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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45841C433E0 for ; Thu, 18 Jun 2020 00:58:02 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 066BD21924 for ; Thu, 18 Jun 2020 00:58:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ellerman.id.au header.i=@ellerman.id.au header.b="NHTZlTX/" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 066BD21924 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7FC5A6B0006; Wed, 17 Jun 2020 20:58:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7ABF56B0007; Wed, 17 Jun 2020 20:58:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6C0476B000C; Wed, 17 Jun 2020 20:58:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0121.hostedemail.com [216.40.44.121]) by kanga.kvack.org (Postfix) with ESMTP id 55B466B0006 for ; Wed, 17 Jun 2020 20:58:01 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id E90A93576 for ; Thu, 18 Jun 2020 00:58:00 +0000 (UTC) X-FDA: 76940520720.26.class61_061544726e0c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin26.hostedemail.com (Postfix) with ESMTP id BD5B31804B363 for ; Thu, 18 Jun 2020 00:58:00 +0000 (UTC) X-HE-Tag: class61_061544726e0c X-Filterd-Recvd-Size: 3416 Received: from ozlabs.org (ozlabs.org [203.11.71.1]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Thu, 18 Jun 2020 00:57:59 +0000 (UTC) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 49nNpC6gn1z9sSc; Thu, 18 Jun 2020 10:57:55 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1592441876; bh=6zbfkIJEcTCwhluvkJvBqEMwTUGHoNtvQJF2+Rj1LaM=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=NHTZlTX/5g6rn40qsPCUdD6fSYs3H/O96lPB5Od0iDL+byhDWHWQIQLE27MzX0zhE 9gsbQEXMgI1UPVY4mdvDy4wx0BLwEFro2ntSpgtfXzlbJHxHhgyLf98H4FhbaT8dY5 T91UAEm4lqMTVsgNKXUL0DxccrN73ibptXw5UT1d41o6J5a9E8Z3t7whaBu9ZvCQ4s 5Fc//tbxV8gTmwVK6YMSylhlNXJT4WpKvPERA/V1PRuNcd3MzmBiYkdJdjpJ0qgybm I3vWexaORUZkpPuXQ/95I8XjjaSBfuKhGXTJ2Ixrv/l/P0xbKvBR/VShg2ea7diDVv Li/WBRKe9KZ6Q== From: Michael Ellerman To: Peter Zijlstra Cc: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Will Deacon , Andrew Morton , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org Subject: Re: [PATCH 3/3] powerpc/8xx: Provide ptep_get() with 16k pages In-Reply-To: <20200617143826.GJ2531@hirez.programming.kicks-ass.net> References: <341688399c1b102756046d19ea6ce39db1ae4742.1592225558.git.christophe.leroy@csgroup.eu> <20200615132244.GR2531@hirez.programming.kicks-ass.net> <87wo45db8d.fsf@mpe.ellerman.id.au> <20200617143826.GJ2531@hirez.programming.kicks-ass.net> Date: Thu, 18 Jun 2020 10:58:26 +1000 Message-ID: <87pn9xchql.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: BD5B31804B363 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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: Peter Zijlstra writes: > On Thu, Jun 18, 2020 at 12:21:22AM +1000, Michael Ellerman wrote: >> Peter Zijlstra writes: >> > On Mon, Jun 15, 2020 at 12:57:59PM +0000, Christophe Leroy wrote: > >> >> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES) >> >> +#define __HAVE_ARCH_PTEP_GET >> >> +static inline pte_t ptep_get(pte_t *ptep) >> >> +{ >> >> + pte_t pte = {READ_ONCE(ptep->pte), 0, 0, 0}; >> >> + >> >> + return pte; >> >> +} >> >> +#endif >> > >> > Would it make sense to have a comment with this magic? The casual reader >> > might wonder WTH just happened when he stumbles on this :-) >> >> I tried writing a helpful comment but it's too late for my brain to form >> sensible sentences. >> >> Christophe can you send a follow-up with a comment explaining it? In >> particular the zero entries stand out, it's kind of subtle that those >> entries are only populated with the right value when we write to the >> page table. > > static inline pte_t ptep_get(pte_t *ptep) > { > unsigned long val = READ_ONCE(ptep->pte); > /* 16K pages have 4 identical value 4K entries */ > pte_t pte = {val, val, val, val); > return pte; > } > > Maybe something like that? I think val wants to be pte_basic_t, but otherwise yeah I like that much better. cheers