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 7C185C7618E for ; Fri, 21 Apr 2023 12:37:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231875AbjDUMhZ (ORCPT ); Fri, 21 Apr 2023 08:37:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229464AbjDUMhX (ORCPT ); Fri, 21 Apr 2023 08:37:23 -0400 Received: from outbound-smtp52.blacknight.com (outbound-smtp52.blacknight.com [46.22.136.236]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 877B4193 for ; Fri, 21 Apr 2023 05:37:22 -0700 (PDT) Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp52.blacknight.com (Postfix) with ESMTPS id F1603FACC5 for ; Fri, 21 Apr 2023 13:37:20 +0100 (IST) Received: (qmail 23836 invoked from network); 21 Apr 2023 12:37:20 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.21.103]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 21 Apr 2023 12:37:20 -0000 Date: Fri, 21 Apr 2023 13:37:19 +0100 From: Mel Gorman To: Johannes Weiner Cc: linux-mm@kvack.org, Kaiyang Zhao , Vlastimil Babka , David Rientjes , linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [RFC PATCH 03/26] mm: make pageblock_order 2M per default Message-ID: <20230421123719.w7tufd6asqdpxcf3@techsingularity.net> References: <20230418191313.268131-1-hannes@cmpxchg.org> <20230418191313.268131-4-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20230418191313.268131-4-hannes@cmpxchg.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 18, 2023 at 03:12:50PM -0400, Johannes Weiner wrote: > pageblock_order can be of various sizes, depending on configuration, > but the default is MAX_ORDER-1. Given 4k pages, that comes out to > 4M. This is a large chunk for the allocator/reclaim/compaction to try > to keep grouped per migratetype. It's also unnecessary as the majority > of higher order allocations - THP and slab - are smaller than that. > > Before subsequent patches increase the effort that goes into > maintaining migratetype isolation, it's important to first set the > defrag block size to what's likely to have common consumers. > > Signed-off-by: Johannes Weiner This patch may be a distraction in the context of this series. I don't feel particularly strongly about it but it has strong bikeshed potential. For configurations that support huge pages of any sort, it should be PMD_ORDER, for anything else the choice is arbitrary. 2M is as good a guess as anyway because even if it was tied to the PAGE_ALLOC_COSTLY_ORDER then the pageblock bitmap overhead might be annoying. -- Mel Gorman SUSE Labs