autonuma: reduce cache footprint when scanning page tables

In auto NUMA balancing page table scanning, if the pte_protnone() is
true, the PTE needs not to be changed because it's in target state
already.  So other checking on corresponding struct page is unnecessary
too.

So, if we check pte_protnone() firstly for each PTE, we can avoid
unnecessary struct page accessing, so that reduce the cache footprint of
NUMA balancing page table scanning.

In the performance test of pmbench memory accessing benchmark with 80:20
read/write ratio and normal access address distribution on a 2 socket
Intel server with Optance DC Persistent Memory, perf profiling shows
that the autonuma page table scanning time reduces from 1.23% to 0.97%
(that is, reduced 21%) with the patch.

Link: http://lkml.kernel.org/r/20191101075727.26683-3-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 7967825f6d3352b3b57ccd23018d461d41498b78..7a8e84f86831b4e4f2a8cdf535bf48fb9990979e 100644 (file)
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -80,6 +80,10 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                        if (prot_numa) {
                                struct page *page;
 
+                               /* Avoid TLB flush if possible */
+                               if (pte_protnone(oldpte))
+                                       continue;
+
                                page = vm_normal_page(vma, addr, oldpte);
                                if (!page || PageKsm(page))
                                        continue;
@@ -97,10 +101,6 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                                if (page_is_file_cache(page) && PageDirty(page))
                                        continue;
 
-                               /* Avoid TLB flush if possible */
-                               if (pte_protnone(oldpte))
-                                       continue;
-
                                /*
                                 * Don't mess with PTEs if page is already on the node
                                 * a single-threaded process is running on.