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[209.132.183.28]) by mx.google.com with ESMTPS id t15si2356018qtn.39.2019.03.13.05.18.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 13 Mar 2019 05:18:06 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 01BDC307CB2E; Wed, 13 Mar 2019 12:18:06 +0000 (UTC) Received: from [10.36.116.141] (ovpn-116-141.ams2.redhat.com [10.36.116.141]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2DC325D706; Wed, 13 Mar 2019 12:17:55 +0000 (UTC) Subject: Re: [RFC][Patch v9 2/6] KVM: Enables the kernel to isolate guest free pages To: Nitesh Narayan Lal , Alexander Duyck Cc: "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> <20190306155048.12868-3-nitesh@redhat.com> <2d9ae889-a9b9-7969-4455-ff36944f388b@redhat.com> <22e4b1cd-38a5-6642-8cbe-d68e4fcbb0b7@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> 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: <8826829a-973d-8117-3fe3-8e33170acfb8@redhat.com> Date: Wed, 13 Mar 2019 13:17:54 +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: <1ae522f1-1e98-9eef-324c-29585fe574d6@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Wed, 13 Mar 2019 12:18:06 +0000 (UTC) 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 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 :) -- Thanks, David / dhildenb