[Pmem] Re: [PATCH] autonuma: reduce cache footprint when scanning page tables

From: Huang Ying <ying.huang(a)intel.com> ANBZ: #80 commit a818f5363a0eba04bcff986c64c919d3f44b8017 upstream 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(a)intel.com> Acked-by: Mel Gorman <mgorman(a)suse.de> Cc: Michal Hocko <mhocko(a)suse.com> Cc: Rik van Riel <riel(a)redhat.com> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Ingo Molnar <mingo(a)kernel.org> Cc: Dave Hansen <dave.hansen(a)linux.intel.com> Cc: Dan Williams <dan.j.williams(a)intel.com> Cc: Fengguang Wu <fengguang.wu(a)intel.com> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org> Signed-off-by: Baolin Wang <baolin.wang(a)linux.alibaba.com> --- mm/mprotect.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/mm/mprotect.c b/mm/mprotect.c index 6525e96..01681e3 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -84,6 +84,10 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, int nid; bool toptier; + /* Avoid TLB flush if possible */ + if (pte_protnone(oldpte)) + continue; + page = vm_normal_page(vma, addr, oldpte); if (!page || PageKsm(page)) continue; @@ -93,10 +97,6 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, page_mapcount(page) != 1) 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.