Messages in this thread Patch in this message | | | Date | Tue, 24 Jul 2007 10:38:55 +0200 | From | Ingo Molnar <> | Subject | [patch] mm: reduce pagetable-freeing latencies |
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the patch below has been tested in -rt for a long time - lets get it upstream please. It fixes some bad latencies on PREEMPT too.
Ingo
-----------------------> From: Hugh Dickins <hugh@veritas.com> Subject: mm: reduce pagetable-freeing latencies
2.6.15-rc1 moved the unlinking of a vma from its prio_tree and anon_vma into free_pgtables: so the vma is hidden from rmap and vmtruncate before freeing its page tables, allowing safe descent without page table lock. But free_pgtables is still called with preemption disabled, and Lee Revell has now detected high latency there.
The right fix will be to rework the mmu_gathering, not to need preemption disabled; but for now an ugly CONFIG_PREEMPT block in free_pgtables, to make an initial unlinking pass with preemption enabled - made uglier by CONFIG_IA64 definitions (only ia64 actually uses the start and end given to tlb_finish_mmu, and our floor and ceiling don't quite work for those). These CONFIG choices being to minimize the additional TLB flushing.
Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> --
mm/memory.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)
Index: linux-rt-rebase.q/mm/memory.c =================================================================== --- linux-rt-rebase.q.orig/mm/memory.c +++ linux-rt-rebase.q/mm/memory.c @@ -264,18 +264,48 @@ void free_pgd_range(struct mmu_gather ** flush_tlb_pgtables((*tlb)->mm, start, end); } +#ifdef CONFIG_IA64 +#define tlb_start_addr(tlb) (tlb)->start_addr +#define tlb_end_addr(tlb) (tlb)->end_addr +#else +#define tlb_start_addr(tlb) 0UL /* only ia64 really uses it */ +#define tlb_end_addr(tlb) 0UL /* only ia64 really uses it */ +#endif + void free_pgtables(struct mmu_gather **tlb, struct vm_area_struct *vma, unsigned long floor, unsigned long ceiling) { +#ifdef CONFIG_PREEMPT + struct vm_area_struct *unlink = vma; + int fullmm = (*tlb)->fullmm; + + if (!vma) /* Sometimes when exiting after an oops */ + return; + if (vma->vm_next) + tlb_finish_mmu(*tlb, tlb_start_addr(*tlb), tlb_end_addr(*tlb)); + /* + * Hide vma from rmap and vmtruncate before freeeing pgtables, + * with preemption enabled, except when unmapping just one area. + */ + while (unlink) { + anon_vma_unlink(unlink); + unlink_file_vma(unlink); + unlink = unlink->vm_next; + } + if (vma->vm_next) + *tlb = tlb_gather_mmu(vma->vm_mm, fullmm); +#endif while (vma) { struct vm_area_struct *next = vma->vm_next; unsigned long addr = vma->vm_start; +#ifndef CONFIG_PREEMPT /* * Hide vma from rmap and vmtruncate before freeing pgtables */ anon_vma_unlink(vma); unlink_file_vma(vma); +#endif if (is_vm_hugetlb_page(vma)) { hugetlb_free_pgd_range(tlb, addr, vma->vm_end, @@ -288,8 +318,10 @@ void free_pgtables(struct mmu_gather **t && !is_vm_hugetlb_page(next)) { vma = next; next = vma->vm_next; +#ifndef CONFIG_PREEMPT anon_vma_unlink(vma); unlink_file_vma(vma); +#endif } free_pgd_range(tlb, addr, vma->vm_end, floor, next? next->vm_start: ceiling); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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