Messages in this thread | | | Date | Thu, 20 Apr 2023 15:44:03 +0800 | Subject | Re: [PATCH] mm,unmap: avoid flushing TLB in batch if PTE is inaccessible | From | haoxin <> |
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在 2023/4/10 下午3:52, Huang Ying 写道: > 0Day/LKP reported a performance regression for commit > 7e12beb8ca2a ("migrate_pages: batch flushing TLB"). In the commit, the > TLB flushing during page migration is batched. So, in > try_to_migrate_one(), ptep_clear_flush() is replaced with > set_tlb_ubc_flush_pending(). In further investigation, it is found > that the TLB flushing can be avoided in ptep_clear_flush() if the PTE > is inaccessible. In fact, we can optimize in similar way for the > batched TLB flushing too to improve the performance. > > So in this patch, we check pte_accessible() before > set_tlb_ubc_flush_pending() in try_to_unmap/migrate_one(). Tests show > that the benchmark score of the anon-cow-rand-mt test case of > vm-scalability test suite can improve up to 2.1% with the patch on a > Intel server machine. The TLB flushing IPI can reduce up to 44.3%. > > Link: https://lore.kernel.org/oe-lkp/202303192325.ecbaf968-yujie.liu@intel.com > Link: https://lore.kernel.org/oe-lkp/ab92aaddf1b52ede15e2c608696c36765a2602c1.camel@intel.com/ > Fixes: 7e12beb8ca2a ("migrate_pages: batch flushing TLB") > Reported-by: kernel test robot <yujie.liu@intel.com> > Signed-off-by: "Huang, Ying" <ying.huang@intel.com> > Cc: Nadav Amit <namit@vmware.com> > Cc: Mel Gorman <mgorman@techsingularity.net> > Cc: Hugh Dickins <hughd@google.com> > Cc: Matthew Wilcox (Oracle) <willy@infradead.org> > Cc: David Hildenbrand <david@redhat.com> > --- > mm/rmap.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index 8632e02661ac..3c7c43642d7c 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1582,7 +1582,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > */ > pteval = ptep_get_and_clear(mm, address, pvmw.pte); > > - set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); > + if (pte_accessible(mm, pteval)) > + set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); > } else { > pteval = ptep_clear_flush(vma, address, pvmw.pte); > } > @@ -1963,7 +1964,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > */ > pteval = ptep_get_and_clear(mm, address, pvmw.pte); > > - set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); > + if (pte_accessible(mm, pteval)) > + set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
Just a advice, can you put pte_accessible() into set_tlb_ubc_flush_pendin(), just like ptep_clear_flush(); so that we no need to add if (pte_accessible()) in per place
where call set_tlb_ubc_flush_pending();
> } else { > pteval = ptep_clear_flush(vma, address, pvmw.pte); > }
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