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=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 75A8FC433E2 for ; Wed, 16 Sep 2020 07:59:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BB7C2087D for ; Wed, 16 Sep 2020 07:59:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726494AbgIPH7F (ORCPT ); Wed, 16 Sep 2020 03:59:05 -0400 Received: from mx2.suse.de ([195.135.220.15]:48372 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726068AbgIPH7E (ORCPT ); Wed, 16 Sep 2020 03:59:04 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7FC68AFF8; Wed, 16 Sep 2020 07:59:18 +0000 (UTC) Date: Wed, 16 Sep 2020 09:59:00 +0200 From: Michal Hocko To: Vijay Balakrishna Cc: Andrew Morton , "Kirill A. Shutemov" , Oleg Nesterov , Song Liu , Andrea Arcangeli , Pavel Tatashin , Allen Pais , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [v2 2/2] mm: khugepaged: avoid overriding min_free_kbytes set by user Message-ID: <20200916075900.GE18998@dhcp22.suse.cz> References: <1600204258-13683-1-git-send-email-vijayb@linux.microsoft.com> <1600204258-13683-2-git-send-email-vijayb@linux.microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1600204258-13683-2-git-send-email-vijayb@linux.microsoft.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 15-09-20 14:10:58, Vijay Balakrishna wrote: > set_recommended_min_free_kbytes need to honor min_free_kbytes set by the > user. Post start-of-day THP enable or memory hotplug operations can > lose user specified min_free_kbytes, in particular when it is higher than > calculated recommended value. Also modifying "recommended_min" variable > type to "int" from "unsigned long" to avoid undesired result noticed > during testing. It is due to comparing "unsigned long" with "int" type. > > Signed-off-by: Vijay Balakrishna > Cc: stable@vger.kernel.org > Reviewed-by: Pavel Tatashin > --- > mm/khugepaged.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 4f7107476a6f..b4b753ba411a 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2253,7 +2253,7 @@ static void set_recommended_min_free_kbytes(void) > { > struct zone *zone; > int nr_zones = 0; > - unsigned long recommended_min; > + int recommended_min; > > for_each_populated_zone(zone) { > /* > @@ -2280,12 +2280,12 @@ static void set_recommended_min_free_kbytes(void) > > /* don't ever allow to reserve more than 5% of the lowmem */ > recommended_min = min(recommended_min, > - (unsigned long) nr_free_buffer_pages() / 20); > + (int) nr_free_buffer_pages() / 20); nr_free_buffer_pages can oveflow in int on very large machines. > recommended_min <<= (PAGE_SHIFT-10); > > - if (recommended_min > min_free_kbytes) { > + if (recommended_min > user_min_free_kbytes) { This can decrease the size theoretically. Because user_min_free_kbytes is -1 by default and recommended_min might be <= min_free_kbytes. You need to check both. Also can we make user_min_free_kbytes 0 by default? From a quick look, nobody should really care. > if (user_min_free_kbytes >= 0) > - pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n", > + pr_info("raising min_free_kbytes from %d to %d to help transparent hugepage allocations\n", > min_free_kbytes, recommended_min); > > min_free_kbytes = recommended_min; > -- > 2.28.0 > -- Michal Hocko SUSE Labs