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 31573ECAAD3 for ; Wed, 7 Sep 2022 23:34:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 51F426B0072; Wed, 7 Sep 2022 19:34:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4A7676B0073; Wed, 7 Sep 2022 19:34:11 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3480E8D0001; Wed, 7 Sep 2022 19:34:11 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 2252C6B0072 for ; Wed, 7 Sep 2022 19:34:11 -0400 (EDT) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id E36CE41964 for ; Wed, 7 Sep 2022 23:34:10 +0000 (UTC) X-FDA: 79886895060.02.A63AFE0 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf24.hostedemail.com (Postfix) with ESMTP id 89BFB18009E for ; Wed, 7 Sep 2022 23:34:10 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 8AC0861AAD; Wed, 7 Sep 2022 23:34:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3D909C433C1; Wed, 7 Sep 2022 23:34:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1662593649; bh=8qHDzjTjq+FV8EUAuXd3KU8y3Cmqs9z+Bxt12Z9Z744=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=d02IjSQKwvtfFUmR3Ty8Hi4MJJl/YGPwkLLtpaOgir0yCYPur1O/yfTODk6eNem9o /msKMYI5LkuTE1TEBYGwBoG8AIycwX/8AQKZ6qtKWUeQWOFT6XRNmmWEP12FyBa2CE HQJu/WZjHcFXa9RuJwfabXtL7FxUkTphYQzazPFA= Date: Wed, 7 Sep 2022 16:34:08 -0700 From: Andrew Morton To: Chen Wandun Cc: , , Subject: Re: [PATCH] mm: avoid unnecessary page table walk for __get_user_pages Message-Id: <20220907163408.f9a9152314d33afc74cb1f0c@linux-foundation.org> In-Reply-To: <20220906024401.133336-1-chenwandun@huawei.com> References: <20220906024401.133336-1-chenwandun@huawei.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662593650; 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=hbVTIqOx1SYcarNCX5O7/PcCj0Uqo07eLKw28kKOyNk=; b=4YjFWXBxxMPsXNiWlCvYih4WtDsvDTjdNgrUBJKXcknjB+0SWRyFyT2jK5YEWSiLjd3MGZ JpOMs+9YT44dYiDpfahLtSsSOAv2ZmxX+CeAMq0xLgmZiUqOHMfRe+8TDRIUNOZ868slnX gqAo9ftpmwPOZYuiQE3ssERtX/pPFGE= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=d02IjSQK; dmarc=none; spf=pass (imf24.hostedemail.com: domain of akpm@linux-foundation.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662593650; a=rsa-sha256; cv=none; b=QKmshkf034KI1QLBgAm8vqx0Skut3iSy25TpoPczEP6dmy130zlCerxdLF/YUnp58hvAiW Ra3p7/Ix0ZoNCXSqPjvQ2koJAUtzbFhRuiWIfrDwDS0o+uGkgeZhRd3E+7mtsyBzoX5d34 mrhmdjTthZH8lp45ril9T+E+08Wa4/M= X-Stat-Signature: iudndcytonfgkhzgbtrasyurqsfz5toy X-Rspamd-Queue-Id: 89BFB18009E Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=d02IjSQK; dmarc=none; spf=pass (imf24.hostedemail.com: domain of akpm@linux-foundation.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1662593650-790571 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 Tue, 6 Sep 2022 10:44:01 +0800 Chen Wandun wrote: > It is no need to walk page table and find pages if faultin_page success > and __get_user_pages does't care pages at all, so directly handle next > page. > > ... > > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1198,7 +1198,10 @@ static long __get_user_pages(struct mm_struct *mm, > PTR_ERR(page) == -EMLINK, locked); > switch (ret) { > case 0: > - goto retry; > + if (pages) > + goto retry; > + else > + goto next_page; > case -EBUSY: > case -EAGAIN: > ret = 0; Looks right to me. I redid the changelog somewhat: : There is no need to walk page tables and find pages if faultin_page)_ : succeeds and __get_user_pages)_ doesn't care about populating the pages[] : array. So directly go on to handle the next page.