From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f197.google.com (mail-qk1-f197.google.com [209.85.222.197]) by kanga.kvack.org (Postfix) with ESMTP id CFAC36B0272 for ; Wed, 14 Nov 2018 04:39:09 -0500 (EST) Received: by mail-qk1-f197.google.com with SMTP id h68so36813564qke.3 for ; Wed, 14 Nov 2018 01:39:09 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id m29si665488qtm.216.2018.11.14.01.39.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Nov 2018 01:39:09 -0800 (PST) Subject: Re: Memory hotplug softlock issue References: <20181114070909.GB2653@MiWiFi-R3L-srv> <5a6c6d6b-ebcd-8bfa-d6e0-4312bfe86586@redhat.com> <20181114090134.GG23419@dhcp22.suse.cz> <4449a0a2-be72-02bb-9f02-ed2484b160f8@redhat.com> <20181114093720.GI23419@dhcp22.suse.cz> From: David Hildenbrand Message-ID: <88b7d3a8-3d51-4516-aaee-ba7397796c36@redhat.com> Date: Wed, 14 Nov 2018 10:39:06 +0100 MIME-Version: 1.0 In-Reply-To: <20181114093720.GI23419@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Baoquan He , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, aarcange@redhat.com >>> Failing on ENOMEM is a questionable thing. I haven't seen that happening >>> wildly but if it is a case then I wouldn't be opposed. >>> >>>> You mentioned memory pressure, if our host is under memory pressure we >>>> can easily trigger running into an endless loop there, because we >>>> basically ignore -ENOMEM e.g. when we cannot get a page to migrate some >>>> memory to be offlined. I assume this is the case here. >>>> do_migrate_range() could be the bad boy if it keeps failing forever and >>>> we keep retrying. >> >> I've seen quite some issues while playing with virtio-mem, but didn't >> have the time to look into the details. Still on my long list of things >> to look into. > > Memory hotplug is really far away from being optimal and robust. This > has always been the case. Issues used to be workaround by retry limits > etc. If we ever want to make it more robust we have to bite a bullet and > actually chase all the issues that might be basically anywhere and fix > them. This is just a nature of a pony that memory hotplug is. > Yes I agree, no more workarounds. -- Thanks, David / dhildenb