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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 DCC6EC28CF6 for ; Wed, 1 Aug 2018 11:08:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 93F5F2083D for ; Wed, 1 Aug 2018 11:08:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 93F5F2083D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388298AbeHAMxY (ORCPT ); Wed, 1 Aug 2018 08:53:24 -0400 Received: from mga05.intel.com ([192.55.52.43]:16904 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387592AbeHAMxY (ORCPT ); Wed, 1 Aug 2018 08:53:24 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 01 Aug 2018 04:08:10 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,431,1526367600"; d="scan'208";a="71677732" Received: from unknown (HELO [10.239.13.97]) ([10.239.13.97]) by orsmga003.jf.intel.com with ESMTP; 01 Aug 2018 04:08:04 -0700 Message-ID: <5B619599.1000307@intel.com> Date: Wed, 01 Aug 2018 19:12:25 +0800 From: Wei Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Michal Hocko CC: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, mst@redhat.com, akpm@linux-foundation.org Subject: Re: [PATCH v2 2/2] virtio_balloon: replace oom notifier with shrinker References: <1532683495-31974-1-git-send-email-wei.w.wang@intel.com> <1532683495-31974-3-git-send-email-wei.w.wang@intel.com> <20180730090041.GC24267@dhcp22.suse.cz> In-Reply-To: <20180730090041.GC24267@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/30/2018 05:00 PM, Michal Hocko wrote: > On Fri 27-07-18 17:24:55, Wei Wang wrote: >> The OOM notifier is getting deprecated to use for the reasons mentioned >> here by Michal Hocko: https://lkml.org/lkml/2018/7/12/314 >> >> This patch replaces the virtio-balloon oom notifier with a shrinker >> to release balloon pages on memory pressure. > It would be great to document the replacement. This is not a small > change... OK. I plan to document the following to the commit log: The OOM notifier is getting deprecated to use for the reasons: - As a callout from the oom context, it is too subtle and easy to generate bugs and corner cases which are hard to track; - It is called too late (after the reclaiming has been performed). Drivers with large amuont of reclaimable memory is expected to be released them at an early age of memory pressure; - The notifier callback isn't aware of the oom contrains; Link: https://lkml.org/lkml/2018/7/12/314 This patch replaces the virtio-balloon oom notifier with a shrinker to release balloon pages on memory pressure. Users can set the amount of memory pages to release each time a shrinker_scan is called via the module parameter balloon_pages_to_shrink, and the default amount is 256 pages. Historically, the feature VIRTIO_BALLOON_F_DEFLATE_ON_OOM has been used to release balloon pages on OOM. We continue to use this feature bit for the shrinker, so the shrinker is only registered when this feature bit has been negotiated with host. In addition, the bug in the replaced virtballoon_oom_notify that only VIRTIO_BALLOON_ARRAY_PFNS_MAX (i.e 256) balloon pages can be freed though the user has specified more than that number is fixed in the shrinker_scan function. Best, Wei