Commit 30a5b536 authored by Dennis Zhou's avatar Dennis Zhou Committed by Tejun Heo
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percpu: expose statistics about percpu memory via debugfs



There is limited visibility into the use of percpu memory leaving us
unable to reason about correctness of parameters and overall use of
percpu memory. These counters and statistics aim to help understand
basic statistics about percpu memory such as number of allocations over
the lifetime, allocation sizes, and fragmentation.

New Config: PERCPU_STATS
Signed-off-by: default avatarDennis Zhou <dennisz@fb.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 8fa3ed80
......@@ -706,3 +706,11 @@ config ARCH_USES_HIGH_VMA_FLAGS
bool
config ARCH_HAS_PKEYS
bool
config PERCPU_STATS
bool "Collect percpu memory statistics"
default n
help
This feature collects and exposes statistics via debugfs. The
information includes global and per chunk statistics, which can
be used to help understand percpu memory usage.
......@@ -103,3 +103,4 @@ obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
obj-$(CONFIG_FRAME_VECTOR) += frame_vector.o
obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o
obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o
obj-$(CONFIG_PERCPU_STATS) += percpu-stats.o
......@@ -5,6 +5,11 @@
#include <linux/percpu.h>
struct pcpu_chunk {
#ifdef CONFIG_PERCPU_STATS
int nr_alloc; /* # of allocations */
size_t max_alloc_size; /* largest allocation size */
#endif
struct list_head list; /* linked to pcpu_slot lists */
int free_size; /* free bytes in the chunk */
int contig_hint; /* max contiguous size hint */
......@@ -18,6 +23,11 @@ struct pcpu_chunk {
void *data; /* chunk data */
int first_free; /* no free below this */
bool immutable; /* no [de]population allowed */
bool has_reserved; /* Indicates if chunk has reserved space
at the beginning. Reserved chunk will
contain reservation for static chunk.
Dynamic chunk will contain reservation
for static and reserved chunks. */
int nr_populated; /* # of populated pages */
unsigned long populated[]; /* populated bitmap */
};
......@@ -30,4 +40,125 @@ extern int pcpu_nr_slots;
extern struct pcpu_chunk *pcpu_first_chunk;
extern struct pcpu_chunk *pcpu_reserved_chunk;
#ifdef CONFIG_PERCPU_STATS
#include <linux/spinlock.h>
struct percpu_stats {
u64 nr_alloc; /* lifetime # of allocations */
u64 nr_dealloc; /* lifetime # of deallocations */
u64 nr_cur_alloc; /* current # of allocations */
u64 nr_max_alloc; /* max # of live allocations */
u32 nr_chunks; /* current # of live chunks */
u32 nr_max_chunks; /* max # of live chunks */
size_t min_alloc_size; /* min allocaiton size */
size_t max_alloc_size; /* max allocation size */
};
extern struct percpu_stats pcpu_stats;
extern struct pcpu_alloc_info pcpu_stats_ai;
/*
* For debug purposes. We don't care about the flexible array.
*/
static inline void pcpu_stats_save_ai(const struct pcpu_alloc_info *ai)
{
memcpy(&pcpu_stats_ai, ai, sizeof(struct pcpu_alloc_info));
/* initialize min_alloc_size to unit_size */
pcpu_stats.min_alloc_size = pcpu_stats_ai.unit_size;
}
/*
* pcpu_stats_area_alloc - increment area allocation stats
* @chunk: the location of the area being allocated
* @size: size of area to allocate in bytes
*
* CONTEXT:
* pcpu_lock.
*/
static inline void pcpu_stats_area_alloc(struct pcpu_chunk *chunk, size_t size)
{
lockdep_assert_held(&pcpu_lock);
pcpu_stats.nr_alloc++;
pcpu_stats.nr_cur_alloc++;
pcpu_stats.nr_max_alloc =
max(pcpu_stats.nr_max_alloc, pcpu_stats.nr_cur_alloc);
pcpu_stats.min_alloc_size =
min(pcpu_stats.min_alloc_size, size);
pcpu_stats.max_alloc_size =
max(pcpu_stats.max_alloc_size, size);
chunk->nr_alloc++;
chunk->max_alloc_size = max(chunk->max_alloc_size, size);
}
/*
* pcpu_stats_area_dealloc - decrement allocation stats
* @chunk: the location of the area being deallocated
*
* CONTEXT:
* pcpu_lock.
*/
static inline void pcpu_stats_area_dealloc(struct pcpu_chunk *chunk)
{
lockdep_assert_held(&pcpu_lock);
pcpu_stats.nr_dealloc++;
pcpu_stats.nr_cur_alloc--;
chunk->nr_alloc--;
}
/*
* pcpu_stats_chunk_alloc - increment chunk stats
*/
static inline void pcpu_stats_chunk_alloc(void)
{
spin_lock_irq(&pcpu_lock);
pcpu_stats.nr_chunks++;
pcpu_stats.nr_max_chunks =
max(pcpu_stats.nr_max_chunks, pcpu_stats.nr_chunks);
spin_unlock_irq(&pcpu_lock);
}
/*
* pcpu_stats_chunk_dealloc - decrement chunk stats
*/
static inline void pcpu_stats_chunk_dealloc(void)
{
spin_lock_irq(&pcpu_lock);
pcpu_stats.nr_chunks--;
spin_unlock_irq(&pcpu_lock);
}
#else
static inline void pcpu_stats_save_ai(const struct pcpu_alloc_info *ai)
{
}
static inline void pcpu_stats_area_alloc(struct pcpu_chunk *chunk, size_t size)
{
}
static inline void pcpu_stats_area_dealloc(struct pcpu_chunk *chunk)
{
}
static inline void pcpu_stats_chunk_alloc(void)
{
}
static inline void pcpu_stats_chunk_dealloc(void)
{
}
#endif /* !CONFIG_PERCPU_STATS */
#endif
......@@ -72,6 +72,8 @@ static struct pcpu_chunk *pcpu_create_chunk(void)
pcpu_chunk_populated(chunk, 0, nr_pages);
spin_unlock_irq(&pcpu_lock);
pcpu_stats_chunk_alloc();
return chunk;
}
......@@ -79,6 +81,8 @@ static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
{
const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
pcpu_stats_chunk_dealloc();
if (chunk && chunk->data)
__free_pages(chunk->data, order_base_2(nr_pages));
pcpu_free_chunk(chunk);
......
/*
* mm/percpu-debug.c
*
* Copyright (C) 2017 Facebook Inc.
* Copyright (C) 2017 Dennis Zhou <dennisz@fb.com>
*
* This file is released under the GPLv2.
*
* Prints statistics about the percpu allocator and backing chunks.
*/
#include <linux/debugfs.h>
#include <linux/list.h>
#include <linux/percpu.h>
#include <linux/seq_file.h>
#include <linux/sort.h>
#include <linux/vmalloc.h>
#include "percpu-internal.h"
#define P(X, Y) \
seq_printf(m, " %-24s: %8lld\n", X, (long long int)Y)
struct percpu_stats pcpu_stats;
struct pcpu_alloc_info pcpu_stats_ai;
static int cmpint(const void *a, const void *b)
{
return *(int *)a - *(int *)b;
}
/*
* Iterates over all chunks to find the max # of map entries used.
*/
static int find_max_map_used(void)
{
struct pcpu_chunk *chunk;
int slot, max_map_used;
max_map_used = 0;
for (slot = 0; slot < pcpu_nr_slots; slot++)
list_for_each_entry(chunk, &pcpu_slot[slot], list)
max_map_used = max(max_map_used, chunk->map_used);
return max_map_used;
}
/*
* Prints out chunk state. Fragmentation is considered between
* the beginning of the chunk to the last allocation.
*/
static void chunk_map_stats(struct seq_file *m, struct pcpu_chunk *chunk,
void *buffer)
{
int i, s_index, last_alloc, alloc_sign, as_len;
int *alloc_sizes, *p;
/* statistics */
int sum_frag = 0, max_frag = 0;
int cur_min_alloc = 0, cur_med_alloc = 0, cur_max_alloc = 0;
alloc_sizes = buffer;
s_index = chunk->has_reserved ? 1 : 0;
/* find last allocation */
last_alloc = -1;
for (i = chunk->map_used - 1; i >= s_index; i--) {
if (chunk->map[i] & 1) {
last_alloc = i;
break;
}
}
/* if the chunk is not empty - ignoring reserve */
if (last_alloc >= s_index) {
as_len = last_alloc + 1 - s_index;
/*
* Iterate through chunk map computing size info.
* The first bit is overloaded to be a used flag.
* negative = free space, positive = allocated
*/
for (i = 0, p = chunk->map + s_index; i < as_len; i++, p++) {
alloc_sign = (*p & 1) ? 1 : -1;
alloc_sizes[i] = alloc_sign *
((p[1] & ~1) - (p[0] & ~1));
}
sort(alloc_sizes, as_len, sizeof(chunk->map[0]), cmpint, NULL);
/* Iterate through the unallocated fragements. */
for (i = 0, p = alloc_sizes; *p < 0 && i < as_len; i++, p++) {
sum_frag -= *p;
max_frag = max(max_frag, -1 * (*p));
}
cur_min_alloc = alloc_sizes[i];
cur_med_alloc = alloc_sizes[(i + as_len - 1) / 2];
cur_max_alloc = alloc_sizes[as_len - 1];
}
P("nr_alloc", chunk->nr_alloc);
P("max_alloc_size", chunk->max_alloc_size);
P("free_size", chunk->free_size);
P("contig_hint", chunk->contig_hint);
P("sum_frag", sum_frag);
P("max_frag", max_frag);
P("cur_min_alloc", cur_min_alloc);
P("cur_med_alloc", cur_med_alloc);
P("cur_max_alloc", cur_max_alloc);
seq_putc(m, '\n');
}
static int percpu_stats_show(struct seq_file *m, void *v)
{
struct pcpu_chunk *chunk;
int slot, max_map_used;
void *buffer;
alloc_buffer:
spin_lock_irq(&pcpu_lock);
max_map_used = find_max_map_used();
spin_unlock_irq(&pcpu_lock);
buffer = vmalloc(max_map_used * sizeof(pcpu_first_chunk->map[0]));
if (!buffer)
return -ENOMEM;
spin_lock_irq(&pcpu_lock);
/* if the buffer allocated earlier is too small */
if (max_map_used < find_max_map_used()) {
spin_unlock_irq(&pcpu_lock);
vfree(buffer);
goto alloc_buffer;
}
#define PL(X) \
seq_printf(m, " %-24s: %8lld\n", #X, (long long int)pcpu_stats_ai.X)
seq_printf(m,
"Percpu Memory Statistics\n"
"Allocation Info:\n"
"----------------------------------------\n");
PL(unit_size);
PL(static_size);
PL(reserved_size);
PL(dyn_size);
PL(atom_size);
PL(alloc_size);
seq_putc(m, '\n');
#undef PL
#define PU(X) \
seq_printf(m, " %-18s: %14llu\n", #X, (unsigned long long)pcpu_stats.X)
seq_printf(m,
"Global Stats:\n"
"----------------------------------------\n");
PU(nr_alloc);
PU(nr_dealloc);
PU(nr_cur_alloc);
PU(nr_max_alloc);
PU(nr_chunks);
PU(nr_max_chunks);
PU(min_alloc_size);
PU(max_alloc_size);
seq_putc(m, '\n');
#undef PU
seq_printf(m,
"Per Chunk Stats:\n"
"----------------------------------------\n");
if (pcpu_reserved_chunk) {
seq_puts(m, "Chunk: <- Reserved Chunk\n");
chunk_map_stats(m, pcpu_reserved_chunk, buffer);
}
for (slot = 0; slot < pcpu_nr_slots; slot++) {
list_for_each_entry(chunk, &pcpu_slot[slot], list) {
if (chunk == pcpu_first_chunk) {
seq_puts(m, "Chunk: <- First Chunk\n");
chunk_map_stats(m, chunk, buffer);
} else {
seq_puts(m, "Chunk:\n");
chunk_map_stats(m, chunk, buffer);
}
}
}
spin_unlock_irq(&pcpu_lock);
vfree(buffer);
return 0;
}
static int percpu_stats_open(struct inode *inode, struct file *filp)
{
return single_open(filp, percpu_stats_show, NULL);
}
static const struct file_operations percpu_stats_fops = {
.open = percpu_stats_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
static int __init init_percpu_stats_debugfs(void)
{
debugfs_create_file("percpu_stats", 0444, NULL, NULL,
&percpu_stats_fops);
return 0;
}
late_initcall(init_percpu_stats_debugfs);
......@@ -343,11 +343,16 @@ static struct pcpu_chunk *pcpu_create_chunk(void)
chunk->data = vms;
chunk->base_addr = vms[0]->addr - pcpu_group_offsets[0];
pcpu_stats_chunk_alloc();
return chunk;
}
static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
{
pcpu_stats_chunk_dealloc();
if (chunk && chunk->data)
pcpu_free_vm_areas(chunk->data, pcpu_nr_groups);
pcpu_free_chunk(chunk);
......
......@@ -657,6 +657,7 @@ static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme,
int *p;
lockdep_assert_held(&pcpu_lock);
pcpu_stats_area_dealloc(chunk);
freeme |= 1; /* we are searching for <given offset, in use> pair */
......@@ -721,6 +722,7 @@ static struct pcpu_chunk *pcpu_alloc_chunk(void)
chunk->map[0] = 0;
chunk->map[1] = pcpu_unit_size | 1;
chunk->map_used = 1;
chunk->has_reserved = false;
INIT_LIST_HEAD(&chunk->list);
INIT_LIST_HEAD(&chunk->map_extend_list);
......@@ -970,6 +972,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
goto restart;
area_found:
pcpu_stats_area_alloc(chunk, size);
spin_unlock_irqrestore(&pcpu_lock, flags);
/* populate if not all pages are already there */
......@@ -1642,6 +1645,8 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
pcpu_chunk_struct_size = sizeof(struct pcpu_chunk) +
BITS_TO_LONGS(pcpu_unit_pages) * sizeof(unsigned long);
pcpu_stats_save_ai(ai);
/*
* Allocate chunk slots. The additional last slot is for
* empty chunks.
......@@ -1685,6 +1690,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
if (schunk->free_size)
schunk->map[++schunk->map_used] = ai->static_size + schunk->free_size;
schunk->map[schunk->map_used] |= 1;
schunk->has_reserved = true;
/* init dynamic chunk if necessary */
if (dyn_size) {
......@@ -1703,6 +1709,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
dchunk->map[1] = pcpu_reserved_chunk_limit;
dchunk->map[2] = (pcpu_reserved_chunk_limit + dchunk->free_size) | 1;
dchunk->map_used = 2;
dchunk->has_reserved = true;
}
/* link the first chunk in */
......@@ -1711,6 +1718,8 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
pcpu_count_occupied_pages(pcpu_first_chunk, 1);
pcpu_chunk_relocate(pcpu_first_chunk, -1);
pcpu_stats_chunk_alloc();
/* we're done */
pcpu_base_addr = base_addr;
return 0;
......
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