From 7be7a546994f1222b2312fd348da14e16b6b7b42 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 29 Oct 2005 18:16:00 -0700 Subject: [PATCH] mm: move_page_tables by extents Speeding up mremap's moving of ptes has never been a priority, but the locking will get more complicated shortly, and is already too baroque. Scrap the current one-by-one moving, do an extent at a time: curtailed by end of src and dst pmds (have to use PMD_SIZE: the way pmd_addr_end gets elided doesn't match this usage), and by latency considerations. One nice property of the old method is lost: it never allocated a page table unless absolutely necessary, so you could free empty page tables by mremapping to and fro. Whereas this way, it allocates a dst table wherever there was a src table. I keep diving in to reinstate the old behaviour, then come out preferring not to clutter how it now is. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mremap.c | 168 ++++++++++++++++++++++++++---------------------------------- 1 file changed, 72 insertions(+), 96 deletions(-) (limited to 'mm/mremap.c') diff --git a/mm/mremap.c b/mm/mremap.c index 55df8f53e84..f4e56209850 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -22,40 +22,15 @@ #include #include -static pte_t *get_one_pte_map_nested(struct mm_struct *mm, unsigned long addr) -{ - pgd_t *pgd; - pud_t *pud; - pmd_t *pmd; - pte_t *pte = NULL; - - pgd = pgd_offset(mm, addr); - if (pgd_none_or_clear_bad(pgd)) - goto end; - - pud = pud_offset(pgd, addr); - if (pud_none_or_clear_bad(pud)) - goto end; - - pmd = pmd_offset(pud, addr); - if (pmd_none_or_clear_bad(pmd)) - goto end; - - pte = pte_offset_map_nested(pmd, addr); - if (pte_none(*pte)) { - pte_unmap_nested(pte); - pte = NULL; - } -end: - return pte; -} - -static pte_t *get_one_pte_map(struct mm_struct *mm, unsigned long addr) +static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; + /* + * We don't need page_table_lock: we have mmap_sem exclusively. + */ pgd = pgd_offset(mm, addr); if (pgd_none_or_clear_bad(pgd)) return NULL; @@ -68,35 +43,48 @@ static pte_t *get_one_pte_map(struct mm_struct *mm, unsigned long addr) if (pmd_none_or_clear_bad(pmd)) return NULL; - return pte_offset_map(pmd, addr); + return pmd; } -static inline pte_t *alloc_one_pte_map(struct mm_struct *mm, unsigned long addr) +static pmd_t *alloc_new_pmd(struct mm_struct *mm, unsigned long addr) { pgd_t *pgd; pud_t *pud; - pmd_t *pmd; - pte_t *pte = NULL; + pmd_t *pmd = NULL; + pte_t *pte; + /* + * We do need page_table_lock: because allocators expect that. + */ + spin_lock(&mm->page_table_lock); pgd = pgd_offset(mm, addr); - pud = pud_alloc(mm, pgd, addr); if (!pud) - return NULL; + goto out; + pmd = pmd_alloc(mm, pud, addr); - if (pmd) - pte = pte_alloc_map(mm, pmd, addr); - return pte; + if (!pmd) + goto out; + + pte = pte_alloc_map(mm, pmd, addr); + if (!pte) { + pmd = NULL; + goto out; + } + pte_unmap(pte); +out: + spin_unlock(&mm->page_table_lock); + return pmd; } -static int -move_one_page(struct vm_area_struct *vma, unsigned long old_addr, - struct vm_area_struct *new_vma, unsigned long new_addr) +static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, + unsigned long old_addr, unsigned long old_end, + struct vm_area_struct *new_vma, pmd_t *new_pmd, + unsigned long new_addr) { struct address_space *mapping = NULL; struct mm_struct *mm = vma->vm_mm; - int error = 0; - pte_t *src, *dst; + pte_t *old_pte, *new_pte, pte; if (vma->vm_file) { /* @@ -111,74 +99,62 @@ move_one_page(struct vm_area_struct *vma, unsigned long old_addr, new_vma->vm_truncate_count != vma->vm_truncate_count) new_vma->vm_truncate_count = 0; } - spin_lock(&mm->page_table_lock); - src = get_one_pte_map_nested(mm, old_addr); - if (src) { - /* - * Look to see whether alloc_one_pte_map needs to perform a - * memory allocation. If it does then we need to drop the - * atomic kmap - */ - dst = get_one_pte_map(mm, new_addr); - if (unlikely(!dst)) { - pte_unmap_nested(src); - if (mapping) - spin_unlock(&mapping->i_mmap_lock); - dst = alloc_one_pte_map(mm, new_addr); - if (mapping && !spin_trylock(&mapping->i_mmap_lock)) { - spin_unlock(&mm->page_table_lock); - spin_lock(&mapping->i_mmap_lock); - spin_lock(&mm->page_table_lock); - } - src = get_one_pte_map_nested(mm, old_addr); - } - /* - * Since alloc_one_pte_map can drop and re-acquire - * page_table_lock, we should re-check the src entry... - */ - if (src) { - if (dst) { - pte_t pte; - pte = ptep_clear_flush(vma, old_addr, src); - - /* ZERO_PAGE can be dependant on virtual addr */ - pte = move_pte(pte, new_vma->vm_page_prot, - old_addr, new_addr); - set_pte_at(mm, new_addr, dst, pte); - } else - error = -ENOMEM; - pte_unmap_nested(src); - } - if (dst) - pte_unmap(dst); + spin_lock(&mm->page_table_lock); + old_pte = pte_offset_map(old_pmd, old_addr); + new_pte = pte_offset_map_nested(new_pmd, new_addr); + + for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE, + new_pte++, new_addr += PAGE_SIZE) { + if (pte_none(*old_pte)) + continue; + pte = ptep_clear_flush(vma, old_addr, old_pte); + /* ZERO_PAGE can be dependant on virtual addr */ + pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr); + set_pte_at(mm, new_addr, new_pte, pte); } + + pte_unmap_nested(new_pte - 1); + pte_unmap(old_pte - 1); spin_unlock(&mm->page_table_lock); if (mapping) spin_unlock(&mapping->i_mmap_lock); - return error; } +#define LATENCY_LIMIT (64 * PAGE_SIZE) + static unsigned long move_page_tables(struct vm_area_struct *vma, unsigned long old_addr, struct vm_area_struct *new_vma, unsigned long new_addr, unsigned long len) { - unsigned long offset; + unsigned long extent, next, old_end; + pmd_t *old_pmd, *new_pmd; - flush_cache_range(vma, old_addr, old_addr + len); + old_end = old_addr + len; + flush_cache_range(vma, old_addr, old_end); - /* - * This is not the clever way to do this, but we're taking the - * easy way out on the assumption that most remappings will be - * only a few pages.. This also makes error recovery easier. - */ - for (offset = 0; offset < len; offset += PAGE_SIZE) { - if (move_one_page(vma, old_addr + offset, - new_vma, new_addr + offset) < 0) - break; + for (; old_addr < old_end; old_addr += extent, new_addr += extent) { cond_resched(); + next = (old_addr + PMD_SIZE) & PMD_MASK; + if (next - 1 > old_end) + next = old_end; + extent = next - old_addr; + old_pmd = get_old_pmd(vma->vm_mm, old_addr); + if (!old_pmd) + continue; + new_pmd = alloc_new_pmd(vma->vm_mm, new_addr); + if (!new_pmd) + break; + next = (new_addr + PMD_SIZE) & PMD_MASK; + if (extent > next - new_addr) + extent = next - new_addr; + if (extent > LATENCY_LIMIT) + extent = LATENCY_LIMIT; + move_ptes(vma, old_pmd, old_addr, old_addr + extent, + new_vma, new_pmd, new_addr); } - return offset; + + return len + old_addr - old_end; /* how much done */ } static unsigned long move_vma(struct vm_area_struct *vma, -- cgit v1.2.3