From: Yang Yang <yang.yang29@zte.com.cn>
Date: Fri, 29 Apr 2022 06:16:16 +0000 (-0700)
Subject: mm/vmstat: add events for ksm cow
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=94bfe85bde18a99612bb5d0ce348643c2d352836;p=linux.git

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: Yang Yang <yang.yang29@zte.com.cn>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: xu xin <xu.xin16@zte.com.cn>
Reviewed-by: Ran 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: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index 97d816791acae..b244f0202a036 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -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
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 16a0a4fd000be..e83967e4c20ea 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -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,
diff --git a/mm/memory.c b/mm/memory.c
index 8895dd2f22558..e873a61431815 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3331,6 +3331,10 @@ copy:
 	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);
 }
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index f2d0dec1062d5..b94a2e4723ff1 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -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",