On Fri, Jan 03, 2020 at 03:18:46PM +0800, Wei Yang wrote: >On Tue, Dec 24, 2019 at 06:28:56AM +0800, Wei Yang wrote: >>When page is not NULL, function is called by try_to_unmap_one() with >>TTU_SPLIT_HUGE_PMD set. There are two cases to call try_to_unmap_one() >>with TTU_SPLIT_HUGE_PMD set: >> >> * unmap_page() >> * shrink_page_list() >> >>In both case, the page passed to try_to_unmap_one() is PageHead() of the >>THP. If this page's mapping address in process is not HPAGE_PMD_SIZE >>aligned, this means the THP is not mapped as PMD THP in this process. >>This could happen when we do mremap() a PMD size range to an un-aligned >>address. >> >>Currently, this case is handled by following check in __split_huge_pmd() >>luckily. >> >> page != pmd_page(*pmd) >> >>This patch checks the address to skip some work. > >I am sorry to forget address Kirill's comment in 1st version. > >The first one is the performance difference after this change for a PTE >mappged THP. > >Here is the result:(in cycle) > > Before Patched > > 963 195 > 988 40 > 895 78 > >Average 948 104 > >So the change reduced 90% time for function split_huge_pmd_address(). > >For the 2nd comment, the vma check. Let me take a further look to analysis. > >Thanks for Kirill's suggestion. > For 2nd comment, check vma could hold huge page. You mean do this check ? vma->vm_start <= address && vma->vm_end >= address + HPAGE_PMD_SIZE This happens after munmap a partial of the THP range? After doing so, we can skip split_pmd for this case. >> >>Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> >> >>--- >>v2: move the check into split_huge_pmd_address(). >>--- >> mm/huge_memory.c | 16 ++++++++++++++++ >> 1 file changed, 16 insertions(+) >> >>diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>index 893fecd5daa4..2b9c2f412b32 100644 >>--- a/mm/huge_memory.c >>+++ b/mm/huge_memory.c >>@@ -2342,6 +2342,22 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, >> pud_t *pud; >> pmd_t *pmd; >> >>+ /* >>+ * When page is not NULL, function is called by try_to_unmap_one() >>+ * with TTU_SPLIT_HUGE_PMD set. There are two places set >>+ * TTU_SPLIT_HUGE_PMD >>+ * >>+ * unmap_page() >>+ * shrink_page_list() >>+ * >>+ * In both cases, the "page" here is the PageHead() of a THP. >>+ * >>+ * If the page is not a PMD mapped huge page, e.g. after mremap(), it >>+ * is not necessary to split it. >>+ */ >>+ if (page && !IS_ALIGNED(address, HPAGE_PMD_SIZE)) >>+ return; >>+ >> pgd = pgd_offset(vma->vm_mm, address); >> if (!pgd_present(*pgd)) >> return; >>-- >>2.17.1 > >-- >Wei Yang >Help you, Help me -- Wei Yang Help you, Help me
