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=unavailable 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 5097AC742A0 for ; Thu, 11 Jul 2019 17:59:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1497320872 for ; Thu, 11 Jul 2019 17:59:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728863AbfGKR66 convert rfc822-to-8bit (ORCPT ); Thu, 11 Jul 2019 13:58:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49754 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728451AbfGKR65 (ORCPT ); Thu, 11 Jul 2019 13:58:57 -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 E53EC4ACDF; Thu, 11 Jul 2019 17:58:56 +0000 (UTC) Received: from [10.18.17.163] (dhcp-17-163.bos.redhat.com [10.18.17.163]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 399A01001B10; Thu, 11 Jul 2019 17:58:48 +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> 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: <3c6c6b93-eb21-a04c-d0db-6f1b134540db@redhat.com> Date: Thu, 11 Jul 2019 13:58:47 -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 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 11 Jul 2019 17:58:57 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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 >> --- >> 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. > >> +/* >> + * struct page_hinting_config: holds the information supplied by the balloon >> + * device to page hinting. >> + * @hint_pages: Callback which reports the isolated pages >> + * synchornously to the host. >> + * @max_pages: Maxmimum pages that are going to be hinted to the host >> + * at a time of granularity >= PAGE_HINTING_MIN_ORDER. >> + */ >> +struct page_hinting_config { >> + void (*hint_pages)(struct list_head *list); >> + int max_pages; >> +}; >> + >> +extern int __isolate_free_page(struct page *page, unsigned int order); >> +extern void __free_one_page(struct page *page, unsigned long pfn, >> + struct zone *zone, unsigned int order, >> + int migratetype, bool hint); >> +#ifdef CONFIG_PAGE_HINTING >> +void page_hinting_enqueue(struct page *page, int order); >> +int page_hinting_enable(const struct page_hinting_config *conf); >> +void page_hinting_disable(void); >> +#else >> +static inline void page_hinting_enqueue(struct page *page, int order) >> +{ >> +} >> + >> +static inline int page_hinting_enable(const struct page_hinting_config *conf) >> +{ >> + return -EOPNOTSUPP; >> +} >> + >> +static inline void page_hinting_disable(void) >> +{ >> +} >> +#endif >> +#endif /* _LINUX_PAGE_HINTING_H */ >> diff --git a/mm/Kconfig b/mm/Kconfig >> index f0c76ba47695..e97fab429d9b 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -765,4 +765,10 @@ config GUP_BENCHMARK >> config ARCH_HAS_PTE_SPECIAL >> bool >> >> +# PAGE_HINTING will allow the guest to report the free pages to the >> +# host in fixed chunks as soon as the threshold is reached. >> +config PAGE_HINTING >> + bool >> + def_bool n >> + depends on X86_64 >> endmenu > If there are no issue with using the term "PAGE_HINTING" I guess I > will update my patch set to use that term instead of aeration. Not sure, at places like virtio_balloon, we may have to think of something else to avoid any confusion. > >> diff --git a/mm/Makefile b/mm/Makefile >> index ac5e5ba78874..73be49177656 100644 >> --- a/mm/Makefile >> +++ b/mm/Makefile >> @@ -94,6 +94,7 @@ obj-$(CONFIG_Z3FOLD) += z3fold.o >> obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o >> obj-$(CONFIG_CMA) += cma.o >> obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o >> +obj-$(CONFIG_PAGE_HINTING) += page_hinting.o >> obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o >> obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o >> obj-$(CONFIG_USERFAULTFD) += userfaultfd.o >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index d66bc8abe0af..8a44338bd04e 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -69,6 +69,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include >> @@ -874,10 +875,10 @@ compaction_capture(struct capture_control *capc, struct page *page, >> * -- nyc >> */ >> >> -static inline void __free_one_page(struct page *page, >> +inline void __free_one_page(struct page *page, >> unsigned long pfn, >> struct zone *zone, unsigned int order, >> - int migratetype) >> + int migratetype, bool hint) >> { >> unsigned long combined_pfn; >> unsigned long uninitialized_var(buddy_pfn); >> @@ -980,7 +981,8 @@ static inline void __free_one_page(struct page *page, >> migratetype); >> else >> add_to_free_area(page, &zone->free_area[order], migratetype); >> - >> + if (hint) >> + page_hinting_enqueue(page, order); >> } > I'm not sure I am a fan of the way the word "hint" is used here. At > first I thought this was supposed to be !hint since I thought hint > meant that it was a hinted page, not that we need to record that this > page has been freed. Maybe "record" or "report" might be a better word > to use here. "hint" basically means that the page is supposed to be hinted. >> /* >> @@ -1263,7 +1265,7 @@ static void free_pcppages_bulk(struct zone *zone, int count, >> if (unlikely(isolated_pageblocks)) >> mt = get_pageblock_migratetype(page); >> >> - __free_one_page(page, page_to_pfn(page), zone, 0, mt); >> + __free_one_page(page, page_to_pfn(page), zone, 0, mt, true); >> trace_mm_page_pcpu_drain(page, 0, mt); >> } >> spin_unlock(&zone->lock); >> @@ -1272,14 +1274,14 @@ static void free_pcppages_bulk(struct zone *zone, int count, >> static void free_one_page(struct zone *zone, >> struct page *page, unsigned long pfn, >> unsigned int order, >> - int migratetype) >> + int migratetype, bool hint) >> { >> spin_lock(&zone->lock); >> if (unlikely(has_isolate_pageblock(zone) || >> is_migrate_isolate(migratetype))) { >> migratetype = get_pfnblock_migratetype(page, pfn); >> } >> - __free_one_page(page, pfn, zone, order, migratetype); >> + __free_one_page(page, pfn, zone, order, migratetype, hint); >> spin_unlock(&zone->lock); >> } >> >> @@ -1369,7 +1371,7 @@ static void __free_pages_ok(struct page *page, unsigned int order) >> migratetype = get_pfnblock_migratetype(page, pfn); >> local_irq_save(flags); >> __count_vm_events(PGFREE, 1 << order); >> - free_one_page(page_zone(page), page, pfn, order, migratetype); >> + free_one_page(page_zone(page), page, pfn, order, migratetype, true); >> local_irq_restore(flags); >> } >> >> @@ -2969,7 +2971,7 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn) >> */ >> if (migratetype >= MIGRATE_PCPTYPES) { >> if (unlikely(is_migrate_isolate(migratetype))) { >> - free_one_page(zone, page, pfn, 0, migratetype); >> + free_one_page(zone, page, pfn, 0, migratetype, true); >> return; >> } >> migratetype = MIGRATE_MOVABLE; >> 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. > >> +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. > >> + 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. > 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? > >> + zone_idx = zone_idx(zone); >> +#ifdef CONFIG_ZONE_DEVICE >> + if (zone_idx == ZONE_DEVICE) >> + continue; >> +#endif >> + spin_lock(&zone->lock); >> + if (free_area[zone_idx].base_pfn) { >> + free_area[zone_idx].base_pfn = >> + min(free_area[zone_idx].base_pfn, >> + zone->zone_start_pfn); >> + free_area[zone_idx].end_pfn = >> + max(free_area[zone_idx].end_pfn, >> + zone->zone_start_pfn + >> + zone->spanned_pages); >> + } else { >> + free_area[zone_idx].base_pfn = >> + zone->zone_start_pfn; >> + free_area[zone_idx].end_pfn = >> + zone->zone_start_pfn + >> + zone->spanned_pages; >> + } >> + spin_unlock(&zone->lock); >> + } >> + >> + for (zone_idx = 0; zone_idx < MAX_NR_ZONES; zone_idx++) { >> + unsigned long pages = free_area[zone_idx].end_pfn - >> + free_area[zone_idx].base_pfn; >> + bitmap_size = (pages >> PAGE_HINTING_MIN_ORDER) + 1; >> + if (!bitmap_size) >> + continue; >> + free_area[zone_idx].bitmap = bitmap_zalloc(bitmap_size, >> + GFP_KERNEL); >> + if (!free_area[zone_idx].bitmap) { >> + free_area_cleanup(zone_idx); >> + mutex_unlock(&page_hinting_init); >> + return -ENOMEM; >> + } >> + free_area[zone_idx].nbits = bitmap_size; >> + } > So this is the bit that still needs to address hotplug right? Yes, hotplug still needs to be addressed. > I would > imagine you need to reallocate this if the spanned_pages range changes > correct? > >> + page_hitning_conf = conf; >> + INIT_WORK(&hinting_work, init_hinting_wq); >> + ret = 0; >> + } >> + mutex_unlock(&page_hinting_init); >> + return ret; >> +} >> +EXPORT_SYMBOL_GPL(page_hinting_enable); >> + >> +void page_hinting_disable(void) >> +{ >> + cancel_work_sync(&hinting_work); >> + page_hitning_conf = NULL; >> + free_area_cleanup(MAX_NR_ZONES); >> +} >> +EXPORT_SYMBOL_GPL(page_hinting_disable); >> + >> +static unsigned long pfn_to_bit(struct page *page, int zone_idx) >> +{ >> + unsigned long bitnr; >> + >> + bitnr = (page_to_pfn(page) - free_area[zone_idx].base_pfn) >> + >> PAGE_HINTING_MIN_ORDER; >> + return bitnr; >> +} >> + >> +static void release_buddy_pages(struct list_head *pages) >> +{ >> + int mt = 0, zone_idx, order; >> + struct page *page, *next; >> + unsigned long bitnr; >> + struct zone *zone; >> + >> + list_for_each_entry_safe(page, next, pages, lru) { >> + zone_idx = page_zonenum(page); >> + zone = page_zone(page); >> + bitnr = pfn_to_bit(page, zone_idx); >> + spin_lock(&zone->lock); >> + list_del(&page->lru); >> + order = page_private(page); >> + set_page_private(page, 0); >> + mt = get_pageblock_migratetype(page); >> + __free_one_page(page, page_to_pfn(page), zone, >> + order, mt, false); >> + spin_unlock(&zone->lock); >> + } >> +} >> + >> +static void bm_set_pfn(struct page *page) >> +{ >> + struct zone *zone = page_zone(page); >> + int zone_idx = page_zonenum(page); >> + unsigned long bitnr = 0; >> + >> + lockdep_assert_held(&zone->lock); >> + bitnr = pfn_to_bit(page, zone_idx); >> + /* >> + * TODO: fix possible underflows. >> + */ >> + if (free_area[zone_idx].bitmap && >> + bitnr < free_area[zone_idx].nbits && >> + !test_and_set_bit(bitnr, free_area[zone_idx].bitmap)) >> + atomic_inc(&free_area[zone_idx].free_pages); >> +} >> + >> +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? > >> +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. > > In my patches I resolved this by looping through all of the zones, > however your approach is missing the necessary pieces to make that > safe as you could end up in a soft lockup with the scanning thread > spinning on a noisy system. > >> + zone_idx = zone_idx(page_zone(page)); >> + if (atomic_read(&free_area[zone_idx].free_pages) >= >> + page_hitning_conf->max_pages) { >> + int cpu = smp_processor_id(); >> + >> + queue_work_on(cpu, system_wq, &hinting_work); >> + } >> +} -- Thanks Nitesh