Received: by 2002:a05:6a10:a0d1:0:0:0:0 with SMTP id j17csp3294566pxa; Tue, 25 Aug 2020 17:44:26 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwPhvVnK459rXyEgKuBmnYqmKrUvys5l2fGkd4ZY8/zHt2EFZ1ZUsF5/XH+JZvWYzNr6yLU X-Received: by 2002:a17:906:158a:: with SMTP id k10mr383000ejd.174.1598402666188; Tue, 25 Aug 2020 17:44:26 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1598402666; cv=none; d=google.com; s=arc-20160816; b=dTcHXZ8gYCC5ymD0I+1O0pVe6AUGo8uYcS93iVM0juSJWtzPPkDxiR7uE3sAhJrdug K9DJR3FutXcdhKwFZx4yS66rXtPg4r8rOHfEgA87iB574hqFOfP7ZQnwGsM4aNyfp9oP J2xApyL0tNqrvIhSkD6kbJ2NHbLU58Uz7vleNlQyikaarIuQGG8ozWzQWIPcBjbqmKMW WFXN2niUkddC5/D8NCp2fEpEa3f5trFZhtwPGf/4WQATXcsV684VnzMw86i98no7SbTq gRpHCqsydLOa7CRX+8OjVN7htQ1w1dV1JeDCeQx61HGznWmmmVNuN5S8JwugYRWaNfhR PoFA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:content-transfer-encoding:mime-version :references:in-reply-to:message-id:subject:cc:to:from:date :dkim-signature; bh=0AcEc2eAmS3fJiebPk/8JJZClMNhA0VjiBzgKf/t+Kk=; b=ktwGZujlls+7rXfqObJoyToGUPj3A5yn7qsqW5bIEzSgOBa5UYjacLRE9OD9KUWq6m NEZZ1C+5X0IMgEhw3BqYtAdRS6/widpq/YxbNQ0DM7HJmfU0kusFXslwSM50GJ520iSo AQoGh+Y/UvKEWEY8xjVyB5uPNH6sAs4AGM57R/w9JwVewbaCZkW9+sEt8RSg/jW8v0q/ n2RGtTeWeIz4NY9nnwbhZoFacKNC+XDr3+e6did5/3S3dO8RjJPB3tf3QOuDi1rHAK2h z8TVorNnhsQTuJa1ddcMWewGACbxCOjEZyq1ZSzivEeYU/artp3bffG5jIsn4E46Kt9j 6aPw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=OxYZSN59; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id k20si451112eje.105.2020.08.25.17.44.02; Tue, 25 Aug 2020 17:44:26 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=OxYZSN59; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726716AbgHZAm7 (ORCPT + 99 others); Tue, 25 Aug 2020 20:42:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:57022 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726541AbgHZAm6 (ORCPT ); Tue, 25 Aug 2020 20:42:58 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0049A2074A; Wed, 26 Aug 2020 00:42:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598402578; bh=GQlLj22PHNu4N2tC0wyjXvzJ8I9QqXfye6YxJQk0AoI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=OxYZSN59BtoftXpHxY2VztXYGvH7IvTYtN7mbBPS/DtafZaujOxpL7Tk5uQSKIuc3 gZsUpzoMJhC3HvsUMPwoZu3veTLFPErcRXGX3asPMRUK22zZEx/lPNQfrklr/ek5Fr bax8IkLeW5HbCKNyrxIK+QndxGbWYdXHimqKbgqo= Date: Tue, 25 Aug 2020 17:42:57 -0700 From: Andrew Morton To: Joonsoo Kim Cc: Linux Memory Management List , LKML , Michal Hocko , Vlastimil Babka , "Aneesh Kumar K . V" , kernel-team@lge.com, Joonsoo Kim Subject: Re: [PATCH for v5.9] mm/page_alloc: handle a missing case for memalloc_nocma_{save/restore} APIs Message-Id: <20200825174257.5b48a5dd24b5e08a915b101e@linux-foundation.org> In-Reply-To: References: <1598331582-19923-1-git-send-email-iamjoonsoo.kim@lge.com> <20200824221049.edb3c540bbfc859a6806600d@linux-foundation.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 25 Aug 2020 14:34:32 +0900 Joonsoo Kim wrote: > > > > That's a bunch more code on a very hot path to serve an obscure feature > > which has a single obscure callsite. > > > > Can we instead put the burden on that callsite rather than upon > > everyone? For (dumb) example, teach __gup_longterm_locked() to put the > > page back if it's CMA and go get another one? > > Hmm... Unfortunately, it cannot ensure that we eventually get the non-CMA page. > I think that the only way to ensure it is to implement the > functionality here. We can > use 'unlikely' or 'static branch' to reduce the overhead for a really > rare case but > for now I have no idea how to completely remove the overhead. Gee, there must be something? Provide the gup code with a special entry point which takes the page straight from __rmqueue() and bypasses the pcp lists?