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 6559AECAAD2 for ; Fri, 26 Aug 2022 10:19:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9772C940008; Fri, 26 Aug 2022 06:19:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 926A7940007; Fri, 26 Aug 2022 06:19:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7EE59940008; Fri, 26 Aug 2022 06:19:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 6D776940007 for ; Fri, 26 Aug 2022 06:19:03 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 3312C1C67A2 for ; Fri, 26 Aug 2022 10:19:03 +0000 (UTC) X-FDA: 79841345766.23.04C9E8E Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf22.hostedemail.com (Postfix) with ESMTP id B5628C0015 for ; Fri, 26 Aug 2022 10:19:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1661509141; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iK1Tn6jPwinpVDnV9ak81Ascm2YVGGH4jX+q/msRheo=; b=NL853I4dFQLMddLGXe+dSTgMpqS8ZJgeByEJzebiA3cC3DQJCKCQtGQTmsuphkikuZro4D a/CUdtZyQZuEnRKUMYi0WRimKXCfgtdggEkY3Y+WpsEusKwm1qsbcRgfdTz32/4cxXY5hM UGeiGbEraRKFvVkrigCi/yGLKT1RWYk= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-170-xnDHLoXoMjCd2kD9kXiL4A-1; Fri, 26 Aug 2022 06:19:00 -0400 X-MC-Unique: xnDHLoXoMjCd2kD9kXiL4A-1 Received: by mail-wm1-f70.google.com with SMTP id h82-20020a1c2155000000b003a64d0510d9so759556wmh.8 for ; Fri, 26 Aug 2022 03:19:00 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:organization:from:references :cc:to:content-language:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc; bh=iK1Tn6jPwinpVDnV9ak81Ascm2YVGGH4jX+q/msRheo=; b=uMBxf3R9HbkvczQGPRFqG4asO3eBpWVUuH9Iqml3YaA/c7Q7mY4p+lRXbLzo9v9HMC 8Zr5mLWGKb3a+wWsj3DO8rD83UPzavVt+67ijHQPisdAxEJtoInvzO+WYtdU0wa1C9Qf mI0Pz9ppb52m3RJ7+KkPJaAXgn2o0nJ39LyEmJIE7oo4tdx4TvhewTcXkj62Y/Yq67+E HxrCigln66tKna9TpTE/wih9oyjvm00M1/m95lP/dZuXFi5u+CeT8ge+bDEVD6mTrCj2 2H4JTn6BUCMP8ApLXAaOipXvd7JS9R5AJKx1dwKo8K4IwGacXqlKMLz0Q01Dstt72G4R eU7Q== X-Gm-Message-State: ACgBeo1//Asq+rJiAiJsZ2omyv8dW2mUWijeswyY6Gx2sXy1/vClLU+L HXjbPqaekJ0Y4Fi7os2deGAFL1Q+D7/jE0eEXdVI/tbzhsEDNpRiDepO5DTFLUhO7AMHhTI3fz2 TJqSb3oqf+Qo= X-Received: by 2002:a05:600c:22cd:b0:3a6:7b62:3778 with SMTP id 13-20020a05600c22cd00b003a67b623778mr4870162wmg.45.1661509139725; Fri, 26 Aug 2022 03:18:59 -0700 (PDT) X-Google-Smtp-Source: AA6agR598X1MmjZ3DMV6g3DPym5yBDmE9ppM3iBECP72+NJ+flYXxutjFWYoIdUKJH+PhdkHPCiBew== X-Received: by 2002:a05:600c:22cd:b0:3a6:7b62:3778 with SMTP id 13-20020a05600c22cd00b003a67b623778mr4870141wmg.45.1661509139380; Fri, 26 Aug 2022 03:18:59 -0700 (PDT) Received: from ?IPV6:2003:cb:c708:f600:abad:360:c840:33fa? (p200300cbc708f600abad0360c84033fa.dip0.t-ipconnect.de. [2003:cb:c708:f600:abad:360:c840:33fa]) by smtp.gmail.com with ESMTPSA id b3-20020a5d4d83000000b0020fff0ea0a3sm1457815wru.116.2022.08.26.03.18.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 26 Aug 2022 03:18:58 -0700 (PDT) Message-ID: Date: Fri, 26 Aug 2022 12:18:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [RFC 2/3] mm: changes to split_huge_page() to free zero filled tail pages To: alexlzhu@fb.com, linux-mm@kvack.org Cc: willy@infradead.org, hannes@cmpxchg.org, akpm@linux-foundation.org, riel@surriel.com, kernel-team@fb.com, linux-kernel@vger.kernel.org References: <490fcdd204ae129a2e43614a569a1cf4bdde9196.1661461643.git.alexlzhu@fb.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <490fcdd204ae129a2e43614a569a1cf4bdde9196.1661461643.git.alexlzhu@fb.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1661509142; a=rsa-sha256; cv=none; b=xM2LOCG/9oLhPt+EnB0wM9QYTTDKozLKW+DQavWyUHJFpr8vvG3fsRgSMmfKyr51vMg/ex DvrEWJzhni3BQZN06chx5haAQ+0BmmMyH0INSe0QS0BA8uL+Zh1zDV0BgiHrmFqamE/o8r SV9Db1964gGj+1u9baCL2XsNqL8XBCw= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=NL853I4d; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf22.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1661509142; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=iK1Tn6jPwinpVDnV9ak81Ascm2YVGGH4jX+q/msRheo=; b=nMTKpTP+KEJGpa7VQHPRBt8Tw/95Lz5rVQ+OPXqmhqnvjpWDsLl0k8al+OnIq4469oQRN8 UDLhttBrqwGG4ZHABtJoZwOgG0xqvOnrniVd5NZbxPmimgVgXcdkQU0ztQSsEMdERD3BVh QS8jXHJCfnF07tR125tsYJwijCKDJcA= X-Stat-Signature: 68njjbr3rjzaqtthocoqu5bsxb1pzd1e X-Rspamd-Queue-Id: B5628C0015 X-Rspam-User: X-Rspamd-Server: rspam11 Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=NL853I4d; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf22.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com X-HE-Tag: 1661509142-38977 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 25.08.22 23:30, alexlzhu@fb.com wrote: > From: Alexander Zhu > > Currently, when /sys/kernel/mm/transparent_hugepage/enabled=always is set > there are a large number of transparent hugepages that are almost entirely > zero filled. This is mentioned in a number of previous patchsets > including: > https://lore.kernel.org/all/20210731063938.1391602-1-yuzhao@google.com/ > https://lore.kernel.org/all/ > 1635422215-99394-1-git-send-email-ningzhang@linux.alibaba.com/ > > Currently, split_huge_page() does not have a way to identify zero filled > pages within the THP. Thus these zero pages get remapped and continue to > create memory waste. In this patch, we identify and free tail pages that > are zero filled in split_huge_page(). In this way, we avoid mapping these > pages back into page table entries and can free up unused memory within > THPs. This is based off the previously mentioned patchset by Yu Zhao. > However, we chose to free zero tail pages whenever they are encountered > instead of only on reclaim or migration. We also add a self test to verify > the RssAnon value to make sure zero pages are not remapped. > Isn't this to some degree splitting the THP (PMDs->PTEs + dissolve compound page) and then letting KSM replace the zero-filled page by the shared zeropage? -- Thanks, David / dhildenb