mm/vmstat: add event for ksm swapping in copy

When faults in from swap what used to be a KSM page and that page had been
swapped in before, system has to make a copy, and leaves remerging the
pages to a later pass of ksmd.

That is not good for performace, we'd better to reduce this kind of copy.
There are some ways to reduce it, for example lessen swappiness or
madvise(, , MADV_MERGEABLE) range.  So add this event to support doing
this tuning.  Just like this patch: "mm, THP, swap: add THP swapping out
fallback counting".

Link: https://lkml.kernel.org/r/20220113023839.758845-1-yang.yang29@zte.com.cn
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Reviewed-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Hugh Dickins <hughd@google.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Saravanan D <saravanand@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 7b2363388bfa29291f70e527db2f5edd2ffdc516..16a0a4fd000be0a62eaf5ac33cb66c95808dd59b 100644 (file)
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -129,6 +129,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #ifdef CONFIG_SWAP
                SWAP_RA,
                SWAP_RA_HIT,
+#ifdef CONFIG_KSM
+               KSM_SWPIN_COPY,
+#endif
 #endif
 #ifdef CONFIG_X86
                DIRECT_MAP_LEVEL2_SPLIT,

diff --git a/mm/ksm.c b/mm/ksm.c
index c20bd4d9a0d9ed00aa896deebadefc1ca4115dd4..4a7f8614e57d35765398a4c660d4c5d1b529bc44 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2595,6 +2595,9 @@ struct page *ksm_might_need_to_copy(struct page *page,
                SetPageDirty(new_page);
                __SetPageUptodate(new_page);
                __SetPageLocked(new_page);
+#ifdef CONFIG_SWAP
+               count_vm_event(KSM_SWPIN_COPY);
+#endif
        }
 
        return new_page;

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 846b670dd346a6bbee0d16ff9423ddaa4829e551..d5cc8d739fac107819bee88ea5c4312216a73f3a 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1388,6 +1388,9 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_SWAP
        "swap_ra",
        "swap_ra_hit",
+#ifdef CONFIG_KSM
+       "ksm_swpin_copy",
+#endif
 #endif
 #ifdef CONFIG_X86
        "direct_map_level2_splits",