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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 996A2C433F5 for ; Wed, 13 Oct 2021 07:45:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 43B7D60E96 for ; Wed, 13 Oct 2021 07:45:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 43B7D60E96 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id BE14794000E; Wed, 13 Oct 2021 03:45:08 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B91A2940007; Wed, 13 Oct 2021 03:45:08 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A808694000E; Wed, 13 Oct 2021 03:45:08 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0095.hostedemail.com [216.40.44.95]) by kanga.kvack.org (Postfix) with ESMTP id 98702940007 for ; Wed, 13 Oct 2021 03:45:08 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 4EF0B8249980 for ; Wed, 13 Oct 2021 07:45:08 +0000 (UTC) X-FDA: 78690628296.05.FF3CA92 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf11.hostedemail.com (Postfix) with ESMTP id D2448F0000AF for ; Wed, 13 Oct 2021 07:45:07 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id B9B8A20104; Wed, 13 Oct 2021 07:45:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1634111106; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GHyshz0cICB/AZMDvcehyJPMU7hPdJzLEsFgbHtpGYg=; b=X2BZzerbgTbg/ZEimFKi9jb6HeSQeqLRZpKXAgJsorxCn8uiz4CSj0h5ZDI+wjFs5mcRvx 3g3qU/oUx5W3yKUsgc1YpIS9o85u9nvGVJLur81VE20SvX40OD9l7p7GkY/T9/cmgijJpm pf6KCtqQgdIm7QsbsUxBVvbImwpE4qo= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1634111106; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GHyshz0cICB/AZMDvcehyJPMU7hPdJzLEsFgbHtpGYg=; b=twefKO+XN3LWMnNou1STJ0t3Sgx+QqKq+0wGPdDe+VcHxAnx+DwaAxgbcREPXSYdJ/mHC3 tjQ/dN455C5wNsCw== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id A919513CBE; Wed, 13 Oct 2021 07:45:06 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id UMqnKIKOZmEFfAAAMHmgww (envelope-from ); Wed, 13 Oct 2021 07:45:06 +0000 Message-ID: <5ca9c03f-5d2e-fe7e-8c16-cd3003c962bb@suse.cz> Date: Wed, 13 Oct 2021 09:45:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: Memory Compaction Question Content-Language: en-US To: Daniel Hoffman , linux-mm@kvack.org References: From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D2448F0000AF X-Stat-Signature: twp9ucf1txskzcyd1j64nj8m5sk7hass Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=X2BZzerb; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=twefKO+X; dmarc=none; spf=pass (imf11.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-HE-Tag: 1634111107-581275 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: On 10/12/21 20:35, Daniel Hoffman wrote: > In the Linux Kconfig documentation for memory compaction, you mention > that almost nobody should turn the option off, and if so that you'd > like to hear about why at this email address. > > Has anybody email'd you to explain why they'd need it turned off? I'm I don't personally recall about a mail triggered specifically by this kconfig hint. There have been cases where people complained about high overhead (e.g. CPU usage) which was sometimes due to bugs. A common non-bug reason for high usage has been transparent hugepages (THP). The default settings for THPs today should mean that compaction will not be tried as hard in that context, but many people also learned from various old blogs that they should be disabling THP altogether and keep doing it. > doing R&D in this area and understanding these edge cases (if they > exist) would be great. > > Thanks! > > > Screenshot from 2021-10-12 13-35-03.png >