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mm: add new KSM process and sysfs knobs

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This adds the general_profit KSM sysfs knob and the process profit metric
knobs to ksm_stat.

1) expose general_profit metric

   The documentation mentions a general profit metric, however this
   metric is not calculated.  In addition the formula depends on the size
   of internal structures, which makes it more difficult for an
   administrator to make the calculation.  Adding the metric for a better
   user experience.

2) document general_profit sysfs knob

3) calculate ksm process profit metric

   The ksm documentation mentions the process profit metric and how to
   calculate it.  This adds the calculation of the metric.

4) mm: expose ksm process profit metric in ksm_stat

   This exposes the ksm process profit metric in /proc/<pid>/ksm_stat.
   The documentation mentions the formula for the ksm process profit
   metric, however it does not calculate it.  In addition the formula
   depends on the size of internal structures.  So it makes sense to
   expose it.

5) document new procfs ksm knobs

Link: https://lkml.kernel.org/r/20230418051342.1919757-3-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Stefan Roesch 2023-04-17 22:13:41 -07:00 committed by Andrew Morton
parent d7597f59d1
commit d21077fbc2
5 changed files with 41 additions and 1 deletions
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8
Documentation/ABI/testing/sysfs-kernel-mm-ksm
View File

@ -51,3 +51,11 @@ Description: Control merging pages across different NUMA nodes.
When it is set to 0 only pages from the same node are merged,
otherwise pages from all nodes can be merged together (default).
What: /sys/kernel/mm/ksm/general_profit
Date: April 2023
KernelVersion: 6.4
Contact: Linux memory management mailing list <linux-mm@kvack.org>
Description: Measure how effective KSM is.
general_profit: how effective is KSM. The formula for the
calculation is in Documentation/admin-guide/mm/ksm.rst.

5
Documentation/admin-guide/mm/ksm.rst
View File

@ -157,6 +157,8 @@ stable_node_chains_prune_millisecs
The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
general_profit
how effective is KSM. The calculation is explained below.
pages_shared
how many shared pages are being used
pages_sharing
@ -207,7 +209,8 @@ several times, which are unprofitable memory consumed.
ksm_rmap_items * sizeof(rmap_item).
where ksm_merging_pages is shown under the directory ``/proc/<pid>/``,
and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``.
and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``. The process profit
is also shown in ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
From the perspective of application, a high ratio of ``ksm_rmap_items`` to
``ksm_merging_pages`` means a bad madvise-applied policy, so developers or

3
fs/proc/base.c
View File

@ -96,6 +96,7 @@
#include <linux/time_namespace.h>
#include <linux/resctrl.h>
#include <linux/cn_proc.h>
#include <linux/ksm.h>
#include <trace/events/oom.h>
#include "internal.h"
#include "fd.h"
@ -3207,6 +3208,8 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
mm = get_task_mm(task);
if (mm) {
seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items);
seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages);
seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm));
mmput(mm);
}

5
include/linux/ksm.h
View File

@ -68,6 +68,11 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
void collect_procs_ksm(struct page *page, struct list_head *to_kill,
int force_early);
#endif
#ifdef CONFIG_PROC_FS
long ksm_process_profit(struct mm_struct *);
#endif /* CONFIG_PROC_FS */
#else /* !CONFIG_KSM */
static inline void ksm_add_vma(struct vm_area_struct *vma)

21
mm/ksm.c
View File

@ -3007,6 +3007,14 @@ static void wait_while_offlining(void)
}
#endif /* CONFIG_MEMORY_HOTREMOVE */
#ifdef CONFIG_PROC_FS
long ksm_process_profit(struct mm_struct *mm)
{
return mm->ksm_merging_pages * PAGE_SIZE -
mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
}
#endif /* CONFIG_PROC_FS */
#ifdef CONFIG_SYSFS
/*
* This all compiles without CONFIG_SYSFS, but is a waste of space.
@ -3271,6 +3279,18 @@ static ssize_t pages_volatile_show(struct kobject *kobj,
}
KSM_ATTR_RO(pages_volatile);
static ssize_t general_profit_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
long general_profit;
general_profit = ksm_pages_sharing * PAGE_SIZE -
ksm_rmap_items * sizeof(struct ksm_rmap_item);
return sysfs_emit(buf, "%ld\n", general_profit);
}
KSM_ATTR_RO(general_profit);
static ssize_t stable_node_dups_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
@ -3335,6 +3355,7 @@ static struct attribute *ksm_attrs[] = {
&stable_node_dups_attr.attr,
&stable_node_chains_prune_millisecs_attr.attr,
&use_zero_pages_attr.attr,
&general_profit_attr.attr,
NULL,
};