[PATCH 2/2] sched, numa, mm: Fixes and cleanups indo_huge_pmd_numa_page()
From: Hugh Dickins
Date: Tue Nov 13 2012 - 21:29:33 EST
Refuse to migrate a THPage if its page count is raised: that covers both
the case when it is mapped into another address space, and the case
when it has been pinned by get_user_pages(), fast or slow.
Repeat this check each time we recheck pmd_same() under page_table_lock:
it is unclear how necessary this is, perhaps once after lock_page() or
once after isolate_lru_page() would be enough; but normal page migration
certainly checks page count, and we often think "ah, this is safe against
page migration because its page count is raised" - though sadly without
thinking through what serialization supports that.
Do not proceed with migration when PageLRU is unset: such a page may
well be in a private list or on a pagevec, about to be added to LRU at
any instant: checking PageLRU under zone lock, as isolate_lru_page() does,
is essential before proceeding safely.
Replace trylock_page and BUG by __set_page_locked: here the page has
been allocated a few lines earlier. And SetPageSwapBacked: it is set
later, but there may be an error path which needs it set earlier.
On error path reverse the Active, Unevictable, Mlocked changes made
by migrate_page_copy(). Update mlock_migrate_page() to account for
THPages correctly now that it can get called on them.
Cleanup: rearrange unwinding slightly, removing a few blank lines.
Previous-Version-Tested-by: Zhouping Liu <zliu@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
I did not understand at all how pmd_page(entry) might be NULL, but
assumed that check is there for good reason and did not remove it.
mm/huge_memory.c | 60 +++++++++++++++++++++++----------------------
mm/internal.h | 5 ++-
2 files changed, 34 insertions(+), 31 deletions(-)
--- mmotm/mm/huge_memory.c 2012-11-13 14:51:04.000321370 -0800
+++ linux/mm/huge_memory.c 2012-11-13 15:01:01.892335579 -0800
@@ -751,9 +751,9 @@ void do_huge_pmd_numa_page(struct mm_str
{
unsigned long haddr = address & HPAGE_PMD_MASK;
struct mem_cgroup *memcg = NULL;
- struct page *new_page = NULL;
+ struct page *new_page;
struct page *page = NULL;
- int node, lru;
+ int node = -1;
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(*pmd, entry)))
@@ -770,7 +770,17 @@ void do_huge_pmd_numa_page(struct mm_str
VM_BUG_ON(!PageCompound(page) || !PageHead(page));
get_page(page);
- node = mpol_misplaced(page, vma, haddr);
+ /*
+ * Do not migrate this page if it is mapped anywhere else.
+ * Do not migrate this page if its count has been raised.
+ * Our caller's down_read of mmap_sem excludes fork raising
+ * mapcount; but recheck page count below whenever we take
+ * page_table_lock - although it's unclear what pin we are
+ * protecting against, since get_user_pages() or GUP fast
+ * would have to fault it present before they could proceed.
+ */
+ if (page_count(page) == 2)
+ node = mpol_misplaced(page, vma, haddr);
if (node != -1)
goto migrate;
}
@@ -794,7 +804,7 @@ migrate:
lock_page(page);
spin_lock(&mm->page_table_lock);
- if (unlikely(!pmd_same(*pmd, entry))) {
+ if (unlikely(!pmd_same(*pmd, entry) || page_count(page) != 2)) {
spin_unlock(&mm->page_table_lock);
unlock_page(page);
put_page(page);
@@ -803,19 +813,17 @@ migrate:
spin_unlock(&mm->page_table_lock);
new_page = alloc_pages_node(node,
- (GFP_TRANSHUGE | GFP_THISNODE) & ~__GFP_WAIT,
- HPAGE_PMD_ORDER);
-
+ (GFP_TRANSHUGE | GFP_THISNODE) & ~__GFP_WAIT, HPAGE_PMD_ORDER);
if (!new_page)
goto alloc_fail;
- lru = PageLRU(page);
-
- if (lru && isolate_lru_page(page)) /* does an implicit get_page() */
+ if (isolate_lru_page(page)) { /* Does an implicit get_page() */
+ put_page(new_page);
goto alloc_fail;
+ }
- if (!trylock_page(new_page))
- BUG();
+ __set_page_locked(new_page);
+ SetPageSwapBacked(new_page);
/* anon mapping, we can simply copy page->mapping to the new page: */
new_page->mapping = page->mapping;
@@ -826,19 +834,22 @@ migrate:
WARN_ON(PageLRU(new_page));
spin_lock(&mm->page_table_lock);
- if (unlikely(!pmd_same(*pmd, entry))) {
+ if (unlikely(!pmd_same(*pmd, entry) || page_count(page) != 3)) {
spin_unlock(&mm->page_table_lock);
- if (lru)
- putback_lru_page(page);
+
+ /* Reverse changes made by migrate_page_copy() */
+ if (TestClearPageActive(new_page))
+ SetPageActive(page);
+ if (TestClearPageUnevictable(new_page))
+ SetPageUnevictable(page);
+ mlock_migrate_page(page, new_page);
unlock_page(new_page);
- ClearPageActive(new_page); /* Set by migrate_page_copy() */
- new_page->mapping = NULL;
put_page(new_page); /* Free it */
unlock_page(page);
+ putback_lru_page(page);
put_page(page); /* Drop the local reference */
-
return;
}
/*
@@ -867,26 +878,17 @@ migrate:
mem_cgroup_end_migration(memcg, page, new_page, true);
spin_unlock(&mm->page_table_lock);
- put_page(page); /* Drop the rmap reference */
-
task_numa_fault(node, HPAGE_PMD_NR);
- if (lru)
- put_page(page); /* drop the LRU isolation reference */
-
unlock_page(new_page);
-
unlock_page(page);
+ put_page(page); /* Drop the rmap reference */
+ put_page(page); /* Drop the LRU isolation reference */
put_page(page); /* Drop the local reference */
-
return;
alloc_fail:
- if (new_page)
- put_page(new_page);
-
unlock_page(page);
-
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(*pmd, entry))) {
put_page(page);
--- mmotm/mm/internal.h 2012-11-09 09:43:46.896046342 -0800
+++ linux/mm/internal.h 2012-11-13 15:01:01.892335579 -0800
@@ -218,11 +218,12 @@ static inline void mlock_migrate_page(st
{
if (TestClearPageMlocked(page)) {
unsigned long flags;
+ int nr_pages = hpage_nr_pages(page);
local_irq_save(flags);
- __dec_zone_page_state(page, NR_MLOCK);
+ __mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
SetPageMlocked(newpage);
- __inc_zone_page_state(newpage, NR_MLOCK);
+ __mod_zone_page_state(page_zone(newpage), NR_MLOCK, nr_pages);
local_irq_restore(flags);
}
}
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