diff options
| -rw-r--r-- | mm/ksm.c | 108 |
1 files changed, 85 insertions, 23 deletions
@@ -294,10 +294,10 @@ static inline int in_stable_tree(struct rmap_item *rmap_item) * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. */ -static void break_ksm(struct vm_area_struct *vma, unsigned long addr) +static int break_ksm(struct vm_area_struct *vma, unsigned long addr) { struct page *page; - int ret; + int ret = 0; do { cond_resched(); @@ -310,9 +310,36 @@ static void break_ksm(struct vm_area_struct *vma, unsigned long addr) else ret = VM_FAULT_WRITE; put_page(page); - } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS))); - - /* Which leaves us looping there if VM_FAULT_OOM: hmmm... */ + } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM))); + /* + * We must loop because handle_mm_fault() may back out if there's + * any difficulty e.g. if pte accessed bit gets updated concurrently. + * + * VM_FAULT_WRITE is what we have been hoping for: it indicates that + * COW has been broken, even if the vma does not permit VM_WRITE; + * but note that a concurrent fault might break PageKsm for us. + * + * VM_FAULT_SIGBUS could occur if we race with truncation of the + * backing file, which also invalidates anonymous pages: that's + * okay, that truncation will have unmapped the PageKsm for us. + * + * VM_FAULT_OOM: at the time of writing (late July 2009), setting + * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the + * current task has TIF_MEMDIE set, and will be OOM killed on return + * to user; and ksmd, having no mm, would never be chosen for that. + * + * But if the mm is in a limited mem_cgroup, then the fault may fail + * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and + * even ksmd can fail in this way - though it's usually breaking ksm + * just to undo a merge it made a moment before, so unlikely to oom. + * + * That's a pity: we might therefore have more kernel pages allocated + * than we're counting as nodes in the stable tree; but ksm_do_scan + * will retry to break_cow on each pass, so should recover the page + * in due course. The important thing is to not let VM_MERGEABLE + * be cleared while any such pages might remain in the area. + */ + return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; } static void break_cow(struct mm_struct *mm, unsigned long addr) @@ -462,39 +489,61 @@ static void remove_trailing_rmap_items(struct mm_slot *mm_slot, * to the next pass of ksmd - consider, for example, how ksmd might be * in cmp_and_merge_page on one of the rmap_items we would be removing. */ -static void unmerge_ksm_pages(struct vm_area_struct *vma, - unsigned long start, unsigned long end) +static int unmerge_ksm_pages(struct vm_area_struct *vma, + unsigned long start, unsigned long end) { unsigned long addr; + int err = 0; - for (addr = start; addr < end; addr += PAGE_SIZE) - break_ksm(vma, addr); + for (addr = start; addr < end && !err; addr += PAGE_SIZE) { + if (signal_pending(current)) + err = -ERESTARTSYS; + else + err = break_ksm(vma, addr); + } + return err; } -static void unmerge_and_remove_all_rmap_items(void) +static int unmerge_and_remove_all_rmap_items(void) { struct mm_slot *mm_slot; struct mm_struct *mm; struct vm_area_struct *vma; + int err = 0; + + spin_lock(&ksm_mmlist_lock); + mm_slot = list_entry(ksm_mm_head.mm_list.next, + struct mm_slot, mm_list); + spin_unlock(&ksm_mmlist_lock); - list_for_each_entry(mm_slot, &ksm_mm_head.mm_list, mm_list) { + while (mm_slot != &ksm_mm_head) { mm = mm_slot->mm; down_read(&mm->mmap_sem); for (vma = mm->mmap; vma; vma = vma->vm_next) { if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) continue; - unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end); + err = unmerge_ksm_pages(vma, + vma->vm_start, vma->vm_end); + if (err) { + up_read(&mm->mmap_sem); + goto out; + } } remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next); up_read(&mm->mmap_sem); + + spin_lock(&ksm_mmlist_lock); + mm_slot = list_entry(mm_slot->mm_list.next, + struct mm_slot, mm_list); + spin_unlock(&ksm_mmlist_lock); } + ksm_scan.seqnr = 0; +out: spin_lock(&ksm_mmlist_lock); - if (ksm_scan.mm_slot != &ksm_mm_head) { - ksm_scan.mm_slot = &ksm_mm_head; - ksm_scan.seqnr++; - } + ksm_scan.mm_slot = &ksm_mm_head; spin_unlock(&ksm_mmlist_lock); + return err; } static void remove_mm_from_lists(struct mm_struct *mm) @@ -1051,6 +1100,8 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) /* * A ksm page might have got here by fork, but its other * references have already been removed from the stable tree. + * Or it might be left over from a break_ksm which failed + * when the mem_cgroup had reached its limit: try again now. */ if (PageKsm(page)) break_cow(rmap_item->mm, rmap_item->address); @@ -1286,6 +1337,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, unsigned long end, int advice, unsigned long *vm_flags) { struct mm_struct *mm = vma->vm_mm; + int err; switch (advice) { case MADV_MERGEABLE: @@ -1298,9 +1350,11 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, VM_MIXEDMAP | VM_SAO)) return 0; /* just ignore the advice */ - if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) - if (__ksm_enter(mm) < 0) - return -EAGAIN; + if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { + err = __ksm_enter(mm); + if (err) + return err; + } *vm_flags |= VM_MERGEABLE; break; @@ -1309,8 +1363,11 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, if (!(*vm_flags & VM_MERGEABLE)) return 0; /* just ignore the advice */ - if (vma->anon_vma) - unmerge_ksm_pages(vma, start, end); + if (vma->anon_vma) { + err = unmerge_ksm_pages(vma, start, end); + if (err) + return err; + } *vm_flags &= ~VM_MERGEABLE; break; @@ -1441,8 +1498,13 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, mutex_lock(&ksm_thread_mutex); if (ksm_run != flags) { ksm_run = flags; - if (flags & KSM_RUN_UNMERGE) - unmerge_and_remove_all_rmap_items(); + if (flags & KSM_RUN_UNMERGE) { + err = unmerge_and_remove_all_rmap_items(); + if (err) { + ksm_run = KSM_RUN_STOP; + count = err; + } + } } mutex_unlock(&ksm_thread_mutex); |