Commit 1a8e8430 authored by xu xin's avatar xu xin Committed by Andrew Morton
Browse files

ksm: consider KSM-placed zeropages when calculating KSM profit 

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: default avatarxu xin <xu.xin16@zte.com.cn>
Acked-by: default avatarDavid 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6080d19f

Documentation/admin-guide/mm/ksm.rst

+11 −7
Original line number Diff line number Diff line
@@ -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

mm/ksm.c

+2 −2
Original line number Diff line number Diff line
@@ -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);