2021 04:10:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Ck+FaDnoeTtSYbJ567N4WEPz2AxsL6omNDpZ2NQqJFA=; b=afW5+8q9nlh1wdvcDjeYmoeAH1 fX4yvxNZFTCi02bJSjeI8oiW0vCFli14y/9NIQ+2/RhTLh0CH2X1bExtej3GWFeZJpcmwIB5xfNBs IsZ40VmPSkz6EOQPodaMoj2zn7U1trQ9CtkM3NQ6GRUAtr2RXNAOdnoBy9B4Hp8QbAneLilW1Thfj hPQShpvUYTvi0X5mIgooVxCccU5ujOUtAFtZ0Dv8NQYuCWY/2+W3vXVeWT4HPhvw6kcpgRHthenTl GcuOi7GFHR0w9XuUISgaP5Rq0QXLCdYKFUZjEaipkMFQT4zAgUqsMvZjj3jZQjVFSJC0gm3fJIEzQ gejxXqlQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mrBVp-000afT-2n; Sun, 28 Nov 2021 04:10:01 +0000 Date: Sun, 28 Nov 2021 04:10:01 +0000 From: Matthew Wilcox To: Mina Almasry Cc: Jonathan Corbet , David Hildenbrand , "Paul E . McKenney" , Yu Zhao , Andrew Morton , Peter Xu , Ivan Teterevkov , Florian Schmidt , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v7] mm: Add PM_THP_MAPPED to /proc/pid/pagemap Message-ID: References: <20211123000102.4052105-1-almasrymina@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211123000102.4052105-1-almasrymina@google.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 2230810002C7 X-Stat-Signature: 5wxnfkymjmustgk11zs1axx9se5cg9wo Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=afW5+8q9; dmarc=none; spf=none (imf07.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-HE-Tag: 1638072617-741879 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 Mon, Nov 22, 2021 at 04:01:02PM -0800, Mina Almasry wrote: > Add PM_THP_MAPPED MAPPING to allow userspace to detect whether a given virt > address is currently mapped by a transparent huge page or not. Example > use case is a process requesting THPs from the kernel (via a huge tmpfs > mount for example), for a performance critical region of memory. The > userspace may want to query whether the kernel is actually backing this > memory by hugepages or not. But what is userspace going to _do_ differently if the kernel hasn't backed the memory with huge pages?