mm: reduce rmap overhead for ex-KSM page copies created on swap faults

When ex-KSM pages are faulted from swap cache, the fault handler is not
capable of re-establishing anon_vma-spanning KSM pages.  In this case, a
copy of the page is created instead, just like during a COW break.

These freshly made copies are known to be exclusive to the faulting VMA
and there is no reason to go look for this page in parent and sibling
processes during rmap operations.

Use page_add_new_anon_rmap() for these copies.  This also puts them on
the proper LRU lists and marks them SwapBacked, so we can get rid of
doing this ad-hoc in the KSM copy code.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 4 insertions, 7 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 51573858938d..e1f1f278075f 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1590,13 +1590,7 @@ struct page *ksm_does_need_to_copy(struct page *page,
 
                 SetPageDirty(new_page);
                 __SetPageUptodate(new_page);
-                SetPageSwapBacked(new_page);
                 __set_page_locked(new_page);
-
-                if (!mlocked_vma_newpage(vma, new_page))
-                        lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
-                else
-                        add_page_to_unevictable_list(new_page);
         }
 
         return new_page;
diff --git a/mm/memory.c b/mm/memory.c
index bb1369f7b9b4..0abd07097ec6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3044,7 +3044,10 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         }
         flush_icache_page(vma, page);
         set_pte_at(mm, address, page_table, pte);
-        do_page_add_anon_rmap(page, vma, address, exclusive);
+        if (swapcache) /* ksm created a completely new copy */
+                page_add_new_anon_rmap(page, vma, address);
+        else
+                do_page_add_anon_rmap(page, vma, address, exclusive);
         /* It's better to call commit-charge after rmap is established */
         mem_cgroup_commit_charge_swapin(page, ptr);