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vmstat: kernel stack usage histogram

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As part of the dynamic kernel stack project, we need to know the amount of
data that can be saved by reducing the default kernel stack size [1].

Provide a kernel stack usage histogram to aid in optimizing kernel stack
sizes and minimizing memory waste in large-scale environments.  The
histogram divides stack usage into power-of-two buckets and reports the
results in /proc/vmstat.  This information is especially valuable in
environments with millions of machines, where even small optimizations can
have a significant impact.

The histogram data is presented in /proc/vmstat with entries like
"kstack_1k", "kstack_2k", and so on, indicating the number of threads that
exited with stack usage falling within each respective bucket.

Example outputs:
Intel:
$ grep kstack /proc/vmstat
kstack_1k 3
kstack_2k 188
kstack_4k 11391
kstack_8k 243
kstack_16k 0

ARM with 64K page_size:
$ grep kstack /proc/vmstat
kstack_1k 1
kstack_2k 340
kstack_4k 25212
kstack_8k 1659
kstack_16k 0
kstack_32k 0
kstack_64k 0

Note: once the dynamic kernel stack is implemented it will depend on the
implementation the usability of this feature: On hardware that supports
faults on kernel stacks, we will have other metrics that show the total
number of pages allocated for stacks.  On hardware where faults are not
supported, we will most likely have some optimization where only some
threads are extended, and for those, these metrics will still be very
useful.

[1] https://lwn.net/Articles/974367

Link: https://lkml.kernel.org/r/20240730150158.832783-3-pasha.tatashin@soleen.com
Link: https://lkml.kernel.org/r/20240724203322.2765486-3-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Kent Overstreet <kent.overstreet@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Li Zhijian <lizhijian@fujitsu.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Pasha Tatashin 2024-07-24 20:33:21 +00:00 committed by Andrew Morton
parent 9db298a439
commit c4a6fce856
3 changed files with 86 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
include/linux/vm_event_item.h
View File

@ -155,6 +155,30 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
VMA_LOCK_RETRY,
VMA_LOCK_MISS,
#endif
#ifdef CONFIG_DEBUG_STACK_USAGE
KSTACK_1K,
#if THREAD_SIZE > 1024
KSTACK_2K,
#endif
#if THREAD_SIZE > 2048
KSTACK_4K,
#endif
#if THREAD_SIZE > 4096
KSTACK_8K,
#endif
#if THREAD_SIZE > 8192
KSTACK_16K,
#endif
#if THREAD_SIZE > 16384
KSTACK_32K,
#endif
#if THREAD_SIZE > 32768
KSTACK_64K,
#endif
#if THREAD_SIZE > 65536
KSTACK_REST,
#endif
#endif /* CONFIG_DEBUG_STACK_USAGE */
NR_VM_EVENT_ITEMS
};

38
kernel/exit.c
View File

@ -778,6 +778,43 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
}
#ifdef CONFIG_DEBUG_STACK_USAGE
/* Count the maximum pages reached in kernel stacks */
static inline void kstack_histogram(unsigned long used_stack)
{
#ifdef CONFIG_VM_EVENT_COUNTERS
if (used_stack <= 1024)
count_vm_event(KSTACK_1K);
#if THREAD_SIZE > 1024
else if (used_stack <= 2048)
count_vm_event(KSTACK_2K);
#endif
#if THREAD_SIZE > 2048
else if (used_stack <= 4096)
count_vm_event(KSTACK_4K);
#endif
#if THREAD_SIZE > 4096
else if (used_stack <= 8192)
count_vm_event(KSTACK_8K);
#endif
#if THREAD_SIZE > 8192
else if (used_stack <= 16384)
count_vm_event(KSTACK_16K);
#endif
#if THREAD_SIZE > 16384
else if (used_stack <= 32768)
count_vm_event(KSTACK_32K);
#endif
#if THREAD_SIZE > 32768
else if (used_stack <= 65536)
count_vm_event(KSTACK_64K);
#endif
#if THREAD_SIZE > 65536
else
count_vm_event(KSTACK_REST);
#endif
#endif /* CONFIG_VM_EVENT_COUNTERS */
}
static void check_stack_usage(void)
{
static DEFINE_SPINLOCK(low_water_lock);
@ -785,6 +822,7 @@ static void check_stack_usage(void)
unsigned long free;
free = stack_not_used(current);
kstack_histogram(THREAD_SIZE - free);
if (free >= lowest_to_date)
return;

24
mm/vmstat.c
View File

@ -1436,6 +1436,30 @@ const char * const vmstat_text[] = {
"vma_lock_retry",
"vma_lock_miss",
#endif
#ifdef CONFIG_DEBUG_STACK_USAGE
"kstack_1k",
#if THREAD_SIZE > 1024
"kstack_2k",
#endif
#if THREAD_SIZE > 2048
"kstack_4k",
#endif
#if THREAD_SIZE > 4096
"kstack_8k",
#endif
#if THREAD_SIZE > 8192
"kstack_16k",
#endif
#if THREAD_SIZE > 16384
"kstack_32k",
#endif
#if THREAD_SIZE > 32768
"kstack_64k",
#endif
#if THREAD_SIZE > 65536
"kstack_rest",
#endif
#endif
#endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
};
#endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */