Hot/cold page tracking using hardware counters

Based on the work from Vaibhav Jain <vaibhav@linux.ibm.com>
and Sandipan Das <sandipan@linux.ibm.com>

Not-yet-Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

arch/powerpc/Kconfig

@@ -1025,6 +1025,15 @@ config PPC_RTAS_FILTER
 	  Say Y unless you know what you are doing and the filter is causing
 	  problems for you.
 
+config PPC_HCA_HOTNESS
+	prompt "PowerPC HCA engine based page hotness"
+	def_bool y
+	depends on PPC_BOOK3S_64 && LRU_GEN
+	help
+	  Use HCA engine to find page hotness
+
+	  If unsure, say N.
+
 endmenu
 
 config ISA_DMA_API

arch/powerpc/include/asm/hca.h

@@ -0,0 +1,239 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * Copyright 2021, Sandipan Das, IBM Corp.
+ * Configuration helpers for the Hot-Cold Affinity helper
+ */
+
+#ifndef _ASM_POWERPC_HCA_H
+#define _ASM_POWERPC_HCA_H
+
+#include <linux/types.h>
+#include <linux/bitops.h>
+#include <linux/minmax.h>
+
+#define KB	(1024UL)
+#define MB	(1024 * KB)
+#define GB	(1024 * MB)
+#define TB	(1024 * GB)
+
+#define HCA_ENGINES_PER_CHIP	1 /* 2 */
+#define HCA_ENTRY_SIZE		8
+
+#ifdef CONFIG_PPC_4K_PAGES
+#define HCA_PAGE_SIZE		(4 * KB)
+#else  /* CONFIG_PPC_64K_PAGES */
+#define HCA_PAGE_SIZE		(64 * KB)
+#endif /* CONFIG_PPC_4K_PAGES  */
+
+/*
+ * @m: The counter overflow mask
+ *
+ * Supported overflow masks are 16, 32, 64 ... 4096. The page stats in
+ * the HCA cache are written back to memory once the count reaches @m.
+ */
+#define HCA_OVERFLOW_MASK(m)		min((u64)4096, max((u64)16, (u64)roundup_pow_of_two(m)))
+#define HCA_OVERFLOW_MASK_DEFAULT	4096
+
+/*
+ * @m: The command sampling mode
+ *
+ * Supported command sampling modes are
+ * 	0 -> No sampling (capture all commands)
+ * 	1 -> Sample 1 of 16 commands
+ * 	2 -> Sample 1 of 32 commands
+ * 	3 -> Dynamic sampling (configured separately)
+ *
+ * The HCA fabric update traffic is reduced at the cost of accuracy. The
+ * counts are scaled based on the sampling rate, i.e. if a single command
+ * is seen when 1 of 16 mode is used, the corresponding page count will be
+ * incremented by 16.
+ */
+#define HCA_SAMPLING_MODE(m)		min((u64)3, max((u64)0, (u64)(m) & 0x3))
+#define HCA_SAMPLING_MODE_DEFAULT	3
+
+/*
+ * @p: The command sampling period (in cycles)
+ *
+ * Supported command sampling periods are 256, 512, 1024 ... 65536 cycles.
+ * HCA update commands sent to the fabric are counted every @p cycles.
+ *
+ * Only used when dynamic sampling is enabled.
+ * Actual period is = (value+1) * 256
+ *
+ */
+#define HCA_SAMPLING_PERIOD(p)		min((u64)65536, max((u64)256, (u64)roundup_pow_of_two(p)))
+#define HCA_SAMPLING_PERIOD_DEFAULT	0
+
+/*
+ * @t: The command threshold
+ *
+ * Supported command thresholds are 0, 1, 2 ... 255 commands.
+ *
+ * With the upper command threshold, the sampling rate will reduce when
+ * more than @t number of update commands are detected within a sampling
+ * period.
+ *
+ * With the lower command threshold, the sampling rate will increase when
+ * fewer than @t number of update commands are detected within a sampling
+ * period.
+ *
+ * Only used when dynamic sampling is enabled.
+ */
+#define HCA_SAMPLING_LOWER_THRESH(t)		min((u64)255, (u64)(t))
+#define HCA_SAMPLING_LOWER_THRESH_DEFAULT	64UL
+
+/*
+ * @t: The command threshold
+ *
+ * Supported command thresholds are 0, 1, 2 ... 255 commands.
+ *
+ * With the upper command threshold, the sampling rate will reduce when
+ * more than @t number of update commands are detected within a sampling
+ * period.
+ *
+ * With the lower command threshold, the sampling rate will increase when
+ * fewer than @t number of update commands are detected within a sampling
+ * period.
+ *
+ * Only used when dynamic sampling is enabled.
+ */
+#define HCA_SAMPLING_UPPER_THRESH(t)		min((u64)255, (u64)(t))
+#define HCA_SAMPLING_UPPER_THRESH_DEFAULT	255UL
+
+/*
+ * @s: The monitor region size (in bytes)
+ *
+ * Supported monitor region sizes are 16GB, 32GB, 64GB ... 512TB. The
+ * minimum and maximum region sizes are always guaranteed to be 16GB
+ * and 512TB respectively if the specified value is out of bounds.
+ */
+#define HCA_MONITOR_SIZE(s)		min((u64)512 * TB, max((u64)16 * GB, (u64)roundup_pow_of_two(s)))
+//#define HCA_MONITOR_SIZE_DEFAULT	(16 * GB)
+
+/*
+ * @b: The monitor region base
+ * @s: The monitor region size (in bytes)
+ *
+ * The monitor region base address must be aligned to its size.
+ */
+#define HCA_MONITOR_BASE(b, s)		ALIGN((u64)(b), HCA_MONITOR_SIZE(s))
+//#define HCA_MONITOR_BASE_DEFAULT	0
+
+/*
+ * @s: The monitor region size
+ *
+ * The counter region size is directly derived from the monitor region
+ * size and the page size.
+ */
+#define HCA_COUNTER_SIZE(s)		((HCA_MONITOR_SIZE(s) * (u64)HCA_ENTRY_SIZE) / PAGE_SIZE)
+#define HCA_COUNTER_SIZE_DEFAULT	0
+#define HCA_COUNTER_BASE_DEFAULT	0
+
+/*
+ * @d: The decay delay (in ns)
+ *
+ * Decay delay defines the interval between updates to HCA cachelines of
+ * 128 bytes. This parameter is not indicative of the absolute time taken
+ * to apply decay updates to the entire counter region. However, that can
+ * be derived from the configured decay delay.
+ *
+ * E.g. monitoring a 512GB region of 64kB pages requires a 64MB counter
+ * region. To apply one round of decay updates to the entire region will
+ * require (64M / 128) = 524288 HCA cache lines to be updated. If @d is
+ * 2048, (524288 * 2048) ns = ~1.07s is required to update the entire
+ * counter region.
+ *
+ * If the delay is set to 0, the decay feature is disabled. Otherwise,
+ * supported decay delay periods are 16ns, 32ns, 64ns ... 147573952589s.
+ * Since @d is in the nanosecond scale, representing the upper bound is
+ * not possible with a 64-bit integer. Moreover, such large delays are
+ * impractical for most intents and purposes. So, while the hardware can
+ * support it, the maximum configurable decay delay is restricted to
+ * 9223372036854775808ns. The minimum and maximum decay delays are always
+ * guaranteed to be 32ns and 9223372036854775808ns respectively if the
+ * specified value is out of bounds.
+ */
+#define HCA_DECAY_DELAY(d)		((d) ? min((uint64_t)9223372036854775808ULL, max((uint64_t)16, (uint64_t)roundup_pow_of_two(d))) : (uint64_t)0)
+/* 1 msec */
+#define HCA_DECAY_DELAY_DEFAULT		1
+
+/* Entry constants and helpers */
+#define HCA_ENTRY_SIZE		8
+
+/*
+ * @v: The raw value of the entry
+ * @s: The start of the bitfield
+ * @n: The length of the bitfield
+ */
+#define HCA_ENTRY_FIELD(v, s, n)	(((v) >> ( 64 - (s + n))) & ((1UL << (n)) - 1))
+
+/*
+ * The value of the HCA count is : 4^e * m
+ * e = X[0:3], m = X[4:15]
+ */
+#define HCA_ENTRY_COUNT_EXP(e)		HCA_ENTRY_FIELD((e), 0, 4)
+#define HCA_ENTRY_COUNT_MNT(e)		HCA_ENTRY_FIELD((e), 4, 12)
+#define HCA_ENTRY_COUNT(e)		((1UL << (2 * HCA_ENTRY_COUNT_EXP(e))) * HCA_ENTRY_COUNT_MNT(e))
+
+#define HCA_ENTRY_AGE(e)		HCA_ENTRY_FIELD((e), 16, 3)
+
+#define HCA_ENTRY_GEN(e)		HCA_ENTRY_FIELD((e), 19, 1)
+
+/*
+ * The value of the HCA prev_count is : 4^e * m
+ * e = X[0:3], m = X[4:11]
+ */
+#define HCA_ENTRY_PREV_COUNT_EXP_LENGTH	4
+#define HCA_ENTRY_PREV_COUNT_EXP_START	20
+#define HCA_ENTRY_PREV_COUNT_MNT_LENGTH	8
+#define HCA_ENTRY_PREV_COUNT_MNT_START	24
+#define HCA_ENTRY_PREV_COUNT_EXP(e)	HCA_ENTRY_FIELD((e), 20, 4)
+#define HCA_ENTRY_PREV_COUNT_MNT(e)	HCA_ENTRY_FIELD((e), 24, 8)
+#define HCA_ENTRY_PREV_COUNT(e)		((1UL << (2 * HCA_ENTRY_PREV_COUNT_EXP(e))) * HCA_ENTRY_PREV_COUNT_MNT(e))
+
+#define HCA_ENTRY_TIMELOG_LENGTH	7
+#define HCA_ENTRY_TIMELOG_START		32
+#define HCA_ENTRY_TIMELOG(e)		HCA_ENTRY_FIELD((e), 32, 7)
+
+#define HCA_ENTRY_SOCKETID_COUNT	5
+#define HCA_ENTRY_SOCKETID_LENGTH	5
+#define HCA_ENTRY_SOCKETID_START(s)	(39 + (s) * HCA_ENTRY_SOCKETID_LENGTH)
+#define HCA_ENTRY_SOCKETID(e, s)	HCA_ENTRY_FIELD((e), HCA_ENTRY_SOCKETID_START(s), HCA_ENTRY_SOCKETID_LENGTH)
+
+struct hca_entry {
+	unsigned long count;
+	uint8_t age;
+	uint8_t gen;
+	unsigned long prev_count;
+	uint8_t timelog;
+	uint8_t socketid[HCA_ENTRY_SOCKETID_COUNT];
+};
+
+static inline unsigned long hotness_score(struct hca_entry * entry)
+{
+	unsigned long hotness;
+
+	/*
+	 * Give more weightage to the prev_count because it got
+	 * historical values. Take smaller part of count as we
+	 * age more because prev_count would be a better approximation.
+	 * We still need to consider count to accomidate spike in access.
+	 * + 1 with age to handle age == 0.
+	 */
+	hotness = entry->prev_count + (entry->count / (entry->age + 1));
+
+	return hotness;
+}
+
+extern bool hca_lru_age;
+extern bool hca_lru_evict;
+extern int  (*hca_pfn_entry)(unsigned long pfn, struct hca_entry *entry);
+extern bool (*hca_node_enabled)(int numa_node);
+extern void (*hca_backend_node_debugfs_init)(int numa_node, struct dentry *node_dentry);
+extern void (*hca_backend_debugfs_init)(struct dentry *root_dentry);
+extern int  (*hca_clear_entry)(unsigned long pfn);
+int map_hca_lru_seq(struct lruvec *lruvec, struct folio *folio);
+bool hca_try_to_inc_max_seq(struct lruvec *lruvec, unsigned long nr_to_scan, unsigned long max_seq);
+void restablish_hotness_range(int node);
+#endif /* _ASM_POWERPC_HCA_H */

arch/powerpc/include/asm/page.h

@@ -319,6 +319,11 @@ void arch_free_page(struct page *page, int order);
 #define HAVE_ARCH_FREE_PAGE
 #endif
 
+#ifdef CONFIG_PPC_HCA_HOTNESS
+void arch_alloc_page(struct page *page, int order);
+#define HAVE_ARCH_ALLOC_PAGE
+#endif
+
 struct vm_area_struct;
 
 extern unsigned long kernstart_virt_addr;

arch/powerpc/mm/Makefile

@@ -19,3 +19,4 @@ obj-$(CONFIG_NOT_COHERENT_CACHE) += dma-noncoherent.o
 obj-$(CONFIG_PPC_COPRO_BASE)	+= copro_fault.o
 obj-$(CONFIG_PTDUMP_CORE)	+= ptdump/
 obj-$(CONFIG_KASAN)		+= kasan/
+obj-$(CONFIG_PPC_HCA_HOTNESS)	+= hca.o