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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 391ACC433F5 for ; Sun, 6 Mar 2022 09:27:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233086AbiCFJ2H (ORCPT ); Sun, 6 Mar 2022 04:28:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50160 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229614AbiCFJ2F (ORCPT ); Sun, 6 Mar 2022 04:28:05 -0500 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3A3BE434B5; Sun, 6 Mar 2022 01:27:14 -0800 (PST) Received: by verein.lst.de (Postfix, from userid 2407) id 40D9867373; Sun, 6 Mar 2022 10:27:10 +0100 (CET) Date: Sun, 6 Mar 2022 10:27:09 +0100 From: Christoph Hellwig To: Hugh Dickins Cc: Andrew Morton , Mikulas Patocka , Zdenek Kabelac , Lukas Czerner , "Darrick J. Wong" , Miklos Szeredi , Christoph Hellwig , Borislav Petkov , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH mmotm] tmpfs: do not allocate pages on read Message-ID: <20220306092709.GA22883@lst.de> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 04, 2022 at 09:09:01PM -0800, Hugh Dickins wrote: > It's not quite as simple as just removing the test (as Mikulas did): > xfstests generic/013 hung because splice from tmpfs failed on page not > up-to-date and page mapping unset. That can be fixed just by marking > the ZERO_PAGE as Uptodate, which of course it is; doing so here in > shmem_file_read_iter() is distasteful, but seems to be the best way. Shouldn't we set ZERO_PAGE uptodate during early init code as it, uh, is per definition uptodate all the time? > > My intention, though, was to stop using the ZERO_PAGE here altogether: > surely iov_iter_zero() is better for this case? Sadly not: it relies > on clear_user(), and the x86 clear_user() is slower than its copy_user(): > https://lore.kernel.org/lkml/2f5ca5e4-e250-a41c-11fb-a7f4ebc7e1c9@google.com/ Oh, that's sad as just using clear_user would be the right thing to here. > But while we are still using the ZERO_PAGE, let's stop dirtying its > struct page cacheline with unnecessary get_page() and put_page(). > > Reported-by: Mikulas Patocka > Reported-by: Lukas Czerner > Signed-off-by: Hugh Dickins But except for maybe making sure that ZERO_PAGE is always marked uptodate this does looks good to me.