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Subject[RFC][Patch v9 1/6] KVM: Guest free page hinting support
Date
This patch adds the following:
1. Functional skeleton for the guest implementation. It enables the
guest to maintain the PFN of head buddy free pages of order
FREE_PAGE_HINTING_MIN_ORDER (currently defined as MAX_ORDER - 1)
in a per-cpu array.
Guest uses guest_free_page_enqueue() to enqueue the free pages post buddy
merging to the above mentioned per-cpu array.
guest_free_page_try_hinting() is used to initiate hinting operation once
the collected entries of the per-cpu array reaches or exceeds
HINTING_THRESHOLD (128). Having larger array size(MAX_FGPT_ENTRIES = 256)
than HINTING_THRESHOLD allows us to capture more pages specifically when
guest_free_page_enqueue() is called from free_pcppages_bulk().
For now guest_free_page_hinting() just resets the array index to continue
capturing of the freed pages.
2. Enables the support for x86 architecture.

Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
---
arch/x86/Kbuild | 2 +-
arch/x86/kvm/Kconfig | 8 +++
arch/x86/kvm/Makefile | 2 +
include/linux/page_hinting.h | 15 ++++++
mm/page_alloc.c | 5 ++
virt/kvm/page_hinting.c | 98 ++++++++++++++++++++++++++++++++++++
6 files changed, 129 insertions(+), 1 deletion(-)
create mode 100644 include/linux/page_hinting.h
create mode 100644 virt/kvm/page_hinting.c

diff --git a/arch/x86/Kbuild b/arch/x86/Kbuild
index c625f57472f7..3244df4ee311 100644
--- a/arch/x86/Kbuild
+++ b/arch/x86/Kbuild
@@ -2,7 +2,7 @@ obj-y += entry/

obj-$(CONFIG_PERF_EVENTS) += events/

-obj-$(CONFIG_KVM) += kvm/
+obj-$(subst m,y,$(CONFIG_KVM)) += kvm/

# Xen paravirtualization support
obj-$(CONFIG_XEN) += xen/
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 72fa955f4a15..2fae31459706 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -96,6 +96,14 @@ config KVM_MMU_AUDIT
This option adds a R/W kVM module parameter 'mmu_audit', which allows
auditing of KVM MMU events at runtime.

+# KVM_FREE_PAGE_HINTING will allow the guest to report the free pages to the
+# host in regular interval of time.
+config KVM_FREE_PAGE_HINTING
+ def_bool y
+ depends on KVM
+ select VIRTIO
+ select VIRTIO_BALLOON
+
# OK, it's a little counter-intuitive to do this, but it puts it neatly under
# the virtualization menu.
source "drivers/vhost/Kconfig"
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index 69b3a7c30013..78640a80501e 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -16,6 +16,8 @@ kvm-y += x86.o mmu.o emulate.o i8259.o irq.o lapic.o \
i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
hyperv.o page_track.o debugfs.o

+obj-$(CONFIG_KVM_FREE_PAGE_HINTING) += $(KVM)/page_hinting.o
+
kvm-intel-y += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o vmx/evmcs.o vmx/nested.o
kvm-amd-y += svm.o pmu_amd.o

diff --git a/include/linux/page_hinting.h b/include/linux/page_hinting.h
new file mode 100644
index 000000000000..90254c582789
--- /dev/null
+++ b/include/linux/page_hinting.h
@@ -0,0 +1,15 @@
+#include <linux/gfp.h>
+/*
+ * Size of the array which is used to store the freed pages is defined by
+ * MAX_FGPT_ENTRIES.
+ */
+#define MAX_FGPT_ENTRIES 256
+/*
+ * Threshold value after which hinting needs to be initiated on the captured
+ * free pages.
+ */
+#define HINTING_THRESHOLD 128
+#define FREE_PAGE_HINTING_MIN_ORDER (MAX_ORDER - 1)
+
+void guest_free_page_enqueue(struct page *page, int order);
+void guest_free_page_try_hinting(void);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d295c9bc01a8..684d047f33ee 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -67,6 +67,7 @@
#include <linux/lockdep.h>
#include <linux/nmi.h>
#include <linux/psi.h>
+#include <linux/page_hinting.h>

#include <asm/sections.h>
#include <asm/tlbflush.h>
@@ -1194,9 +1195,11 @@ static void free_pcppages_bulk(struct zone *zone, int count,
mt = get_pageblock_migratetype(page);

__free_one_page(page, page_to_pfn(page), zone, 0, mt);
+ guest_free_page_enqueue(page, 0);
trace_mm_page_pcpu_drain(page, 0, mt);
}
spin_unlock(&zone->lock);
+ guest_free_page_try_hinting();
}

static void free_one_page(struct zone *zone,
@@ -1210,7 +1213,9 @@ static void free_one_page(struct zone *zone,
migratetype = get_pfnblock_migratetype(page, pfn);
}
__free_one_page(page, pfn, zone, order, migratetype);
+ guest_free_page_enqueue(page, order);
spin_unlock(&zone->lock);
+ guest_free_page_try_hinting();
}

static void __meminit __init_single_page(struct page *page, unsigned long pfn,
diff --git a/virt/kvm/page_hinting.c b/virt/kvm/page_hinting.c
new file mode 100644
index 000000000000..48b4b5e796b0
--- /dev/null
+++ b/virt/kvm/page_hinting.c
@@ -0,0 +1,98 @@
+#include <linux/mm.h>
+#include <linux/page_hinting.h>
+
+/*
+ * struct guest_free_pages- holds array of guest freed PFN's along with an
+ * index variable to track total freed PFN's.
+ * @free_pfn_arr: array to store the page frame number of all the pages which
+ * are freed by the guest.
+ * @guest_free_pages_idx: index to track the number entries stored in
+ * free_pfn_arr.
+ */
+struct guest_free_pages {
+ unsigned long free_page_arr[MAX_FGPT_ENTRIES];
+ int free_pages_idx;
+};
+
+DEFINE_PER_CPU(struct guest_free_pages, free_pages_obj);
+
+struct page *get_buddy_page(struct page *page)
+{
+ unsigned long pfn = page_to_pfn(page);
+ unsigned int order;
+
+ for (order = 0; order < MAX_ORDER; order++) {
+ struct page *page_head = page - (pfn & ((1 << order) - 1));
+
+ if (PageBuddy(page_head) && page_private(page_head) >= order)
+ return page_head;
+ }
+ return NULL;
+}
+
+static void guest_free_page_hinting(void)
+{
+ struct guest_free_pages *hinting_obj = &get_cpu_var(free_pages_obj);
+
+ hinting_obj->free_pages_idx = 0;
+ put_cpu_var(hinting_obj);
+}
+
+int if_exist(struct page *page)
+{
+ int i = 0;
+ struct guest_free_pages *hinting_obj = this_cpu_ptr(&free_pages_obj);
+
+ while (i < MAX_FGPT_ENTRIES) {
+ if (page_to_pfn(page) == hinting_obj->free_page_arr[i])
+ return 1;
+ i++;
+ }
+ return 0;
+}
+
+void guest_free_page_enqueue(struct page *page, int order)
+{
+ unsigned long flags;
+ struct guest_free_pages *hinting_obj;
+ int l_idx;
+
+ /*
+ * use of global variables may trigger a race condition between irq and
+ * process context causing unwanted overwrites. This will be replaced
+ * with a better solution to prevent such race conditions.
+ */
+ local_irq_save(flags);
+ hinting_obj = this_cpu_ptr(&free_pages_obj);
+ l_idx = hinting_obj->free_pages_idx;
+ if (l_idx != MAX_FGPT_ENTRIES) {
+ if (PageBuddy(page) && page_private(page) >=
+ FREE_PAGE_HINTING_MIN_ORDER) {
+ hinting_obj->free_page_arr[l_idx] = page_to_pfn(page);
+ hinting_obj->free_pages_idx += 1;
+ } else {
+ struct page *buddy_page = get_buddy_page(page);
+
+ if (buddy_page && page_private(buddy_page) >=
+ FREE_PAGE_HINTING_MIN_ORDER &&
+ !if_exist(buddy_page)) {
+ unsigned long buddy_pfn =
+ page_to_pfn(buddy_page);
+
+ hinting_obj->free_page_arr[l_idx] =
+ buddy_pfn;
+ hinting_obj->free_pages_idx += 1;
+ }
+ }
+ }
+ local_irq_restore(flags);
+}
+
+void guest_free_page_try_hinting(void)
+{
+ struct guest_free_pages *hinting_obj;
+
+ hinting_obj = this_cpu_ptr(&free_pages_obj);
+ if (hinting_obj->free_pages_idx >= HINTING_THRESHOLD)
+ guest_free_page_hinting();
+}
--
2.17.2
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