Hugh says: "The only significant loser, I think, would be page reclaim (when concurrent with truncation): could spin for a long time waiting for the i_mmap_mutex it expects would soon be dropped? " Counter points: - cpu contention makes the spin stop (need_resched()) - zap pages should be freeing pages at a higher rate than reclaim ever can - shouldn't hold up reclaim more than lock_page() would I think the simplification of the truncate code is definately worth it. Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> --- include/linux/fs.h | 1 include/linux/mm.h | 2 include/linux/mm_types.h | 1 kernel/fork.c | 1 mm/memory.c | 193 ++++++----------------------------------------- mm/mmap.c | 13 --- mm/mremap.c | 3 7 files changed, 27 insertions(+), 187 deletions(-) Index: linux-2.6/include/linux/mm.h =================================================================== --- linux-2.6.orig/include/linux/mm.h +++ linux-2.6/include/linux/mm.h @@ -878,8 +878,6 @@ struct zap_details { struct address_space *check_mapping; /* Check page->mapping if set */ pgoff_t first_index; /* Lowest page->index to unmap */ pgoff_t last_index; /* Highest page->index to unmap */ - spinlock_t *i_mmap_lock; /* For unmap_mapping_range: */ - unsigned long truncate_count; /* Compare vm_truncate_count */ }; struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, Index: linux-2.6/mm/memory.c =================================================================== --- linux-2.6.orig/mm/memory.c +++ linux-2.6/mm/memory.c @@ -986,13 +986,13 @@ int copy_page_range(struct mm_struct *ds static unsigned long zap_pte_range(struct mmu_gather *tlb, struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr, unsigned long end, - long *zap_work, struct zap_details *details) + struct zap_details *details) { struct mm_struct *mm = tlb->mm; int need_flush = 0; - pte_t *pte; - spinlock_t *ptl; int rss[NR_MM_COUNTERS]; + spinlock_t *ptl; + pte_t *pte; init_rss_vec(rss); again: @@ -1001,12 +1001,9 @@ static unsigned long zap_pte_range(struc do { pte_t ptent = *pte; if (pte_none(ptent)) { - (*zap_work)--; continue; } - (*zap_work) -= PAGE_SIZE; - if (pte_present(ptent)) { struct page *page; @@ -1073,8 +1070,7 @@ static unsigned long zap_pte_range(struc print_bad_pte(vma, addr, ptent, NULL); } pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); - } while (pte++, addr += PAGE_SIZE, - (addr != end && *zap_work > 0 && !need_flush)); + } while (pte++, addr += PAGE_SIZE, (addr != end && !need_flush)); add_mm_rss_vec(mm, rss); arch_leave_lazy_mmu_mode(); @@ -1093,7 +1089,7 @@ static unsigned long zap_pte_range(struc static inline unsigned long zap_pmd_range(struct mmu_gather *tlb, struct vm_area_struct *vma, pud_t *pud, unsigned long addr, unsigned long end, - long *zap_work, struct zap_details *details) + struct zap_details *details) { pmd_t *pmd; unsigned long next; @@ -1105,19 +1101,15 @@ static inline unsigned long zap_pmd_rang if (next-addr != HPAGE_PMD_SIZE) { VM_BUG_ON(!rwsem_is_locked(&tlb->mm->mmap_sem)); split_huge_page_pmd(vma->vm_mm, pmd); - } else if (zap_huge_pmd(tlb, vma, pmd)) { - (*zap_work)--; + } else if (zap_huge_pmd(tlb, vma, pmd)) continue; - } /* fall through */ } - if (pmd_none_or_clear_bad(pmd)) { - (*zap_work)--; + if (pmd_none_or_clear_bad(pmd)) continue; - } - next = zap_pte_range(tlb, vma, pmd, addr, next, - zap_work, details); - } while (pmd++, addr = next, (addr != end && *zap_work > 0)); + next = zap_pte_range(tlb, vma, pmd, addr, next, details); + cond_resched(); + } while (pmd++, addr = next, addr != end); return addr; } @@ -1125,7 +1117,7 @@ static inline unsigned long zap_pmd_rang static inline unsigned long zap_pud_range(struct mmu_gather *tlb, struct vm_area_struct *vma, pgd_t *pgd, unsigned long addr, unsigned long end, - long *zap_work, struct zap_details *details) + struct zap_details *details) { pud_t *pud; unsigned long next; @@ -1133,13 +1125,10 @@ static inline unsigned long zap_pud_rang pud = pud_offset(pgd, addr); do { next = pud_addr_end(addr, end); - if (pud_none_or_clear_bad(pud)) { - (*zap_work)--; + if (pud_none_or_clear_bad(pud)) continue; - } - next = zap_pmd_range(tlb, vma, pud, addr, next, - zap_work, details); - } while (pud++, addr = next, (addr != end && *zap_work > 0)); + next = zap_pmd_range(tlb, vma, pud, addr, next, details); + } while (pud++, addr = next, addr != end); return addr; } @@ -1147,7 +1136,7 @@ static inline unsigned long zap_pud_rang static unsigned long unmap_page_range(struct mmu_gather *tlb, struct vm_area_struct *vma, unsigned long addr, unsigned long end, - long *zap_work, struct zap_details *details) + struct zap_details *details) { pgd_t *pgd; unsigned long next; @@ -1161,13 +1150,10 @@ static unsigned long unmap_page_range(st pgd = pgd_offset(vma->vm_mm, addr); do { next = pgd_addr_end(addr, end); - if (pgd_none_or_clear_bad(pgd)) { - (*zap_work)--; + if (pgd_none_or_clear_bad(pgd)) continue; - } - next = zap_pud_range(tlb, vma, pgd, addr, next, - zap_work, details); - } while (pgd++, addr = next, (addr != end && *zap_work > 0)); + next = zap_pud_range(tlb, vma, pgd, addr, next, details); + } while (pgd++, addr = next, addr != end); tlb_end_vma(tlb, vma); mem_cgroup_uncharge_end(); @@ -1212,9 +1198,7 @@ unsigned long unmap_vmas(struct mmu_gath unsigned long end_addr, unsigned long *nr_accounted, struct zap_details *details) { - long zap_work = ZAP_BLOCK_SIZE; unsigned long start = start_addr; - spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL; struct mm_struct *mm = vma->vm_mm; mmu_notifier_invalidate_range_start(mm, start_addr, end_addr); @@ -1247,33 +1231,15 @@ unsigned long unmap_vmas(struct mmu_gath * Since no pte has actually been setup, it is * safe to do nothing in this case. */ - if (vma->vm_file) { + if (vma->vm_file) unmap_hugepage_range(vma, start, end, NULL); - zap_work -= (end - start) / - pages_per_huge_page(hstate_vma(vma)); - } start = end; } else - start = unmap_page_range(tlb, vma, - start, end, &zap_work, details); - - if (zap_work > 0) { - BUG_ON(start != end); - break; - } - - if (need_resched() || - (i_mmap_lock && spin_needbreak(i_mmap_lock))) { - if (i_mmap_lock) - goto out; - cond_resched(); - } - - zap_work = ZAP_BLOCK_SIZE; + start = unmap_page_range(tlb, vma, start, end, details); } } -out: + mmu_notifier_invalidate_range_end(mm, start_addr, end_addr); return start; /* which is now the end (or restart) address */ } @@ -2535,96 +2501,11 @@ static int do_wp_page(struct mm_struct * return ret; } -/* - * Helper functions for unmap_mapping_range(). - * - * __ Notes on dropping i_mmap_lock to reduce latency while unmapping __ - * - * We have to restart searching the prio_tree whenever we drop the lock, - * since the iterator is only valid while the lock is held, and anyway - * a later vma might be split and reinserted earlier while lock dropped. - * - * The list of nonlinear vmas could be handled more efficiently, using - * a placeholder, but handle it in the same way until a need is shown. - * It is important to search the prio_tree before nonlinear list: a vma - * may become nonlinear and be shifted from prio_tree to nonlinear list - * while the lock is dropped; but never shifted from list to prio_tree. - * - * In order to make forward progress despite restarting the search, - * vm_truncate_count is used to mark a vma as now dealt with, so we can - * quickly skip it next time around. Since the prio_tree search only - * shows us those vmas affected by unmapping the range in question, we - * can't efficiently keep all vmas in step with mapping->truncate_count: - * so instead reset them all whenever it wraps back to 0 (then go to 1). - * mapping->truncate_count and vma->vm_truncate_count are protected by - * i_mmap_lock. - * - * In order to make forward progress despite repeatedly restarting some - * large vma, note the restart_addr from unmap_vmas when it breaks out: - * and restart from that address when we reach that vma again. It might - * have been split or merged, shrunk or extended, but never shifted: so - * restart_addr remains valid so long as it remains in the vma's range. - * unmap_mapping_range forces truncate_count to leap over page-aligned - * values so we can save vma's restart_addr in its truncate_count field. - */ -#define is_restart_addr(truncate_count) (!((truncate_count) & ~PAGE_MASK)) - -static void reset_vma_truncate_counts(struct address_space *mapping) -{ - struct vm_area_struct *vma; - struct prio_tree_iter iter; - - vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, 0, ULONG_MAX) - vma->vm_truncate_count = 0; - list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) - vma->vm_truncate_count = 0; -} - -static int unmap_mapping_range_vma(struct vm_area_struct *vma, +static void unmap_mapping_range_vma(struct vm_area_struct *vma, unsigned long start_addr, unsigned long end_addr, struct zap_details *details) { - unsigned long restart_addr; - int need_break; - - /* - * files that support invalidating or truncating portions of the - * file from under mmaped areas must have their ->fault function - * return a locked page (and set VM_FAULT_LOCKED in the return). - * This provides synchronisation against concurrent unmapping here. - */ - -again: - restart_addr = vma->vm_truncate_count; - if (is_restart_addr(restart_addr) && start_addr < restart_addr) { - start_addr = restart_addr; - if (start_addr >= end_addr) { - /* Top of vma has been split off since last time */ - vma->vm_truncate_count = details->truncate_count; - return 0; - } - } - - restart_addr = zap_page_range(vma, start_addr, - end_addr - start_addr, details); - need_break = need_resched() || spin_needbreak(details->i_mmap_lock); - - if (restart_addr >= end_addr) { - /* We have now completed this vma: mark it so */ - vma->vm_truncate_count = details->truncate_count; - if (!need_break) - return 0; - } else { - /* Note restart_addr in vma's truncate_count field */ - vma->vm_truncate_count = restart_addr; - if (!need_break) - goto again; - } - - spin_unlock(details->i_mmap_lock); - cond_resched(); - spin_lock(details->i_mmap_lock); - return -EINTR; + zap_page_range(vma, start_addr, end_addr - start_addr, details); } static inline void unmap_mapping_range_tree(struct prio_tree_root *root, @@ -2634,12 +2515,8 @@ static inline void unmap_mapping_range_t struct prio_tree_iter iter; pgoff_t vba, vea, zba, zea; -restart: vma_prio_tree_foreach(vma, &iter, root, details->first_index, details->last_index) { - /* Skip quickly over those we have already dealt with */ - if (vma->vm_truncate_count == details->truncate_count) - continue; vba = vma->vm_pgoff; vea = vba + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) - 1; @@ -2651,11 +2528,10 @@ static inline void unmap_mapping_range_t if (zea > vea) zea = vea; - if (unmap_mapping_range_vma(vma, + unmap_mapping_range_vma(vma, ((zba - vba) << PAGE_SHIFT) + vma->vm_start, ((zea - vba + 1) << PAGE_SHIFT) + vma->vm_start, - details) < 0) - goto restart; + details); } } @@ -2670,15 +2546,9 @@ static inline void unmap_mapping_range_l * across *all* the pages in each nonlinear VMA, not just the pages * whose virtual address lies outside the file truncation point. */ -restart: list_for_each_entry(vma, head, shared.vm_set.list) { - /* Skip quickly over those we have already dealt with */ - if (vma->vm_truncate_count == details->truncate_count) - continue; details->nonlinear_vma = vma; - if (unmap_mapping_range_vma(vma, vma->vm_start, - vma->vm_end, details) < 0) - goto restart; + unmap_mapping_range_vma(vma, vma->vm_start, vma->vm_end, details); } } @@ -2717,19 +2587,8 @@ void unmap_mapping_range(struct address_ details.last_index = hba + hlen - 1; if (details.last_index < details.first_index) details.last_index = ULONG_MAX; - details.i_mmap_lock = &mapping->i_mmap_lock; spin_lock(&mapping->i_mmap_lock); - - /* Protect against endless unmapping loops */ - mapping->truncate_count++; - if (unlikely(is_restart_addr(mapping->truncate_count))) { - if (mapping->truncate_count == 0) - reset_vma_truncate_counts(mapping); - mapping->truncate_count++; - } - details.truncate_count = mapping->truncate_count; - if (unlikely(!prio_tree_empty(&mapping->i_mmap))) unmap_mapping_range_tree(&mapping->i_mmap, &details); if (unlikely(!list_empty(&mapping->i_mmap_nonlinear))) Index: linux-2.6/include/linux/fs.h =================================================================== --- linux-2.6.orig/include/linux/fs.h +++ linux-2.6/include/linux/fs.h @@ -640,7 +640,6 @@ struct address_space { struct prio_tree_root i_mmap; /* tree of private and shared mappings */ struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */ spinlock_t i_mmap_lock; /* protect tree, count, list */ - unsigned int truncate_count; /* Cover race condition with truncate */ unsigned long nrpages; /* number of total pages */ pgoff_t writeback_index;/* writeback starts here */ const struct address_space_operations *a_ops; /* methods */ Index: linux-2.6/include/linux/mm_types.h =================================================================== --- linux-2.6.orig/include/linux/mm_types.h +++ linux-2.6/include/linux/mm_types.h @@ -175,7 +175,6 @@ struct vm_area_struct { units, *not* PAGE_CACHE_SIZE */ struct file * vm_file; /* File we map to (can be NULL). */ void * vm_private_data; /* was vm_pte (shared mem) */ - unsigned long vm_truncate_count;/* truncate_count or restart_addr */ #ifndef CONFIG_MMU struct vm_region *vm_region; /* NOMMU mapping region */ Index: linux-2.6/kernel/fork.c =================================================================== --- linux-2.6.orig/kernel/fork.c +++ linux-2.6/kernel/fork.c @@ -379,7 +379,6 @@ static int dup_mmap(struct mm_struct *mm spin_lock(&mapping->i_mmap_lock); if (tmp->vm_flags & VM_SHARED) mapping->i_mmap_writable++; - tmp->vm_truncate_count = mpnt->vm_truncate_count; flush_dcache_mmap_lock(mapping); /* insert tmp into the share list, just after mpnt */ vma_prio_tree_add(tmp, mpnt); Index: linux-2.6/mm/mmap.c =================================================================== --- linux-2.6.orig/mm/mmap.c +++ linux-2.6/mm/mmap.c @@ -464,10 +464,8 @@ static void vma_link(struct mm_struct *m if (vma->vm_file) mapping = vma->vm_file->f_mapping; - if (mapping) { + if (mapping) spin_lock(&mapping->i_mmap_lock); - vma->vm_truncate_count = mapping->truncate_count; - } __vma_link(mm, vma, prev, rb_link, rb_parent); __vma_link_file(vma); @@ -577,16 +575,7 @@ again: remove_next = 1 + (end > next-> if (!(vma->vm_flags & VM_NONLINEAR)) root = &mapping->i_mmap; spin_lock(&mapping->i_mmap_lock); - if (importer && - vma->vm_truncate_count != next->vm_truncate_count) { - /* - * unmap_mapping_range might be in progress: - * ensure that the expanding vma is rescanned. - */ - importer->vm_truncate_count = 0; - } if (insert) { - insert->vm_truncate_count = vma->vm_truncate_count; /* * Put into prio_tree now, so instantiated pages * are visible to arm/parisc __flush_dcache_page Index: linux-2.6/mm/mremap.c =================================================================== --- linux-2.6.orig/mm/mremap.c +++ linux-2.6/mm/mremap.c @@ -94,9 +94,6 @@ static void move_ptes(struct vm_area_str */ mapping = vma->vm_file->f_mapping; spin_lock(&mapping->i_mmap_lock); - if (new_vma->vm_truncate_count && - new_vma->vm_truncate_count != vma->vm_truncate_count) - new_vma->vm_truncate_count = 0; } /* -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . 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