Commit 94bfe85b authored by Yang Yang's avatar Yang Yang Committed by Andrew Morton
Browse files

mm/vmstat: add events for ksm cow 

Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want to
save memory, it's a tradeoff by suffering delay on ksm cow.  Users can get
to know how much memory ksm saved by reading
/sys/kernel/mm/ksm/pages_sharing, but they don't know what's the costs of
ksm cow, and this is important of some delay sensitive tasks.

So add ksm cow events to help users evaluate whether or how to use ksm. 
Also update Documentation/admin-guide/mm/ksm.rst with new added events.

Link: https://lkml.kernel.org/r/20220331035616.2390805-1-yang.yang29@zte.com.cn


Signed-off-by: default avatarYang Yang <yang.yang29@zte.com.cn>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarxu xin <xu.xin16@zte.com.cn>
Reviewed-by: default avatarRan Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Saravanan D <saravanand@fb.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 76093853

Documentation/admin-guide/mm/ksm.rst

+18 −0
Original line number Diff line number Diff line
@@ -184,6 +184,24 @@ The maximum possible ``pages_sharing/pages_shared`` ratio is limited by the 
``max_page_sharing`` tunable. To increase the ratio ``max_page_sharing`` must

be increased accordingly.



Monitoring KSM events

=====================



There are some counters in /proc/vmstat that may be used to monitor KSM events.

KSM might help save memory, it's a tradeoff by may suffering delay on KSM COW

or on swapping in copy. Those events could help users evaluate whether or how

to use KSM. For example, if cow_ksm increases too fast, user may decrease the

range of madvise(, , MADV_MERGEABLE).



cow_ksm

	is incremented every time a KSM page triggers copy on write (COW)

	when users try to write to a KSM page, we have to make a copy.



ksm_swpin_copy

	is incremented every time a KSM page is copied when swapping in

	note that KSM page might be copied when swapping in because do_swap_page()

	cannot do all the locking needed to reconstitute a cross-anon_vma KSM page.



--

Izik Eidus,

Hugh Dickins, 17 Nov 2009

include/linux/vm_event_item.h

+3 −0
Original line number Diff line number Diff line
@@ -133,6 +133,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, 
		KSM_SWPIN_COPY,

#endif

#endif

#ifdef CONFIG_KSM

		COW_KSM,

#endif

#ifdef CONFIG_X86

		DIRECT_MAP_LEVEL2_SPLIT,

		DIRECT_MAP_LEVEL3_SPLIT,

mm/memory.c

+4 −0
Original line number Diff line number Diff line
@@ -3331,6 +3331,10 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) 
	get_page(vmf->page);



	pte_unmap_unlock(vmf->pte, vmf->ptl);

#ifdef CONFIG_KSM

	if (PageKsm(vmf->page))

		count_vm_event(COW_KSM);

#endif

	return wp_page_copy(vmf);

}

mm/vmstat.c

+3 −0
Original line number Diff line number Diff line
@@ -1393,6 +1393,9 @@ const char * const vmstat_text[] = { 
	"ksm_swpin_copy",

#endif

#endif

#ifdef CONFIG_KSM

	"cow_ksm",

#endif

#ifdef CONFIG_X86

	"direct_map_level2_splits",

	"direct_map_level3_splits",