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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 BA022C742A1 for ; Fri, 12 Jul 2019 01:13:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7F5C021019 for ; Fri, 12 Jul 2019 01:13:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729094AbfGLBNH convert rfc822-to-8bit (ORCPT ); Thu, 11 Jul 2019 21:13:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53062 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726199AbfGLBNG (ORCPT ); Thu, 11 Jul 2019 21:13:06 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CD29C307D92F; Fri, 12 Jul 2019 01:13:05 +0000 (UTC) Received: from [10.40.204.17] (ovpn-204-17.brq.redhat.com [10.40.204.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 115605C207; Fri, 12 Jul 2019 01:12:49 +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> 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: <521db934-3acd-5287-6e75-67feead8ca63@redhat.com> Date: Thu, 11 Jul 2019 21:12:45 -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: 8BIT Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Fri, 12 Jul 2019 01:13:06 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > 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. > >>>> --- >>>> include/linux/page_hinting.h | 45 +++++++ >>>> mm/Kconfig | 6 + >>>> mm/Makefile | 1 + >>>> mm/page_alloc.c | 18 +-- >>>> mm/page_hinting.c | 250 +++++++++++++++++++++++++++++++++++ >>>> 5 files changed, 312 insertions(+), 8 deletions(-) >>>> create mode 100644 include/linux/page_hinting.h >>>> create mode 100644 mm/page_hinting.c >>>> >>>> diff --git a/include/linux/page_hinting.h b/include/linux/page_hinting.h >>>> new file mode 100644 >>>> index 000000000000..4900feb796f9 >>>> --- /dev/null >>>> +++ b/include/linux/page_hinting.h >>>> @@ -0,0 +1,45 @@ >>>> +/* SPDX-License-Identifier: GPL-2.0 */ >>>> +#ifndef _LINUX_PAGE_HINTING_H >>>> +#define _LINUX_PAGE_HINTING_H >>>> + >>>> +/* >>>> + * Minimum page order required for a page to be hinted to the host. >>>> + */ >>>> +#define PAGE_HINTING_MIN_ORDER (MAX_ORDER - 2) >>>> + >>> Why use (MAX_ORDER - 2)? Is this just because of the issues I pointed >>> out earlier for is it due to something else? I'm just wondering if >>> this will have an impact on architectures outside of x86 as I had >>> chose pageblock_order which happened to be MAX_ORDER - 2 on x86, but I >>> don't know that the impact of doing that is on other architectures >>> versus the (MAX_ORDER - 2) approach you took here. >> If I am not wrong then any order < (MAX_ORDER - 2) will break the THP. >> That's one reason we decided to stick with this. > That is true for x86, but I don't think that is true for other > architectures. That is why I went with pageblock_order instead of just > using a fixed value such as MAX_ORDER - 2. I see, I will have to check this. > > > >>>> diff --git a/mm/page_hinting.c b/mm/page_hinting.c >>>> new file mode 100644 >>>> index 000000000000..0bfa09f8c3ed >>>> --- /dev/null >>>> +++ b/mm/page_hinting.c >>>> @@ -0,0 +1,250 @@ >>>> +// SPDX-License-Identifier: GPL-2.0 >>>> +/* >>>> + * Page hinting core infrastructure to enable a VM to report free pages to its >>>> + * hypervisor. >>>> + * >>>> + * Copyright Red Hat, Inc. 2019 >>>> + * >>>> + * Author(s): Nitesh Narayan Lal >>>> + */ >>>> + >>>> +#include >>>> +#include >>>> +#include >>>> +#include >>>> + >>>> +/* >>>> + * struct zone_free_area: For a single zone across NUMA nodes, it holds the >>>> + * bitmap pointer to track the free pages and other required parameters >>>> + * used to recover these pages by scanning the bitmap. >>>> + * @bitmap: Pointer to the bitmap in PAGE_HINTING_MIN_ORDER >>>> + * granularity. >>>> + * @base_pfn: Starting PFN value for the zone whose bitmap is stored. >>>> + * @end_pfn: Indicates the last PFN value for the zone. >>>> + * @free_pages: Tracks the number of free pages of granularity >>>> + * PAGE_HINTING_MIN_ORDER. >>>> + * @nbits: Indicates the total size of the bitmap in bits allocated >>>> + * at the time of initialization. >>>> + */ >>>> +struct zone_free_area { >>>> + unsigned long *bitmap; >>>> + unsigned long base_pfn; >>>> + unsigned long end_pfn; >>>> + atomic_t free_pages; >>>> + unsigned long nbits; >>>> +} free_area[MAX_NR_ZONES]; >>>> + >>> You still haven't addressed the NUMA issue I pointed out with v10. You >>> are only able to address the first set of zones with this setup. As >>> such you can end up missing large sections of memory if it is split >>> over multiple nodes. >> I think I did. > I just realized what you did. Actually this doesn't really improve > things in my opinion. More comments below. > >>>> +static void init_hinting_wq(struct work_struct *work); >>>> +static DEFINE_MUTEX(page_hinting_init); >>>> +const struct page_hinting_config *page_hitning_conf; >>>> +struct work_struct hinting_work; >>>> +atomic_t page_hinting_active; >>>> + >>>> +void free_area_cleanup(int nr_zones) >>>> +{ >>> I'm not sure why you are passing nr_zones as an argument here. Won't >>> this always be MAX_NR_ZONES? >> free_area_cleanup() gets called from page_hinting_disable() and >> page_hinting_enable(). In page_hinting_enable() when the allocation >> fails we may not have to perform cleanup for all the zones everytime. > Just adding a NULL pointer check to this loop below would still keep > it pretty cheap as the cost for initializing memory to 0 isn't that > high, and this is slow path anyway. Either way I guess it works. Yeah. > You > might want to reset the bitmap pointer to NULL though after you free > it to more easily catch the double free case. I think resetting the bitmap pointer to NULL is a good idea. Thanks. > >>>> + int zone_idx; >>>> + >>>> + for (zone_idx = 0; zone_idx < nr_zones; zone_idx++) { >>>> + bitmap_free(free_area[zone_idx].bitmap); >>>> + free_area[zone_idx].base_pfn = 0; >>>> + free_area[zone_idx].end_pfn = 0; >>>> + free_area[zone_idx].nbits = 0; >>>> + atomic_set(&free_area[zone_idx].free_pages, 0); >>>> + } >>>> +} >>>> + >>>> +int page_hinting_enable(const struct page_hinting_config *conf) >>>> +{ >>>> + unsigned long bitmap_size = 0; >>>> + int zone_idx = 0, ret = -EBUSY; >>>> + struct zone *zone; >>>> + >>>> + mutex_lock(&page_hinting_init); >>>> + if (!page_hitning_conf) { >>>> + for_each_populated_zone(zone) { >>> So for_each_populated_zone will go through all of the NUMA nodes. So >>> if I am not mistaken you will overwrite the free_area values of all >>> the previous nodes with the last node in the system. >> Not sure if I understood. > I misread the code. More comments below. > >>> So if we have a >>> setup that has all the memory in the first node, and none in the >>> second it would effectively disable free page hinting would it not? >> Why will it happen? The base_pfn will still be pointing to the base_pfn >> of the first node. Isn't? > So this does address my concern however, it introduces a new issue. > Specifically you could end up introducing a gap of unused bits if the > memory from one zone is not immediately adjacent to another. This gets > back to the SPARSEMEM issue that I think Dave pointed out. Yeah, he did point it out. It looks a valid issue, I will look into it. > > > > >>>> +static void scan_zone_free_area(int zone_idx, int free_pages) >>>> +{ >>>> + int ret = 0, order, isolated_cnt = 0; >>>> + unsigned long set_bit, start = 0; >>>> + LIST_HEAD(isolated_pages); >>>> + struct page *page; >>>> + struct zone *zone; >>>> + >>>> + for (;;) { >>>> + ret = 0; >>>> + set_bit = find_next_bit(free_area[zone_idx].bitmap, >>>> + free_area[zone_idx].nbits, start); >>>> + if (set_bit >= free_area[zone_idx].nbits) >>>> + break; >>>> + page = pfn_to_online_page((set_bit << PAGE_HINTING_MIN_ORDER) + >>>> + free_area[zone_idx].base_pfn); >>>> + if (!page) >>>> + continue; >>>> + zone = page_zone(page); >>>> + spin_lock(&zone->lock); >>>> + >>>> + if (PageBuddy(page) && page_private(page) >= >>>> + PAGE_HINTING_MIN_ORDER) { >>>> + order = page_private(page); >>>> + ret = __isolate_free_page(page, order); >>>> + } >>>> + clear_bit(set_bit, free_area[zone_idx].bitmap); >>>> + atomic_dec(&free_area[zone_idx].free_pages); >>>> + spin_unlock(&zone->lock); >>>> + if (ret) { >>>> + /* >>>> + * restoring page order to use it while releasing >>>> + * the pages back to the buddy. >>>> + */ >>>> + set_page_private(page, order); >>>> + list_add_tail(&page->lru, &isolated_pages); >>>> + isolated_cnt++; >>>> + if (isolated_cnt == page_hitning_conf->max_pages) { >>>> + page_hitning_conf->hint_pages(&isolated_pages); >>>> + release_buddy_pages(&isolated_pages); >>>> + isolated_cnt = 0; >>>> + } >>>> + } >>>> + start = set_bit + 1; >>>> + } >>>> + if (isolated_cnt) { >>>> + page_hitning_conf->hint_pages(&isolated_pages); >>>> + release_buddy_pages(&isolated_pages); >>>> + } >>>> +} >>>> + >>> I really worry that this loop is going to become more expensive as the >>> size of memory increases. For example if we hint on just 16 pages we >>> would have to walk something like 4K bits, 512 longs, if a system had >>> 64G of memory. Have you considered testing with a larger memory >>> footprint to see if it has an impact on performance? >> I am hoping this will be noticeable in will-it-scale's page_fault1, if I >> run it on a larger system? > What you will probably see is that the CPU that is running the scan is > going to be sitting at somewhere near 100% because I cannot see how it > can hope to stay efficient if it has to check something like 512 64b > longs searching for just a handful of idle pages. > >>>> +static void init_hinting_wq(struct work_struct *work) >>>> +{ >>>> + int zone_idx, free_pages; >>>> + >>>> + atomic_set(&page_hinting_active, 1); >>>> + for (zone_idx = 0; zone_idx < MAX_NR_ZONES; zone_idx++) { >>>> + free_pages = atomic_read(&free_area[zone_idx].free_pages); >>>> + if (free_pages >= page_hitning_conf->max_pages) >>>> + scan_zone_free_area(zone_idx, free_pages); >>>> + } >>>> + atomic_set(&page_hinting_active, 0); >>>> +} >>>> + >>>> +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? -- Thanks Nitesh