Messages in this thread Patch in this message | | | Date | Sat, 18 Feb 2012 14:19:13 +0800 | Subject | [PATCH] mm: hugetlb: break COW earlier for resv owner | From | Hillf Danton <> |
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When a process owning a MAP_PRIVATE mapping fails to COW, due to references held by a child and insufficient huge page pool, page is unmapped from the child process to guarantee the original mappers reliability, and the child may get SIGKILLed if it later faults.
With that guarantee, COW is broken earlier on behalf of owners, and they will go less page faults.
Signed-off-by: Hillf Danton <dhillf@gmail.com> ---
--- a/mm/hugetlb.c Tue Feb 14 20:10:46 2012 +++ b/mm/hugetlb.c Sat Feb 18 13:29:58 2012 @@ -2145,10 +2145,12 @@ int copy_hugetlb_page_range(struct mm_st struct page *ptepage; unsigned long addr; int cow; + int owner; struct hstate *h = hstate_vma(vma); unsigned long sz = huge_page_size(h);
cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; + owner = is_vma_resv_set(vma, HPAGE_RESV_OWNER);
for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) { src_pte = huge_pte_offset(src, addr); @@ -2164,10 +2166,19 @@ int copy_hugetlb_page_range(struct mm_st
spin_lock(&dst->page_table_lock); spin_lock_nested(&src->page_table_lock, SINGLE_DEPTH_NESTING); - if (!huge_pte_none(huge_ptep_get(src_pte))) { + entry = huge_ptep_get(src_pte); + if (!huge_pte_none(entry)) { if (cow) - huge_ptep_set_wrprotect(src, addr, src_pte); - entry = huge_ptep_get(src_pte); + if (owner) { + /* + * Break COW for resv owner to go less + * page faults later + */ + entry = huge_pte_wrprotect(entry); + } else { + huge_ptep_set_wrprotect(src, addr, src_pte); + entry = huge_ptep_get(src_pte); + } ptepage = pte_page(entry); get_page(ptepage); page_dup_rmap(ptepage); --
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