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 75864C43334 for ; Thu, 23 Jun 2022 23:34:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AD45C8E01A2; Thu, 23 Jun 2022 19:34:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A83C48E01A1; Thu, 23 Jun 2022 19:34:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 94C3C8E01A2; Thu, 23 Jun 2022 19:34:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 8357D8E01A1 for ; Thu, 23 Jun 2022 19:34:50 -0400 (EDT) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 528EE7D5 for ; Thu, 23 Jun 2022 23:34:50 +0000 (UTC) X-FDA: 79611107940.08.AC28929 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf01.hostedemail.com (Postfix) with ESMTP id C1FF74001F for ; Thu, 23 Jun 2022 23:34:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1656027289; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=TC9n5LVZ0qtZNHnNNofBIXeuXG+fzZwRilor8n4TIWw=; b=Gqp+76YX+7K4K6o0WrnRY2AHKj/wWBEuWyD+WAV/wJAJ87h6cpNeEyXhSNDoILNtrwp94i dUKu/5IEn7G+bYjCTKVkEnMDwQ5O1/xSqWgC0Z4iblxeVARkuISVAiTxz6+s/uqmIYO6GG TXiF8otEJERZw8VpWb8hgPf8Tpy7B/k= Received: from mail-io1-f72.google.com (mail-io1-f72.google.com [209.85.166.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-649-fEXZ4oM3N3ucn0VsHep3ew-1; Thu, 23 Jun 2022 19:34:47 -0400 X-MC-Unique: fEXZ4oM3N3ucn0VsHep3ew-1 Received: by mail-io1-f72.google.com with SMTP id o11-20020a6bcf0b000000b0067328c4275bso468970ioa.8 for ; Thu, 23 Jun 2022 16:34:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=TC9n5LVZ0qtZNHnNNofBIXeuXG+fzZwRilor8n4TIWw=; b=tnKGKv+FQXWHMIFFME87BlGWM50djzjCRFSDk5j5D7XXCoHJt318qICQomIaYnlNcP N4rDw3Hy2/CYiLJTf6YPDFCU1qEf8vAKAa48glkmiYHlIqT5K+ie9mNqoDO0T6KiuMSm R2RbioBUKf7iaqSTWGAZMNW4EuLaC07AYKWn8t/prI0IzJzdWihGPQt/kcr71LtO1eZe Upy5f0M2BoVX9KmyaXa0ae9nPoAXaAZ2TUPNlubQJILO7CnjUi7fYWkZxqlY6Dhsj46C S93/1tUMjBhe/xr7p5xLTZrFB7Mmixcb9dpu2AyOvzCTz71UzSzvDQ7pEIQTzDMOh0oo /ULA== X-Gm-Message-State: AJIora9AWZK1cHVXDhQOSP4MYmAvGMwwXn1J3OqwGI5IlSYYYlqBa0Hv yI83MP0rwJMclM5gdHye3Z3BRTmiMhRQ9qH9YBRNUQnh1gud08/IesWudRSmdYvg9aYXC3L4j69 gNaaSEeFnZrQ= X-Received: by 2002:a05:6e02:b25:b0:2d8:eef1:ccd1 with SMTP id e5-20020a056e020b2500b002d8eef1ccd1mr6709860ilu.180.1656027287330; Thu, 23 Jun 2022 16:34:47 -0700 (PDT) X-Google-Smtp-Source: AGRyM1tAgXxC1MiXVfW3199e0sm6Tn/Z7ug97f9dcYDw6mLtTmVEFrH10uM8TA5A0e0AGvA80lCbMw== X-Received: by 2002:a05:6e02:b25:b0:2d8:eef1:ccd1 with SMTP id e5-20020a056e020b2500b002d8eef1ccd1mr6709854ilu.180.1656027287096; Thu, 23 Jun 2022 16:34:47 -0700 (PDT) Received: from xz-m1.local (cpec09435e3e0ee-cmc09435e3e0ec.cpe.net.cable.rogers.com. [99.241.198.116]) by smtp.gmail.com with ESMTPSA id n27-20020a02a19b000000b00339dfa082a7sm340427jah.109.2022.06.23.16.34.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jun 2022 16:34:46 -0700 (PDT) Date: Thu, 23 Jun 2022 19:34:44 -0400 From: Peter Xu To: Nadav Amit Cc: linux-mm@kvack.org, Nadav Amit , David Hildenbrand , Mike Kravetz , Hugh Dickins , Andrew Morton , Axel Rasmussen , Mike Rapoport Subject: Re: [PATCH v1 4/5] userfaultfd: zero access/write hints Message-ID: References: <20220622185038.71740-1-namit@vmware.com> <20220622185038.71740-5-namit@vmware.com> MIME-Version: 1.0 In-Reply-To: <20220622185038.71740-5-namit@vmware.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656027289; a=rsa-sha256; cv=none; b=awxff84ezKv0h049IgMgDSLDqf2bjzcr48Jp2cTE1U7c/tzpkO/s2ILl5UsSiGHv/Kjgu6 NZ36UTYJffRPTrm+62vlpnzybfafLerFWZPaZnzUufsUf44m3OwvYmVY67dFQkeMRrGWVE MVBjf90/VKY3N1mRHUvOPTIYAMfvQyE= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Gqp+76YX; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf01.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656027289; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=TC9n5LVZ0qtZNHnNNofBIXeuXG+fzZwRilor8n4TIWw=; b=1SBx3XbU4Ex8tbgZXGMM8Edb75q3vU4VkMPCG1H6x7wGLHH02MUTXz6ki1SB0USLr1aIGF KYy1Pc6hO0OeZm6u5y/Rm8sINAxYPQfL0Uhi77ZJJZqXTR9Si94bqkHYgv/Iks2BJ/4GXC DgvxhqvUx9zAIQpnf7HmM8h1KoiNY/k= X-Stat-Signature: ws6rbp6sm4y3gw1mj6gc1cfdhp41a1jg X-Rspamd-Queue-Id: C1FF74001F Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Gqp+76YX; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf01.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1656027289-771539 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 Wed, Jun 22, 2022 at 11:50:37AM -0700, Nadav Amit wrote: > From: Nadav Amit > > When userfaultfd provides a zeropage in response to ioctl, it provides a > readonly alias to the zero page. If the page is later written (which is > the likely scenario), page-fault occurs and the page-fault allocator > allocates a page and rewires the page-tables. > > This is an expensive flow for cases in which a page is likely be written > to. Users can use the copy ioctl to initialize zero page (by copying > zeros), but this is also wasteful. > > Allow userfaultfd users to efficiently map initialized zero-pages that > are writable. IF UFFDIO_ZEROPAGE_MODE_WRITE_LIKELY is provided would map > a clear page instead of an alias to the zero page. > > For consistency, introduce also UFFDIO_ZEROPAGE_MODE_ACCESS_LIKELY. > > Suggested-by: David Hildenbrand > Cc: Mike Kravetz > Cc: Hugh Dickins > Cc: Andrew Morton > Cc: Axel Rasmussen > Cc: Peter Xu > Cc: Mike Rapoport > Signed-off-by: Nadav Amit Acked-by: Peter Xu -- Peter Xu