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ksm: distribute remove_mm_from_lists
Do some housekeeping in ksm.c, to help make the next patch easier to understand: remove the function remove_mm_from_lists, distributing its code to its callsites scan_get_next_rmap_item and __ksm_exit. That turns out to be a win in scan_get_next_rmap_item: move its remove_trailing_rmap_items and cursor advancement up, and it becomes simpler than before. __ksm_exit becomes messier, but will change again; and moving its remove_trailing_rmap_items up lets us strengthen the unstable tree item's age condition in remove_rmap_item_from_tree. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Acked-by: Izik Eidus <ieidus@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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parent
d952b79136
commit
cd551f9751
97
mm/ksm.c
97
mm/ksm.c
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@ -444,14 +444,9 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
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* But __ksm_exit has to be careful: do the rb_erase
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* if it's interrupting a scan, and this rmap_item was
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* inserted by this scan rather than left from before.
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*
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* Because of the case in which remove_mm_from_lists
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* increments seqnr before removing rmaps, unstable_nr
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* may even be 2 behind seqnr, but should never be
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* further behind. Yes, I did have trouble with this!
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*/
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age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
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BUG_ON(age > 2);
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BUG_ON(age > 1);
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if (!age)
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rb_erase(&rmap_item->node, &root_unstable_tree);
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ksm_pages_unshared--;
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@ -546,37 +541,6 @@ static int unmerge_and_remove_all_rmap_items(void)
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return err;
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}
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static void remove_mm_from_lists(struct mm_struct *mm)
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{
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struct mm_slot *mm_slot;
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spin_lock(&ksm_mmlist_lock);
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mm_slot = get_mm_slot(mm);
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/*
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* This mm_slot is always at the scanning cursor when we're
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* called from scan_get_next_rmap_item; but it's a special
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* case when we're called from __ksm_exit.
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*/
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if (ksm_scan.mm_slot == mm_slot) {
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ksm_scan.mm_slot = list_entry(
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mm_slot->mm_list.next, struct mm_slot, mm_list);
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ksm_scan.address = 0;
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ksm_scan.rmap_item = list_entry(
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&ksm_scan.mm_slot->rmap_list, struct rmap_item, link);
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if (ksm_scan.mm_slot == &ksm_mm_head)
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ksm_scan.seqnr++;
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}
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hlist_del(&mm_slot->link);
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list_del(&mm_slot->mm_list);
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spin_unlock(&ksm_mmlist_lock);
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remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
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free_mm_slot(mm_slot);
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clear_bit(MMF_VM_MERGEABLE, &mm->flags);
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}
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static u32 calc_checksum(struct page *page)
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{
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u32 checksum;
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@ -1241,33 +1205,31 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
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}
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}
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if (!ksm_scan.address) {
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/*
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* We've completed a full scan of all vmas, holding mmap_sem
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* throughout, and found no VM_MERGEABLE: so do the same as
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* __ksm_exit does to remove this mm from all our lists now.
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*/
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remove_mm_from_lists(mm);
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up_read(&mm->mmap_sem);
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slot = ksm_scan.mm_slot;
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if (slot != &ksm_mm_head)
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goto next_mm;
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return NULL;
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}
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/*
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* Nuke all the rmap_items that are above this current rmap:
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* because there were no VM_MERGEABLE vmas with such addresses.
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*/
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remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
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up_read(&mm->mmap_sem);
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spin_lock(&ksm_mmlist_lock);
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slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
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ksm_scan.mm_slot = slot;
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ksm_scan.mm_slot = list_entry(slot->mm_list.next,
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struct mm_slot, mm_list);
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if (ksm_scan.address == 0) {
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/*
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* We've completed a full scan of all vmas, holding mmap_sem
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* throughout, and found no VM_MERGEABLE: so do the same as
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* __ksm_exit does to remove this mm from all our lists now.
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*/
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hlist_del(&slot->link);
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list_del(&slot->mm_list);
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free_mm_slot(slot);
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clear_bit(MMF_VM_MERGEABLE, &mm->flags);
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}
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spin_unlock(&ksm_mmlist_lock);
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up_read(&mm->mmap_sem);
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/* Repeat until we've completed scanning the whole list */
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slot = ksm_scan.mm_slot;
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if (slot != &ksm_mm_head)
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goto next_mm;
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@ -1408,13 +1370,38 @@ int __ksm_enter(struct mm_struct *mm)
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void __ksm_exit(struct mm_struct *mm)
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{
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struct mm_slot *mm_slot;
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/*
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* This process is exiting: doesn't hold and doesn't need mmap_sem;
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* but we do need to exclude ksmd and other exiters while we modify
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* the various lists and trees.
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*/
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mutex_lock(&ksm_thread_mutex);
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remove_mm_from_lists(mm);
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spin_lock(&ksm_mmlist_lock);
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mm_slot = get_mm_slot(mm);
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if (!list_empty(&mm_slot->rmap_list)) {
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spin_unlock(&ksm_mmlist_lock);
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remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
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spin_lock(&ksm_mmlist_lock);
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}
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if (ksm_scan.mm_slot == mm_slot) {
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ksm_scan.mm_slot = list_entry(
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mm_slot->mm_list.next, struct mm_slot, mm_list);
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ksm_scan.address = 0;
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ksm_scan.rmap_item = list_entry(
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&ksm_scan.mm_slot->rmap_list, struct rmap_item, link);
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if (ksm_scan.mm_slot == &ksm_mm_head)
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ksm_scan.seqnr++;
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}
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hlist_del(&mm_slot->link);
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list_del(&mm_slot->mm_list);
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spin_unlock(&ksm_mmlist_lock);
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free_mm_slot(mm_slot);
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clear_bit(MMF_VM_MERGEABLE, &mm->flags);
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mutex_unlock(&ksm_thread_mutex);
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}
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