* Re: [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing [not found] <A221FEC9-71CE-4D0A-9F39-F75C337B5D22@contoso.com> @ 2021-03-11 1:05 ` Alexander Duyck 0 siblings, 0 replies; 2+ messages in thread From: Alexander Duyck @ 2021-03-11 1:05 UTC (permalink / raw) To: Bodeddula, Balasubramaniam Cc: aarcange, akpm, alexander.h.duyck, dan.j.williams, dave.hansen, david, konrad.wilk, kvm, lcapitulino, linux-kernel, linux-mm, mgorman, mhocko, mst, nitesh, osalvador, pagupta, pbonzini, riel, vbabka, wei.w.wang, willy, yang.zhang.wz, Graf (AWS), Alexander, Herrenschmidt, Benjamin Hi Bala, There was a similar effort several months ago that was trying to do this in conjunction with pre-zeroing of pages. I suspect if you wanted to you could probably pick up some of their patch set and work with that. It can be found at: https://www.spinics.net/lists/linux-mm/msg239735.html Thanks. - Alex On Tue, Mar 9, 2021 at 12:13 AM Bodeddula, Balasubramaniam <bodeddub@amazon.com> wrote: > > Hi Alexander, > > > > My team was evaluating FPR and observed that these patches don’t report memory for deallocated hugeapages directly and need to cycle through buddy allocator. For example, say we need to allocate a maximum of 12 * 1G hugepages (by setting nr_hugepages), use 8 * 1G hugepages, and then deallocate 4 * 1G hugepages. Unlike regular 4K pages, this 4G worth of memory will not be reported until we set nr_hugepages to 8 (wait sometime(?) for FPR to do its work) and set it back again to 12. While this works fine in theory, in practice, setting nr_hugepages to 12 could fail too due to fragmentation (this could depend on other processes memory usage behavior). > > > > If FPR could report this free memory without cycling through buddy allocator, it makes the solution more robust. I am looking for advice on how feasible this approach is and what would be the effort for building this functionality. In general, if there are other thoughts on how we can address this, please do let me know. > > > > Thanks, > > bala ^ permalink raw reply [flat|nested] 2+ messages in thread
* [PATCH v17 0/9] mm / virtio: Provide support for free page reporting @ 2020-02-11 22:45 Alexander Duyck 2020-02-11 22:46 ` [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck 0 siblings, 1 reply; 2+ messages in thread From: Alexander Duyck @ 2020-02-11 22:45 UTC (permalink / raw) To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador This series provides an asynchronous means of reporting free guest pages to a hypervisor so that the memory associated with those pages can be dropped and reused by other processes and/or guests on the host. Using this it is possible to avoid unnecessary I/O to disk and greatly improve performance in the case of memory overcommit on the host. When enabled we will be performing a scan of free memory every 2 seconds while pages of sufficiently high order are being freed. In each pass at least one sixteenth of each free list will be reported. By doing this we avoid racing against other threads that may be causing a high amount of memory churn. The lowest page order currently scanned when reporting pages is pageblock_order so that this feature will not interfere with the use of Transparent Huge Pages in the case of virtualization. Currently this is only in use by virtio-balloon however there is the hope that at some point in the future other hypervisors might be able to make use of it. In the virtio-balloon/QEMU implementation the hypervisor is currently using MADV_DONTNEED to indicate to the host kernel that the page is currently free. It will be zeroed and faulted back into the guest the next time the page is accessed. To track if a page is reported or not the Uptodate flag was repurposed and used as a Reported flag for Buddy pages. We walk though the free list isolating pages and adding them to the scatterlist until we either encounter the end of the list or have processed at least one sixteenth of the pages that were listed in nr_free prior to us starting. If we fill the scatterlist before we reach the end of the list we rotate the list so that the first unreported page we encounter is moved to the head of the list as that is where we will resume after we have freed the reported pages back into the tail of the list. Below are the results from various benchmarks. I primarily focused on two tests. The first is the will-it-scale/page_fault2 test, and the other is a modified version of will-it-scale/page_fault1 that was enabled to use THP. I did this as it allows for better visibility into different parts of the memory subsystem. The guest is running with 32G for RAM on one node of a E5-2630 v3. The host has had some features such as CPU turbo disabled in the BIOS. Test page_fault1 (THP) page_fault2 Name tasks Process Iter STDEV Process Iter STDEV Baseline 1 1012402.50 0.14% 361855.25 0.81% 16 8827457.25 0.09% 3282347.00 0.34% Patches Applied 1 1007897.00 0.23% 361887.00 0.26% 16 8784741.75 0.39% 3240669.25 0.48% Patches Enabled 1 1010227.50 0.39% 359749.25 0.56% 16 8756219.00 0.24% 3226608.75 0.97% Patches Enabled 1 1050982.00 4.26% 357966.25 0.14% page shuffle 16 8672601.25 0.49% 3223177.75 0.40% Patches enabled 1 1003238.00 0.22% 360211.00 0.22% shuffle w/ RFC 16 8767010.50 0.32% 3199874.00 0.71% The results above are for a baseline with a linux-next-20191219 kernel, that kernel with this patch set applied but page reporting disabled in virtio-balloon, the patches applied and page reporting fully enabled, the patches enabled with page shuffling enabled, and the patches applied with page shuffling enabled and an RFC patch that makes used of MADV_FREE in QEMU. These results include the deviation seen between the average value reported here versus the high and/or low value. I observed that during the test memory usage for the first three tests never dropped whereas with the patches fully enabled the VM would drop to using only a few GB of the host's memory when switching from memhog to page fault tests. Any of the overhead visible with this patch set enabled seems due to page faults caused by accessing the reported pages and the host zeroing the page before giving it back to the guest. This overhead is much more visible when using THP than with standard 4K pages. In addition page shuffling seemed to increase the amount of faults generated due to an increase in memory churn. The overehad is reduced when using MADV_FREE as we can avoid the extra zeroing of the pages when they are reintroduced to the host, as can be seen when the RFC is applied with shuffling enabled. The overall guest size is kept fairly small to only a few GB while the test is running. If the host memory were oversubscribed this patch set should result in a performance improvement as swapping memory in the host can be avoided. A brief history on the background of free page reporting can be found at: https://lore.kernel.org/lkml/29f43d5796feed0dec8e8bb98b187d9dac03b900.camel@linux.intel.com/ Changes from v14: https://lore.kernel.org/lkml/20191119214454.24996.66289.stgit@localhost.localdomain/ Renamed "unused page reporting" to "free page reporting" Updated code, kconfig, and patch descriptions Split out patch for __free_isolated_page Renamed function to __putback_isolated_page Rewrote core reporting functionality Added logic to reschedule worker in 2 seconds instead of run to completion Removed reported_pages statistics Removed REPORTING_REQUESTED bit used in zone flags Replaced page_reporting_dev_info refcount with state variable Removed scatterlist from page_reporting_dev_info Removed capacity from page reporting device Added dynamic scatterlist allocation/free at start/end of reporting process Updated __free_one_page so that reported pages are not always added to tail Added logic to handle error from report function Updated virtio-balloon patch that adds support for page reporting Updated patch description to try and highlight differences in approaches Updated logic to reflect that we cannot limit the scatterlist from device Added logic to return error from report function Moved documentation patch to end of patch set Changes from v15: https://lore.kernel.org/lkml/20191205161928.19548.41654.stgit@localhost.localdomain/ Rebased on linux-next-20191219 Split out patches for budget and moving head to last page processed Updated budget code to reduce how much memory is reported per pass Added logic to also rotate the list if we exit due a page isolation failure Added migratetype as argument in __putback_isolated_page Changes from v16: https://lore.kernel.org/lkml/20200103210509.29237.18426.stgit@localhost.localdomain/ Rebased on linux-next-20200122 Updated patch 2 to to account for removal of pr_info in __isolate_free_page Updated patch title for patches 7, 8, and 9 to included mm/page_reporting Changes from v16.1: https://lore.kernel.org/lkml/20200122173040.6142.39116.stgit@localhost.localdomain/ Rebased QEMU patches to latest Rebased on linux-next-20200211 Tweaked cover page to more accurately describe hinting process Verified results have not changed in significant way --- Alexander Duyck (9): mm: Adjust shuffle code to allow for future coalescing mm: Use zone and order instead of free area in free_list manipulators mm: Add function __putback_isolated_page mm: Introduce Reported pages virtio-balloon: Pull page poisoning config out of free page hinting virtio-balloon: Add support for providing free page reports to host mm/page_reporting: Rotate reported pages to the tail of the list mm/page_reporting: Add budget limit on how many pages can be reported per pass mm/page_reporting: Add free page reporting documentation Documentation/vm/free_page_reporting.rst | 41 +++ drivers/virtio/Kconfig | 1 drivers/virtio/virtio_balloon.c | 87 +++++++ include/linux/mmzone.h | 44 ---- include/linux/page-flags.h | 11 + include/linux/page_reporting.h | 26 ++ include/uapi/linux/virtio_balloon.h | 1 mm/Kconfig | 11 + mm/Makefile | 1 mm/internal.h | 2 mm/page_alloc.c | 164 ++++++++++---- mm/page_isolation.c | 6 mm/page_reporting.c | 364 ++++++++++++++++++++++++++++++ mm/page_reporting.h | 54 ++++ mm/shuffle.c | 12 - mm/shuffle.h | 6 16 files changed, 725 insertions(+), 106 deletions(-) create mode 100644 Documentation/vm/free_page_reporting.rst create mode 100644 include/linux/page_reporting.h create mode 100644 mm/page_reporting.c create mode 100644 mm/page_reporting.h -- ^ permalink raw reply [flat|nested] 2+ messages in thread
* [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing 2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck @ 2020-02-11 22:46 ` Alexander Duyck 0 siblings, 0 replies; 2+ messages in thread From: Alexander Duyck @ 2020-02-11 22:46 UTC (permalink / raw) To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador From: Alexander Duyck <alexander.h.duyck@linux.intel.com> Move the head/tail adding logic out of the shuffle code and into the __free_one_page function since ultimately that is where it is really needed anyway. By doing this we should be able to reduce the overhead and can consolidate all of the list addition bits in one spot. Acked-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com> --- include/linux/mmzone.h | 12 -------- mm/page_alloc.c | 71 ++++++++++++++++++++++++++++-------------------- mm/shuffle.c | 12 ++++---- mm/shuffle.h | 6 ++++ 4 files changed, 54 insertions(+), 47 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 462f6873905a..bdcd071ab67f 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -116,18 +116,6 @@ static inline void add_to_free_area_tail(struct page *page, struct free_area *ar area->nr_free++; } -#ifdef CONFIG_SHUFFLE_PAGE_ALLOCATOR -/* Used to preserve page allocation order entropy */ -void add_to_free_area_random(struct page *page, struct free_area *area, - int migratetype); -#else -static inline void add_to_free_area_random(struct page *page, - struct free_area *area, int migratetype) -{ - add_to_free_area(page, area, migratetype); -} -#endif - /* Used for pages which are on another list */ static inline void move_to_free_area(struct page *page, struct free_area *area, int migratetype) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3c4eb750a199..bf36cdfea07a 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -871,6 +871,36 @@ static inline struct capture_control *task_capc(struct zone *zone) #endif /* CONFIG_COMPACTION */ /* + * If this is not the largest possible page, check if the buddy + * of the next-highest order is free. If it is, it's possible + * that pages are being freed that will coalesce soon. In case, + * that is happening, add the free page to the tail of the list + * so it's less likely to be used soon and more likely to be merged + * as a higher order page + */ +static inline bool +buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn, + struct page *page, unsigned int order) +{ + struct page *higher_page, *higher_buddy; + unsigned long combined_pfn; + + if (order >= MAX_ORDER - 2) + return false; + + if (!pfn_valid_within(buddy_pfn)) + return false; + + combined_pfn = buddy_pfn & pfn; + higher_page = page + (combined_pfn - pfn); + buddy_pfn = __find_buddy_pfn(combined_pfn, order + 1); + higher_buddy = higher_page + (buddy_pfn - combined_pfn); + + return pfn_valid_within(buddy_pfn) && + page_is_buddy(higher_page, higher_buddy, order + 1); +} + +/* * Freeing function for a buddy system allocator. * * The concept of a buddy system is to maintain direct-mapped table @@ -899,11 +929,13 @@ static inline void __free_one_page(struct page *page, struct zone *zone, unsigned int order, int migratetype) { - unsigned long combined_pfn; + struct capture_control *capc = task_capc(zone); unsigned long uninitialized_var(buddy_pfn); - struct page *buddy; + unsigned long combined_pfn; + struct free_area *area; unsigned int max_order; - struct capture_control *capc = task_capc(zone); + struct page *buddy; + bool to_tail; max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1); @@ -972,35 +1004,16 @@ static inline void __free_one_page(struct page *page, done_merging: set_page_order(page, order); - /* - * If this is not the largest possible page, check if the buddy - * of the next-highest order is free. If it is, it's possible - * that pages are being freed that will coalesce soon. In case, - * that is happening, add the free page to the tail of the list - * so it's less likely to be used soon and more likely to be merged - * as a higher order page - */ - if ((order < MAX_ORDER-2) && pfn_valid_within(buddy_pfn) - && !is_shuffle_order(order)) { - struct page *higher_page, *higher_buddy; - combined_pfn = buddy_pfn & pfn; - higher_page = page + (combined_pfn - pfn); - buddy_pfn = __find_buddy_pfn(combined_pfn, order + 1); - higher_buddy = higher_page + (buddy_pfn - combined_pfn); - if (pfn_valid_within(buddy_pfn) && - page_is_buddy(higher_page, higher_buddy, order + 1)) { - add_to_free_area_tail(page, &zone->free_area[order], - migratetype); - return; - } - } - + area = &zone->free_area[order]; if (is_shuffle_order(order)) - add_to_free_area_random(page, &zone->free_area[order], - migratetype); + to_tail = shuffle_pick_tail(); else - add_to_free_area(page, &zone->free_area[order], migratetype); + to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order); + if (to_tail) + add_to_free_area_tail(page, area, migratetype); + else + add_to_free_area(page, area, migratetype); } /* diff --git a/mm/shuffle.c b/mm/shuffle.c index b3fe97fd6654..e65d57f39486 100644 --- a/mm/shuffle.c +++ b/mm/shuffle.c @@ -183,11 +183,11 @@ void __meminit __shuffle_free_memory(pg_data_t *pgdat) shuffle_zone(z); } -void add_to_free_area_random(struct page *page, struct free_area *area, - int migratetype) +bool shuffle_pick_tail(void) { static u64 rand; static u8 rand_bits; + bool ret; /* * The lack of locking is deliberate. If 2 threads race to @@ -198,10 +198,10 @@ void add_to_free_area_random(struct page *page, struct free_area *area, rand = get_random_u64(); } - if (rand & 1) - add_to_free_area(page, area, migratetype); - else - add_to_free_area_tail(page, area, migratetype); + ret = rand & 1; + rand_bits--; rand >>= 1; + + return ret; } diff --git a/mm/shuffle.h b/mm/shuffle.h index 777a257a0d2f..4d79f03b6658 100644 --- a/mm/shuffle.h +++ b/mm/shuffle.h @@ -22,6 +22,7 @@ enum mm_shuffle_ctl { DECLARE_STATIC_KEY_FALSE(page_alloc_shuffle_key); extern void page_alloc_shuffle(enum mm_shuffle_ctl ctl); extern void __shuffle_free_memory(pg_data_t *pgdat); +extern bool shuffle_pick_tail(void); static inline void shuffle_free_memory(pg_data_t *pgdat) { if (!static_branch_unlikely(&page_alloc_shuffle_key)) @@ -44,6 +45,11 @@ static inline bool is_shuffle_order(int order) return order >= SHUFFLE_ORDER; } #else +static inline bool shuffle_pick_tail(void) +{ + return false; +} + static inline void shuffle_free_memory(pg_data_t *pgdat) { } ^ permalink raw reply related [flat|nested] 2+ messages in thread
end of thread, other threads:[~2021-03-11 1:06 UTC | newest] Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <A221FEC9-71CE-4D0A-9F39-F75C337B5D22@contoso.com> 2021-03-11 1:05 ` [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck 2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck 2020-02-11 22:46 ` [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).