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 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 547EBC43381 for ; Wed, 13 Mar 2019 23:19:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1646721019 for ; Wed, 13 Mar 2019 23:19:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727139AbfCMXTF (ORCPT ); Wed, 13 Mar 2019 19:19:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43690 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726183AbfCMXTE (ORCPT ); Wed, 13 Mar 2019 19:19:04 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 27F7E3092650; Wed, 13 Mar 2019 23:19:03 +0000 (UTC) Received: from [10.36.116.76] (ovpn-116-76.ams2.redhat.com [10.36.116.76]) by smtp.corp.redhat.com (Postfix) with ESMTP id 98C60100164A; Wed, 13 Mar 2019 23:18:52 +0000 (UTC) Subject: Re: [RFC][Patch v9 2/6] KVM: Enables the kernel to isolate guest free pages To: Alexander Duyck Cc: Nitesh Narayan Lal , "Michael S. Tsirkin" , kvm list , LKML , linux-mm , Paolo Bonzini , lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com, Yang Zhang , Rik van Riel , dodgen@google.com, Konrad Rzeszutek Wilk , dhildenb@redhat.com, Andrea Arcangeli References: <20190306155048.12868-1-nitesh@redhat.com> <78b604be-2129-a716-a7a6-f5b382c9fb9c@redhat.com> <20190307212845-mutt-send-email-mst@kernel.org> <17d2afa6-556e-ec73-40dc-beac536b3f20@redhat.com> <8f692047-4750-6827-1ee0-d3d354788f09@redhat.com> <41ae8afe-72c9-58e6-0cbb-9375c91ce37a@redhat.com> <1ae522f1-1e98-9eef-324c-29585fe574d6@redhat.com> <8826829a-973d-8117-3fe3-8e33170acfb8@redhat.com> <71d0bd98-ff97-7ed1-1f95-c0d134d0b2a1@redhat.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: <02775cba-3d66-ddbe-f0dd-eb293ad3d7d7@redhat.com> Date: Thu, 14 Mar 2019 00:18:51 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Wed, 13 Mar 2019 23:19:04 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13.03.19 23:54, Alexander Duyck wrote: > On Wed, Mar 13, 2019 at 9:39 AM David Hildenbrand wrote: >> >> On 13.03.19 17:37, Alexander Duyck wrote: >>> On Wed, Mar 13, 2019 at 5:18 AM David Hildenbrand wrote: >>>> >>>> On 13.03.19 12:54, Nitesh Narayan Lal wrote: >>>>> >>>>> On 3/12/19 5:13 PM, Alexander Duyck wrote: >>>>>> On Tue, Mar 12, 2019 at 12:46 PM Nitesh Narayan Lal wrote: >>>>>>> On 3/8/19 4:39 PM, Alexander Duyck wrote: >>>>>>>> On Fri, Mar 8, 2019 at 11:39 AM Nitesh Narayan Lal wrote: >>>>>>>>> On 3/8/19 2:25 PM, Alexander Duyck wrote: >>>>>>>>>> On Fri, Mar 8, 2019 at 11:10 AM Nitesh Narayan Lal wrote: >>>>>>>>>>> On 3/8/19 1:06 PM, Alexander Duyck wrote: >>>>>>>>>>>> On Thu, Mar 7, 2019 at 6:32 PM Michael S. Tsirkin wrote: >>>>>>>>>>>>> On Thu, Mar 07, 2019 at 02:35:53PM -0800, Alexander Duyck wrote: >>>>>>>>>>>>>> The only other thing I still want to try and see if I can do is to add >>>>>>>>>>>>>> a jiffies value to the page private data in the case of the buddy >>>>>>>>>>>>>> pages. >>>>>>>>>>>>> Actually there's one extra thing I think we should do, and that is make >>>>>>>>>>>>> sure we do not leave less than X% off the free memory at a time. >>>>>>>>>>>>> This way chances of triggering an OOM are lower. >>>>>>>>>>>> If nothing else we could probably look at doing a watermark of some >>>>>>>>>>>> sort so we have to have X amount of memory free but not hinted before >>>>>>>>>>>> we will start providing the hints. It would just be a matter of >>>>>>>>>>>> tracking how much memory we have hinted on versus the amount of memory >>>>>>>>>>>> that has been pulled from that pool. >>>>>>>>>>> This is to avoid false OOM in the guest? >>>>>>>>>> Partially, though it would still be possible. Basically it would just >>>>>>>>>> be a way of determining when we have hinted "enough". Basically it >>>>>>>>>> doesn't do us much good to be hinting on free memory if the guest is >>>>>>>>>> already constrained and just going to reallocate the memory shortly >>>>>>>>>> after we hinted on it. The idea is with a watermark we can avoid >>>>>>>>>> hinting until we start having pages that are actually going to stay >>>>>>>>>> free for a while. >>>>>>>>>> >>>>>>>>>>>> It is another reason why we >>>>>>>>>>>> probably want a bit in the buddy pages somewhere to indicate if a page >>>>>>>>>>>> has been hinted or not as we can then use that to determine if we have >>>>>>>>>>>> to account for it in the statistics. >>>>>>>>>>> The one benefit which I can see of having an explicit bit is that it >>>>>>>>>>> will help us to have a single hook away from the hot path within buddy >>>>>>>>>>> merging code (just like your arch_merge_page) and still avoid duplicate >>>>>>>>>>> hints while releasing pages. >>>>>>>>>>> >>>>>>>>>>> I still have to check PG_idle and PG_young which you mentioned but I >>>>>>>>>>> don't think we can reuse any existing bits. >>>>>>>>>> Those are bits that are already there for 64b. I think those exist in >>>>>>>>>> the page extension for 32b systems. If I am not mistaken they are only >>>>>>>>>> used in VMA mapped memory. What I was getting at is that those are the >>>>>>>>>> bits we could think about reusing. >>>>>>>>>> >>>>>>>>>>> If we really want to have something like a watermark, then can't we use >>>>>>>>>>> zone->free_pages before isolating to see how many free pages are there >>>>>>>>>>> and put a threshold on it? (__isolate_free_page() does a similar thing >>>>>>>>>>> but it does that on per request basis). >>>>>>>>>> Right. That is only part of it though since that tells you how many >>>>>>>>>> free pages are there. But how many of those free pages are hinted? >>>>>>>>>> That is the part we would need to track separately and then then >>>>>>>>>> compare to free_pages to determine if we need to start hinting on more >>>>>>>>>> memory or not. >>>>>>>>> Only pages which are isolated will be hinted, and once a page is >>>>>>>>> isolated it will not be counted in the zone free pages. >>>>>>>>> Feel free to correct me if I am wrong. >>>>>>>> You are correct up to here. When we isolate the page it isn't counted >>>>>>>> against the free pages. However after we complete the hint we end up >>>>>>>> taking it out of isolation and returning it to the "free" state, so it >>>>>>>> will be counted against the free pages. >>>>>>>> >>>>>>>>> If I am understanding it correctly you only want to hint the idle pages, >>>>>>>>> is that right? >>>>>>>> Getting back to the ideas from our earlier discussion, we had 3 stages >>>>>>>> for things. Free but not hinted, isolated due to hinting, and free and >>>>>>>> hinted. So what we would need to do is identify the size of the first >>>>>>>> pool that is free and not hinted by knowing the total number of free >>>>>>>> pages, and then subtract the size of the pages that are hinted and >>>>>>>> still free. >>>>>>> To summarize, for now, I think it makes sense to stick with the current >>>>>>> approach as this way we can avoid any locking in the allocation path and >>>>>>> reduce the number of hypercalls for a bunch of MAX_ORDER - 1 page. >>>>>> I'm not sure what you are talking about by "avoid any locking in the >>>>>> allocation path". Are you talking about the spin on idle bit, if so >>>>>> then yes. >>>>> Yeap! >>>>>> However I have been testing your patches and I was correct >>>>>> in the assumption that you forgot to handle the zone lock when you >>>>>> were freeing __free_one_page. >>>>> Yes, these are the steps other than the comments you provided in the >>>>> code. (One of them is to fix release_buddy_page()) >>>>>> I just did a quick copy/paste from your >>>>>> zone lock handling from the guest_free_page_hinting function into the >>>>>> release_buddy_pages function and then I was able to enable multiple >>>>>> CPUs without any issues. >>>>>> >>>>>>> For the next step other than the comments received in the code and what >>>>>>> I mentioned in the cover email, I would like to do the following: >>>>>>> 1. Explore the watermark idea suggested by Alex and bring down memhog >>>>>>> execution time if possible. >>>>>> So there are a few things that are hurting us on the memhog test: >>>>>> 1. The current QEMU patch is only madvising 4K pages at a time, this >>>>>> is disabling THP and hurts the test. >>>>> Makes sense, thanks for pointing this out. >>>>>> >>>>>> 2. The fact that we madvise the pages away makes it so that we have to >>>>>> fault the page back in in order to use it for the memhog test. In >>>>>> order to avoid that penalty we may want to see if we can introduce >>>>>> some sort of "timeout" on the pages so that we are only hinting away >>>>>> old pages that have not been used for some period of time. >>>>> >>>>> Possibly using MADVISE_FREE should also help in this, I will try this as >>>>> well. >>>> >>>> I was asking myself some time ago how MADVISE_FREE will be handled in >>>> case of THP. Please let me know your findings :) >>> >>> The problem with MADVISE_FREE is that it will add additional >>> complication to the QEMU portion of all this as it only applies to >>> anonymous memory if I am not mistaken. >> >> Just as MADV_DONTNEED. So nothing new. Future work. > > I'm pretty sure you can use MADV_DONTNEED to free up file backed > memory, I don't believe this is the case for MADV_FREE, but maybe I am > mistaken. "MADV_DONTNEED cannot be applied to locked pages, Huge TLB pages, or VM_PFNMAP pages." For shmem, hugetlbfs and friends one has to use FALLOC_FL_PUNCH_HOLE as far as I remember (e.g. QEMU postcopy migration has to use it). So effectively, virtio-balloon can as of now only really deal with anonymous memory. And it is the same case for free page hinting. > > On a side note I was just reviewing some stuff related to the reserved > bit and on-lining hotplug memory, and it just occurred to me that most > the PG_offline bit would be a good means to indicate that we hinted > away a page out of the buddy allocator, especially since it is already > used by the balloon drivers anyway. We would just have to add a call > to make sure we clear it when we call __ClearPageBuddy. It looks like > that would currently be in del_page_from_free_area, at least for > linux-next. Hmm, if we only knew who came up with PG_offline ... ;) Unfortunately PG_offline is not a bit, it is mapcount value just like PG_buddy. Well okay, it is a bit in the mapcount value - but as of now, a page can only have one such "page type" at a time as far as I recall. > > I just wanted to get your thoughts on that as it seems like it might > be a good fit. It would be if we could have multiple page types at a time. I haven't had a look yet how realistic that would be. As you correctly noted, balloon drivers use that bit as of now to mark pages that are logically offline (here: "inflated"). > > Thanks. > > - Alex > -- Thanks, David / dhildenb