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[209.132.183.28]) by mx.google.com with ESMTPS id k30si5841591qtc.353.2019.07.12.09.25.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 12 Jul 2019 09:25:54 -0700 (PDT) Received-SPF: pass (google.com: domain of nitesh@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 nitesh@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=nitesh@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com 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 53C38317F31E; Fri, 12 Jul 2019 16:25:53 +0000 (UTC) Received: from [10.40.205.73] (unknown [10.40.205.73]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B14EB1001DF6; Fri, 12 Jul 2019 16:25:20 +0000 (UTC) Subject: Re: [RFC][Patch v11 1/2] mm: page_hinting: core infrastructure To: Alexander Duyck Cc: kvm list , LKML , linux-mm , Paolo Bonzini , lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com, Yang Zhang , Rik van Riel , David Hildenbrand , "Michael S. Tsirkin" , dodgen@google.com, Konrad Rzeszutek Wilk , dhildenb@redhat.com, Andrea Arcangeli , john.starks@microsoft.com, Dave Hansen , Michal Hocko References: <20190710195158.19640-1-nitesh@redhat.com> <20190710195158.19640-2-nitesh@redhat.com> <3c6c6b93-eb21-a04c-d0db-6f1b134540db@redhat.com> <521db934-3acd-5287-6e75-67feead8ca63@redhat.com> From: Nitesh Narayan Lal Openpgp: preference=signencrypt Autocrypt: addr=nitesh@redhat.com; prefer-encrypt=mutual; keydata= mQINBFl4pQoBEADT/nXR2JOfsCjDgYmE2qonSGjkM1g8S6p9UWD+bf7YEAYYYzZsLtbilFTe z4nL4AV6VJmC7dBIlTi3Mj2eymD/2dkKP6UXlliWkq67feVg1KG+4UIp89lFW7v5Y8Muw3Fm uQbFvxyhN8n3tmhRe+ScWsndSBDxYOZgkbCSIfNPdZrHcnOLfA7xMJZeRCjqUpwhIjxQdFA7 n0s0KZ2cHIsemtBM8b2WXSQG9CjqAJHVkDhrBWKThDRF7k80oiJdEQlTEiVhaEDURXq+2XmG jpCnvRQDb28EJSsQlNEAzwzHMeplddfB0vCg9fRk/kOBMDBtGsTvNT9OYUZD+7jaf0gvBvBB lbKmmMMX7uJB+ejY7bnw6ePNrVPErWyfHzR5WYrIFUtgoR3LigKnw5apzc7UIV9G8uiIcZEn C+QJCK43jgnkPcSmwVPztcrkbC84g1K5v2Dxh9amXKLBA1/i+CAY8JWMTepsFohIFMXNLj+B RJoOcR4HGYXZ6CAJa3Glu3mCmYqHTOKwezJTAvmsCLd3W7WxOGF8BbBjVaPjcZfavOvkin0u DaFvhAmrzN6lL0msY17JCZo046z8oAqkyvEflFbC0S1R/POzehKrzQ1RFRD3/YzzlhmIowkM BpTqNBeHEzQAlIhQuyu1ugmQtfsYYq6FPmWMRfFPes/4JUU/PQARAQABtCVOaXRlc2ggTmFy YXlhbiBMYWwgPG5pbGFsQHJlZGhhdC5jb20+iQI9BBMBCAAnBQJZeKUKAhsjBQkJZgGABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheAAAoJEKOGQNwGMqM56lEP/A2KMs/pu0URcVk/kqVwcBhU SnvB8DP3lDWDnmVrAkFEOnPX7GTbactQ41wF/xwjwmEmTzLrMRZpkqz2y9mV0hWHjqoXbOCS 6RwK3ri5e2ThIPoGxFLt6TrMHgCRwm8YuOSJ97o+uohCTN8pmQ86KMUrDNwMqRkeTRW9wWIQ EdDqW44VwelnyPwcmWHBNNb1Kd8j3xKlHtnS45vc6WuoKxYRBTQOwI/5uFpDZtZ1a5kq9Ak/ MOPDDZpd84rqd+IvgMw5z4a5QlkvOTpScD21G3gjmtTEtyfahltyDK/5i8IaQC3YiXJCrqxE r7/4JMZeOYiKpE9iZMtS90t4wBgbVTqAGH1nE/ifZVAUcCtycD0f3egX9CHe45Ad4fsF3edQ ESa5tZAogiA4Hc/yQpnnf43a3aQ67XPOJXxS0Qptzu4vfF9h7kTKYWSrVesOU3QKYbjEAf95 NewF9FhAlYqYrwIwnuAZ8TdXVDYt7Z3z506//sf6zoRwYIDA8RDqFGRuPMXUsoUnf/KKPrtR ceLcSUP/JCNiYbf1/QtW8S6Ca/4qJFXQHp0knqJPGmwuFHsarSdpvZQ9qpxD3FnuPyo64S2N Dfq8TAeifNp2pAmPY2PAHQ3nOmKgMG8Gn5QiORvMUGzSz8Lo31LW58NdBKbh6bci5+t/HE0H pnyVf5xhNC/FuQINBFl4pQoBEACr+MgxWHUP76oNNYjRiNDhaIVtnPRqxiZ9v4H5FPxJy9UD Bqr54rifr1E+K+yYNPt/Po43vVL2cAyfyI/LVLlhiY4yH6T1n+Di/hSkkviCaf13gczuvgz4 KVYLwojU8+naJUsiCJw01MjO3pg9GQ+47HgsnRjCdNmmHiUQqksMIfd8k3reO9SUNlEmDDNB XuSzkHjE5y/R/6p8uXaVpiKPfHoULjNRWaFc3d2JGmxJpBdpYnajoz61m7XJlgwl/B5Ql/6B dHGaX3VHxOZsfRfugwYF9CkrPbyO5PK7yJ5vaiWre7aQ9bmCtXAomvF1q3/qRwZp77k6i9R3 tWfXjZDOQokw0u6d6DYJ0Vkfcwheg2i/Mf/epQl7Pf846G3PgSnyVK6cRwerBl5a68w7xqVU 4KgAh0DePjtDcbcXsKRT9D63cfyfrNE+ea4i0SVik6+N4nAj1HbzWHTk2KIxTsJXypibOKFX 2VykltxutR1sUfZBYMkfU4PogE7NjVEU7KtuCOSAkYzIWrZNEQrxYkxHLJsWruhSYNRsqVBy KvY6JAsq/i5yhVd5JKKU8wIOgSwC9P6mXYRgwPyfg15GZpnw+Fpey4bCDkT5fMOaCcS+vSU1 UaFmC4Ogzpe2BW2DOaPU5Ik99zUFNn6cRmOOXArrryjFlLT5oSOe4IposgWzdwARAQABiQIl BBgBCAAPBQJZeKUKAhsMBQkJZgGAAAoJEKOGQNwGMqM5ELoP/jj9d9gF1Al4+9bngUlYohYu 0sxyZo9IZ7Yb7cHuJzOMqfgoP4tydP4QCuyd9Q2OHHL5AL4VFNb8SvqAxxYSPuDJTI3JZwI7 d8JTPKwpulMSUaJE8ZH9n8A/+sdC3CAD4QafVBcCcbFe1jifHmQRdDrvHV9Es14QVAOTZhnJ vweENyHEIxkpLsyUUDuVypIo6y/Cws+EBCWt27BJi9GH/EOTB0wb+2ghCs/i3h8a+bi+bS7L FCCm/AxIqxRurh2UySn0P/2+2eZvneJ1/uTgfxnjeSlwQJ1BWzMAdAHQO1/lnbyZgEZEtUZJ x9d9ASekTtJjBMKJXAw7GbB2dAA/QmbA+Q+Xuamzm/1imigz6L6sOt2n/X/SSc33w8RJUyor SvAIoG/zU2Y76pKTgbpQqMDmkmNYFMLcAukpvC4ki3Sf086TdMgkjqtnpTkEElMSFJC8npXv 3QnGGOIfFug/qs8z03DLPBz9VYS26jiiN7QIJVpeeEdN/LKnaz5LO+h5kNAyj44qdF2T2AiF HxnZnxO5JNP5uISQH3FjxxGxJkdJ8jKzZV7aT37sC+Rp0o3KNc+GXTR+GSVq87Xfuhx0LRST NK9ZhT0+qkiN7npFLtNtbzwqaqceq3XhafmCiw8xrtzCnlB/C4SiBr/93Ip4kihXJ0EuHSLn VujM7c/b4pps Organization: Red Hat Inc, Message-ID: <89c65447-f876-9aac-957f-85f30ca43b2f@redhat.com> Date: Fri, 12 Jul 2019 12:25:17 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US 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 [10.5.110.41]); Fri, 12 Jul 2019 16:25:53 +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 7/12/19 12:22 PM, Alexander Duyck wrote: > On Thu, Jul 11, 2019 at 6:13 PM Nitesh Narayan Lal wrote: >> >> On 7/11/19 7:20 PM, Alexander Duyck wrote: >>> On Thu, Jul 11, 2019 at 10:58 AM Nitesh Narayan Lal wrote: >>>> On 7/10/19 5:56 PM, Alexander Duyck wrote: >>>>> On Wed, Jul 10, 2019 at 12:52 PM Nitesh Narayan Lal wrote: >>>>>> This patch introduces the core infrastructure for free page hinting in >>>>>> virtual environments. It enables the kernel to track the free pages which >>>>>> can be reported to its hypervisor so that the hypervisor could >>>>>> free and reuse that memory as per its requirement. >>>>>> >>>>>> While the pages are getting processed in the hypervisor (e.g., >>>>>> via MADV_FREE), the guest must not use them, otherwise, data loss >>>>>> would be possible. To avoid such a situation, these pages are >>>>>> temporarily removed from the buddy. The amount of pages removed >>>>>> temporarily from the buddy is governed by the backend(virtio-balloon >>>>>> in our case). >>>>>> >>>>>> To efficiently identify free pages that can to be hinted to the >>>>>> hypervisor, bitmaps in a coarse granularity are used. Only fairly big >>>>>> chunks are reported to the hypervisor - especially, to not break up THP >>>>>> in the hypervisor - "MAX_ORDER - 2" on x86, and to save space. The bits >>>>>> in the bitmap are an indication whether a page *might* be free, not a >>>>>> guarantee. A new hook after buddy merging sets the bits. >>>>>> >>>>>> Bitmaps are stored per zone, protected by the zone lock. A workqueue >>>>>> asynchronously processes the bitmaps, trying to isolate and report pages >>>>>> that are still free. The backend (virtio-balloon) is responsible for >>>>>> reporting these batched pages to the host synchronously. Once reporting/ >>>>>> freeing is complete, isolated pages are returned back to the buddy. >>>>>> >>>>>> There are still various things to look into (e.g., memory hotplug, more >>>>>> efficient locking, possible races when disabling). >>>>>> >>>>>> Signed-off-by: Nitesh Narayan Lal >>> So just FYI, I thought I would try the patches. It looks like there >>> might be a bug somewhere that is causing it to free memory it >>> shouldn't be. After about 10 minutes my VM crashed with a system log >>> full of various NULL pointer dereferences. >> That's interesting, I have tried the patches with MADV_DONTNEED as well. >> I just retried it but didn't see any crash. May I know what kind of >> workload you are running? > I was running the page_fault1 test on a VM with 80G of memory. > >>> The only change I had made >>> is to use MADV_DONTNEED instead of MADV_FREE in QEMU since my headers >>> didn't have MADV_FREE on the host. It occurs to me one advantage of >>> MADV_DONTNEED over MADV_FREE is that you are more likely to catch >>> these sort of errors since it zeros the pages instead of leaving them >>> intact. >> For development purpose maybe. For the final patch-set I think we >> discussed earlier why we should keep MADV_FREE. > I'm still not convinced MADV_FREE is a net win, at least for > performance. You are still paying the cost for the VMEXIT in order to > regain ownership of the page. In the case that you are under memory > pressure it is essentially equivalent to MADV_DONTNEED. Also it > doesn't really do much to help with the memory footprint of the VM > itself. With the MADV_DONTNEED the pages are freed back and you have a > greater liklihood of reducing the overall memory footprint of the > entire system since you would be more likely to be assigned pages that > were recently used rather than having to access a cold page. > > > >>>>>> +void page_hinting_enqueue(struct page *page, int order) >>>>>> +{ >>>>>> + int zone_idx; >>>>>> + >>>>>> + if (!page_hitning_conf || order < PAGE_HINTING_MIN_ORDER) >>>>>> + return; >>>>> I would think it is going to be expensive to be jumping into this >>>>> function for every freed page. You should probably have an inline >>>>> taking care of the order check before you even get here since it would >>>>> be faster that way. >>>> I see, I can take a look. Thanks. >>>>>> + >>>>>> + bm_set_pfn(page); >>>>>> + if (atomic_read(&page_hinting_active)) >>>>>> + return; >>>>> So I would think this piece is racy. Specifically if you set a PFN >>>>> that is somewhere below the PFN you are currently processing in your >>>>> scan it is going to remain unset until you have another page freed >>>>> after the scan is completed. I would worry you can end up with a batch >>>>> free of memory resulting in a group of pages sitting at the start of >>>>> your bitmap unhinted. >>>> True, but that will be hinted next time threshold is met. >>> Yes, but that assumes that there is another free immediately coming. >>> It is possible that you have a big application run and then >>> immediately shut down and have it free all its memory at once. Worst >>> case scenario would be that it starts by freeing from the end and >>> works toward the start. With that you could theoretically end up with >>> a significant chunk of memory waiting some time for another big free >>> to come along. >> Any suggestion on some benchmark/test application which I could run to >> see this kind of behavior? > Like I mentioned before, try doing a VM with a bigger memory > footprint. You could probably just do a stack of VMs like what we were > doing with the memhog test. Basically the longer it takes to process > all the pages the greater the liklihood that there are still pages > left when they are freed. Thanks. Before next posting I will make sure to test with a larger VM (>64GB). -- Thanks Nitesh