From 7b6efc2bc4f19952b25ebf9b236e5ac43cd386c2 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Mon, 31 Oct 2011 17:08:26 -0700 Subject: [PATCH] mremap: avoid sending one IPI per page This replaces ptep_clear_flush() with ptep_get_and_clear() and a single flush_tlb_range() at the end of the loop, to avoid sending one IPI for each page. The mmu_notifier_invalidate_range_start/end section is enlarged accordingly but this is not going to fundamentally change things. It was more by accident that the region under mremap was for the most part still available for secondary MMUs: the primary MMU was never allowed to reliably access that region for the duration of the mremap (modulo trapping SIGSEGV on the old address range which sounds unpractical and flakey). If users wants secondary MMUs not to lose access to a large region under mremap they should reduce the mremap size accordingly in userland and run multiple calls. Overall this will run faster so it's actually going to reduce the time the region is under mremap for the primary MMU which should provide a net benefit to apps. For KVM this is a noop because the guest physical memory is never mremapped, there's just no point it ever moving it while guest runs. One target of this optimization is JVM GC (so unrelated to the mmu notifier logic). Signed-off-by: Andrea Arcangeli Acked-by: Johannes Weiner Acked-by: Mel Gorman Acked-by: Rik van Riel Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mremap.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index 195e866568e0..a184f3732e1e 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -80,11 +80,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, struct mm_struct *mm = vma->vm_mm; pte_t *old_pte, *new_pte, pte; spinlock_t *old_ptl, *new_ptl; - unsigned long old_start; - old_start = old_addr; - mmu_notifier_invalidate_range_start(vma->vm_mm, - old_start, old_end); if (vma->vm_file) { /* * Subtle point from Rajesh Venkatasubramanian: before @@ -111,7 +107,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, new_pte++, new_addr += PAGE_SIZE) { if (pte_none(*old_pte)) continue; - pte = ptep_clear_flush(vma, old_addr, old_pte); + pte = ptep_get_and_clear(mm, old_addr, old_pte); pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr); set_pte_at(mm, new_addr, new_pte, pte); } @@ -123,7 +119,6 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, pte_unmap_unlock(old_pte - 1, old_ptl); if (mapping) mutex_unlock(&mapping->i_mmap_mutex); - mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end); } #define LATENCY_LIMIT (64 * PAGE_SIZE) @@ -134,10 +129,13 @@ unsigned long move_page_tables(struct vm_area_struct *vma, { unsigned long extent, next, old_end; pmd_t *old_pmd, *new_pmd; + bool need_flush = false; old_end = old_addr + len; flush_cache_range(vma, old_addr, old_end); + mmu_notifier_invalidate_range_start(vma->vm_mm, old_addr, old_end); + for (; old_addr < old_end; old_addr += extent, new_addr += extent) { cond_resched(); next = (old_addr + PMD_SIZE) & PMD_MASK; @@ -158,7 +156,12 @@ unsigned long move_page_tables(struct vm_area_struct *vma, extent = LATENCY_LIMIT; move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma, new_pmd, new_addr); + need_flush = true; } + if (likely(need_flush)) + flush_tlb_range(vma, old_end-len, old_addr); + + mmu_notifier_invalidate_range_end(vma->vm_mm, old_end-len, old_end); return len + old_addr - old_end; /* how much done */ } -- 2.30.2