From patchwork Thu Dec 5 23:19:06 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniil Tatianin X-Patchwork-Id: 13896089 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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 107CEE77170 for ; Thu, 5 Dec 2024 23:20:52 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tJL8O-000566-In; Thu, 05 Dec 2024 18:19:48 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tJL8M-00055f-CU for qemu-devel@nongnu.org; Thu, 05 Dec 2024 18:19:46 -0500 Received: from forwardcorp1a.mail.yandex.net ([2a02:6b8:c0e:500:1:45:d181:df01]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tJL8I-0000Wb-RM for qemu-devel@nongnu.org; Thu, 05 Dec 2024 18:19:46 -0500 Received: from mail-nwsmtp-smtp-corp-main-62.myt.yp-c.yandex.net (mail-nwsmtp-smtp-corp-main-62.myt.yp-c.yandex.net [IPv6:2a02:6b8:c12:44a0:0:640:8777:0]) by forwardcorp1a.mail.yandex.net (Yandex) with ESMTPS id D607B60A98; Fri, 6 Dec 2024 02:19:34 +0300 (MSK) Received: from d-tatianin-lin.yandex-team.ru (unknown [2a02:6b8:b081:19::1:8]) by mail-nwsmtp-smtp-corp-main-62.myt.yp-c.yandex.net (smtpcorp/Yandex) with ESMTPSA id UJrB130IfiE0-NncImZyA; Fri, 06 Dec 2024 02:19:34 +0300 X-Yandex-Fwd: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1733440774; bh=JUoFTttEF3Deo7ER7IKccgih/eqluYY8jvvlagW8rA4=; h=Message-Id:Date:Cc:Subject:To:From; b=RUYZq7MkkSpDKc0uq83E21jYGHO9q0OOi+lySrnMSydcpJUvvc0zKwkpGETW2F6zW amlwePFuA0JD7xTiXhOLaryM2bEKjEqU6gvhxA3+jj49qkyYol6iFTsJhfnTq7nyjU bt1uW08J0oQx3mTU75GQXx8jMB+40vNwirxDS7l8= Authentication-Results: mail-nwsmtp-smtp-corp-main-62.myt.yp-c.yandex.net; dkim=pass header.i=@yandex-team.ru From: Daniil Tatianin To: Paolo Bonzini Cc: Daniil Tatianin , Stefan Weil , Peter Xu , Fabiano Rosas , qemu-devel@nongnu.org Subject: [PATCH 0/2] overcommit: introduce mem-lock-onfault Date: Fri, 6 Dec 2024 02:19:06 +0300 Message-Id: <20241205231909.1161950-1-d-tatianin@yandex-team.ru> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Received-SPF: pass client-ip=2a02:6b8:c0e:500:1:45:d181:df01; envelope-from=d-tatianin@yandex-team.ru; helo=forwardcorp1a.mail.yandex.net X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Currently, passing mem-lock=on to QEMU causes memory usage to grow by huge amounts: no memlock: $ qemu-system-x86_64 -overcommit mem-lock=off $ ps -p $(pidof ./qemu-system-x86_64) -o rss= 45652 $ ./qemu-system-x86_64 -overcommit mem-lock=off -enable-kvm $ ps -p $(pidof ./qemu-system-x86_64) -o rss= 39756 memlock: $ qemu-system-x86_64 -overcommit mem-lock=on $ ps -p $(pidof ./qemu-system-x86_64) -o rss= 1309876 $ ./qemu-system-x86_64 -overcommit mem-lock=on -enable-kvm $ ps -p $(pidof ./qemu-system-x86_64) -o rss= 259956 This is caused by the fact that mlockall(2) automatically write-faults every existing and future anonymous mappings in the process right away. One of the reasons to enable mem-lock is to protect a QEMU process' pages from being compacted and migrated by kcompactd (which does so by messing with a live process page tables causing thousands of TLB flush IPIs per second) basically stealing all guest time while it's active. mem-lock=on helps against this (given compact_unevictable_allowed is 0), but the memory overhead it introduces is an undesirable side effect, which we can completely avoid by passing MCL_ONFAULT to mlockall, which is what this series allows to do with a new command line option called mem-lock-onfault. memlock-onfault: $ qemu-system-x86_64 -overcommit mem-lock-onfault=on $ ps -p $(pidof ./qemu-system-x86_64) -o rss= 54004 $ ./qemu-system-x86_64 -overcommit mem-lock-onfault=on -enable-kvm $ ps -p $(pidof ./qemu-system-x86_64) -o rss= 47772 You may notice the memory usage is still slightly higher, in this case by a few megabytes over the mem-lock=off case. I was able to trace this down to a bug in the linux kernel with MCL_ONFAULT not being honored for the early process heap (with brk(2) etc.) so it is still write-faulted in this case, but it's still way less than it was with just the mem-lock=on. Daniil Tatianin (2): os: add an ability to lock memory on_fault overcommit: introduce mem-lock-onfault include/sysemu/os-posix.h | 2 +- include/sysemu/os-win32.h | 3 ++- include/sysemu/sysemu.h | 1 + migration/postcopy-ram.c | 4 ++-- os-posix.c | 10 ++++++++-- qemu-options.hx | 13 ++++++++++--- system/globals.c | 1 + system/vl.c | 18 ++++++++++++++++-- 8 files changed, 41 insertions(+), 11 deletions(-) Reviewed-by: Vladimir Sementsov-Ogievskiy