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ksm: consider KSM-placed zeropages when calculating KSM profit

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When use_zero_pages is enabled, the calculation of ksm profit is not
correct because ksm zero pages is not counted in.  So update the
calculation of KSM profit including the documentation.

Link: https://lkml.kernel.org/r/20230613030942.186041-1-yang.yang29@zte.com.cn
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: Jiang Xuexin <jiang.xuexin@zte.com.cn>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
xu xin 2023-06-13 11:09:42 +08:00 committed by Andrew Morton
parent 6080d19f07
commit 1a8e843057
2 changed files with 13 additions and 9 deletions
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18
Documentation/admin-guide/mm/ksm.rst
View File

@ -203,21 +203,25 @@ several times, which are unprofitable memory consumed.
1) How to determine whether KSM save memory or consume memory in system-wide
range? Here is a simple approximate calculation for reference::
general_profit =~ pages_sharing * sizeof(page) - (all_rmap_items) *
general_profit =~ ksm_saved_pages * sizeof(page) - (all_rmap_items) *
sizeof(rmap_item);
where all_rmap_items can be easily obtained by summing ``pages_sharing``,
``pages_shared``, ``pages_unshared`` and ``pages_volatile``.
where ksm_saved_pages equals to the sum of ``pages_sharing`` +
``ksm_zero_pages`` of the system, and all_rmap_items can be easily
obtained by summing ``pages_sharing``, ``pages_shared``, ``pages_unshared``
and ``pages_volatile``.
2) The KSM profit inner a single process can be similarly obtained by the
following approximate calculation::
process_profit =~ ksm_merging_pages * sizeof(page) -
process_profit =~ ksm_saved_pages * sizeof(page) -
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``. The process profit
is also shown in ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
where ksm_saved_pages equals to the sum of ``ksm_merging_pages`` and
``ksm_zero_pages``, both of which are shown under the directory
``/proc/<pid>/ksm_stat``, and ksm_rmap_items is also 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

4
mm/ksm.c
View File

@ -3092,7 +3092,7 @@ static void wait_while_offlining(void)
#ifdef CONFIG_PROC_FS
long ksm_process_profit(struct mm_struct *mm)
{
return mm->ksm_merging_pages * PAGE_SIZE -
return (long)(mm->ksm_merging_pages + mm->ksm_zero_pages) * PAGE_SIZE -
mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
}
#endif /* CONFIG_PROC_FS */
@ -3373,7 +3373,7 @@ static ssize_t general_profit_show(struct kobject *kobj,
{
long general_profit;
general_profit = ksm_pages_sharing * PAGE_SIZE -
general_profit = (ksm_pages_sharing + ksm_zero_pages) * PAGE_SIZE -
ksm_rmap_items * sizeof(struct ksm_rmap_item);
return sysfs_emit(buf, "%ld\n", general_profit);