[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 <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins
Linus Torvalds
parent
65500d234e
commit
7be7a54699
166
mm/mremap.c
166
mm/mremap.c
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@ -22,40 +22,15 @@
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#include <asm/cacheflush.h>
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#include <asm/tlbflush.h>
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static pte_t *get_one_pte_map_nested(struct mm_struct *mm, unsigned long addr)
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{
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pgd_t *pgd;
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pud_t *pud;
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pmd_t *pmd;
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pte_t *pte = NULL;
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pgd = pgd_offset(mm, addr);
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if (pgd_none_or_clear_bad(pgd))
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goto end;
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pud = pud_offset(pgd, addr);
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if (pud_none_or_clear_bad(pud))
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goto end;
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pmd = pmd_offset(pud, addr);
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if (pmd_none_or_clear_bad(pmd))
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goto end;
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pte = pte_offset_map_nested(pmd, addr);
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if (pte_none(*pte)) {
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pte_unmap_nested(pte);
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pte = NULL;
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}
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end:
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return pte;
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}
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static pte_t *get_one_pte_map(struct mm_struct *mm, unsigned long addr)
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static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
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{
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pgd_t *pgd;
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pud_t *pud;
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pmd_t *pmd;
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/*
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* We don't need page_table_lock: we have mmap_sem exclusively.
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*/
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pgd = pgd_offset(mm, addr);
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if (pgd_none_or_clear_bad(pgd))
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return NULL;
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@ -68,35 +43,48 @@ static pte_t *get_one_pte_map(struct mm_struct *mm, unsigned long addr)
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if (pmd_none_or_clear_bad(pmd))
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return NULL;
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return pte_offset_map(pmd, addr);
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return pmd;
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}
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static inline pte_t *alloc_one_pte_map(struct mm_struct *mm, unsigned long addr)
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static pmd_t *alloc_new_pmd(struct mm_struct *mm, unsigned long addr)
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{
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pgd_t *pgd;
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pud_t *pud;
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pmd_t *pmd;
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pte_t *pte = NULL;
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pmd_t *pmd = NULL;
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pte_t *pte;
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/*
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* We do need page_table_lock: because allocators expect that.
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*/
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spin_lock(&mm->page_table_lock);
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pgd = pgd_offset(mm, addr);
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pud = pud_alloc(mm, pgd, addr);
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if (!pud)
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return NULL;
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goto out;
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pmd = pmd_alloc(mm, pud, addr);
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if (pmd)
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pte = pte_alloc_map(mm, pmd, addr);
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return pte;
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if (!pmd)
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goto out;
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pte = pte_alloc_map(mm, pmd, addr);
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if (!pte) {
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pmd = NULL;
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goto out;
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}
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pte_unmap(pte);
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out:
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spin_unlock(&mm->page_table_lock);
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return pmd;
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}
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static int
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move_one_page(struct vm_area_struct *vma, unsigned long old_addr,
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struct vm_area_struct *new_vma, unsigned long new_addr)
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static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
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unsigned long old_addr, unsigned long old_end,
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struct vm_area_struct *new_vma, pmd_t *new_pmd,
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unsigned long new_addr)
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{
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struct address_space *mapping = NULL;
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struct mm_struct *mm = vma->vm_mm;
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int error = 0;
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pte_t *src, *dst;
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pte_t *old_pte, *new_pte, pte;
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if (vma->vm_file) {
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/*
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@ -111,74 +99,62 @@ move_one_page(struct vm_area_struct *vma, unsigned long old_addr,
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new_vma->vm_truncate_count != vma->vm_truncate_count)
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new_vma->vm_truncate_count = 0;
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}
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spin_lock(&mm->page_table_lock);
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old_pte = pte_offset_map(old_pmd, old_addr);
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new_pte = pte_offset_map_nested(new_pmd, new_addr);
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src = get_one_pte_map_nested(mm, old_addr);
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if (src) {
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/*
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* Look to see whether alloc_one_pte_map needs to perform a
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* memory allocation. If it does then we need to drop the
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* atomic kmap
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*/
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dst = get_one_pte_map(mm, new_addr);
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if (unlikely(!dst)) {
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pte_unmap_nested(src);
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if (mapping)
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spin_unlock(&mapping->i_mmap_lock);
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dst = alloc_one_pte_map(mm, new_addr);
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if (mapping && !spin_trylock(&mapping->i_mmap_lock)) {
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spin_unlock(&mm->page_table_lock);
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spin_lock(&mapping->i_mmap_lock);
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spin_lock(&mm->page_table_lock);
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}
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src = get_one_pte_map_nested(mm, old_addr);
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}
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/*
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* Since alloc_one_pte_map can drop and re-acquire
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* page_table_lock, we should re-check the src entry...
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*/
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if (src) {
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if (dst) {
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pte_t pte;
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pte = ptep_clear_flush(vma, old_addr, src);
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/* ZERO_PAGE can be dependant on virtual addr */
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pte = move_pte(pte, new_vma->vm_page_prot,
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old_addr, new_addr);
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set_pte_at(mm, new_addr, dst, pte);
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} else
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error = -ENOMEM;
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pte_unmap_nested(src);
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}
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if (dst)
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pte_unmap(dst);
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for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
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new_pte++, new_addr += PAGE_SIZE) {
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if (pte_none(*old_pte))
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continue;
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pte = ptep_clear_flush(vma, old_addr, old_pte);
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/* ZERO_PAGE can be dependant on virtual addr */
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pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
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set_pte_at(mm, new_addr, new_pte, pte);
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}
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pte_unmap_nested(new_pte - 1);
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pte_unmap(old_pte - 1);
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spin_unlock(&mm->page_table_lock);
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if (mapping)
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spin_unlock(&mapping->i_mmap_lock);
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return error;
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}
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#define LATENCY_LIMIT (64 * PAGE_SIZE)
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static unsigned long move_page_tables(struct vm_area_struct *vma,
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unsigned long old_addr, struct vm_area_struct *new_vma,
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unsigned long new_addr, unsigned long len)
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{
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unsigned long offset;
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unsigned long extent, next, old_end;
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pmd_t *old_pmd, *new_pmd;
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flush_cache_range(vma, old_addr, old_addr + len);
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old_end = old_addr + len;
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flush_cache_range(vma, old_addr, old_end);
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/*
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* This is not the clever way to do this, but we're taking the
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* easy way out on the assumption that most remappings will be
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* only a few pages.. This also makes error recovery easier.
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*/
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for (offset = 0; offset < len; offset += PAGE_SIZE) {
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if (move_one_page(vma, old_addr + offset,
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new_vma, new_addr + offset) < 0)
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break;
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for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
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cond_resched();
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next = (old_addr + PMD_SIZE) & PMD_MASK;
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if (next - 1 > old_end)
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next = old_end;
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extent = next - old_addr;
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old_pmd = get_old_pmd(vma->vm_mm, old_addr);
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if (!old_pmd)
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continue;
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new_pmd = alloc_new_pmd(vma->vm_mm, new_addr);
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if (!new_pmd)
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break;
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next = (new_addr + PMD_SIZE) & PMD_MASK;
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if (extent > next - new_addr)
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extent = next - new_addr;
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if (extent > LATENCY_LIMIT)
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extent = LATENCY_LIMIT;
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move_ptes(vma, old_pmd, old_addr, old_addr + extent,
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new_vma, new_pmd, new_addr);
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}
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return offset;
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return len + old_addr - old_end; /* how much done */
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}
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static unsigned long move_vma(struct vm_area_struct *vma,
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