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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>
This commit is contained in:
Hugh Dickins 2009-09-21 17:02:17 -07:00 committed by Linus Torvalds
parent d952b79136
commit cd551f9751
1 changed files with 42 additions and 55 deletions
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97
mm/ksm.c
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@ -444,14 +444,9 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
* But __ksm_exit has to be careful: do the rb_erase
* if it's interrupting a scan, and this rmap_item was
* inserted by this scan rather than left from before.
*
* Because of the case in which remove_mm_from_lists
* increments seqnr before removing rmaps, unstable_nr
* may even be 2 behind seqnr, but should never be
* further behind. Yes, I did have trouble with this!
*/
age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
BUG_ON(age > 2);
BUG_ON(age > 1);
if (!age)
rb_erase(&rmap_item->node, &root_unstable_tree);
ksm_pages_unshared--;
@ -546,37 +541,6 @@ out:
return err;
}
static void remove_mm_from_lists(struct mm_struct *mm)
{
struct mm_slot *mm_slot;
spin_lock(&ksm_mmlist_lock);
mm_slot = get_mm_slot(mm);
/*
* This mm_slot is always at the scanning cursor when we're
* called from scan_get_next_rmap_item; but it's a special
* case when we're called from __ksm_exit.
*/
if (ksm_scan.mm_slot == mm_slot) {
ksm_scan.mm_slot = list_entry(
mm_slot->mm_list.next, struct mm_slot, mm_list);
ksm_scan.address = 0;
ksm_scan.rmap_item = list_entry(
&ksm_scan.mm_slot->rmap_list, struct rmap_item, link);
if (ksm_scan.mm_slot == &ksm_mm_head)
ksm_scan.seqnr++;
}
hlist_del(&mm_slot->link);
list_del(&mm_slot->mm_list);
spin_unlock(&ksm_mmlist_lock);
remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
free_mm_slot(mm_slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
}
static u32 calc_checksum(struct page *page)
{
u32 checksum;
@ -1241,33 +1205,31 @@ next_mm:
}
}
if (!ksm_scan.address) {
/*
* We've completed a full scan of all vmas, holding mmap_sem
* throughout, and found no VM_MERGEABLE: so do the same as
* __ksm_exit does to remove this mm from all our lists now.
*/
remove_mm_from_lists(mm);
up_read(&mm->mmap_sem);
slot = ksm_scan.mm_slot;
if (slot != &ksm_mm_head)
goto next_mm;
return NULL;
}
/*
* Nuke all the rmap_items that are above this current rmap:
* because there were no VM_MERGEABLE vmas with such addresses.
*/
remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
up_read(&mm->mmap_sem);
spin_lock(&ksm_mmlist_lock);
slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
ksm_scan.mm_slot = slot;
ksm_scan.mm_slot = list_entry(slot->mm_list.next,
struct mm_slot, mm_list);
if (ksm_scan.address == 0) {
/*
* We've completed a full scan of all vmas, holding mmap_sem
* throughout, and found no VM_MERGEABLE: so do the same as
* __ksm_exit does to remove this mm from all our lists now.
*/
hlist_del(&slot->link);
list_del(&slot->mm_list);
free_mm_slot(slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
}
spin_unlock(&ksm_mmlist_lock);
up_read(&mm->mmap_sem);
/* Repeat until we've completed scanning the whole list */
slot = ksm_scan.mm_slot;
if (slot != &ksm_mm_head)
goto next_mm;
@ -1408,13 +1370,38 @@ int __ksm_enter(struct mm_struct *mm)
void __ksm_exit(struct mm_struct *mm)
{
struct mm_slot *mm_slot;
/*
* This process is exiting: doesn't hold and doesn't need mmap_sem;
* but we do need to exclude ksmd and other exiters while we modify
* the various lists and trees.
*/
mutex_lock(&ksm_thread_mutex);
remove_mm_from_lists(mm);
spin_lock(&ksm_mmlist_lock);
mm_slot = get_mm_slot(mm);
if (!list_empty(&mm_slot->rmap_list)) {
spin_unlock(&ksm_mmlist_lock);
remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
spin_lock(&ksm_mmlist_lock);
}
if (ksm_scan.mm_slot == mm_slot) {
ksm_scan.mm_slot = list_entry(
mm_slot->mm_list.next, struct mm_slot, mm_list);
ksm_scan.address = 0;
ksm_scan.rmap_item = list_entry(
&ksm_scan.mm_slot->rmap_list, struct rmap_item, link);
if (ksm_scan.mm_slot == &ksm_mm_head)
ksm_scan.seqnr++;
}
hlist_del(&mm_slot->link);
list_del(&mm_slot->mm_list);
spin_unlock(&ksm_mmlist_lock);
free_mm_slot(mm_slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
mutex_unlock(&ksm_thread_mutex);
}