From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
TTU_MIGRATION is used to convert pte into migration entry until thp split
completes. This behavior conflicts with thp migration added later patches,
so let's introduce a new TTU flag specifically for freezing.
try_to_unmap() is used both for thp split (via freeze_page()) and page
migration (via __unmap_and_move()). In freeze_page(), ttu_flag given for
head page is like below (assuming anonymous thp):
(TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED | \
TTU_MIGRATION | TTU_SPLIT_HUGE_PMD)
and ttu_flag given for tail pages is:
(TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED | \
TTU_MIGRATION)
__unmap_and_move() calls try_to_unmap() with ttu_flag:
(TTU_MIGRATION | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS)
Now I'm trying to insert a branch for thp migration at the top of
try_to_unmap_one() like below
static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
unsigned long address, void *arg)
{
...
if (flags & TTU_MIGRATION) {
if (!PageHuge(page) && PageTransCompound(page)) {
set_pmd_migration_entry(page, vma, address);
goto out;
}
}
, so try_to_unmap() for tail pages called by thp split can go into thp
migration code path (which converts *pmd* into migration entry), while
the expectation is to freeze thp (which converts *pte* into migration entry.)
I detected this failure as a "bad page state" error in a testcase where
split_huge_page() is called from queue_pages_pte_range().
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
---
include/linux/rmap.h | 3 ++-
mm/huge_memory.c | 2 +-
mm/rmap.c | 7 ++++---
3 files changed, 7 insertions(+), 5 deletions(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index fee10d744ebd..58803b6e7f82 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -93,8 +93,9 @@ enum ttu_flags {
TTU_BATCH_FLUSH = 0x40, /* Batch TLB flushes where possible
* and caller guarantees they will
* do a final flush if necessary */
- TTU_RMAP_LOCKED = 0x80 /* do not grab rmap lock:
+ TTU_RMAP_LOCKED = 0x80, /* do not grab rmap lock:
* caller holds it */
+ TTU_SPLIT_FREEZE = 0x100, /* freeze pte under splitting thp */
};
#ifdef CONFIG_MMU
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f42d4d0a3019..e32ccbd8ee3a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2142,7 +2142,7 @@ static void freeze_page(struct page *page)
VM_BUG_ON_PAGE(!PageHead(page), page);
if (PageAnon(page))
- ttu_flags |= TTU_MIGRATION;
+ ttu_flags |= TTU_SPLIT_FREEZE;
ret = try_to_unmap(page, ttu_flags);
VM_BUG_ON_PAGE(ret, page);
diff --git a/mm/rmap.c b/mm/rmap.c
index e4391100af51..555cc7ebacf6 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1304,7 +1304,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
if (flags & TTU_SPLIT_HUGE_PMD) {
split_huge_pmd_address(vma, address,
- flags & TTU_MIGRATION, page);
+ flags & TTU_SPLIT_FREEZE, page);
}
while (page_vma_mapped_walk(&pvmw)) {
@@ -1390,7 +1390,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
*/
dec_mm_counter(mm, mm_counter(page));
} else if (IS_ENABLED(CONFIG_MIGRATION) &&
- (flags & TTU_MIGRATION)) {
+ (flags & (TTU_MIGRATION|TTU_SPLIT_FREEZE))) {
swp_entry_t entry;
pte_t swp_pte;
/*
@@ -1521,7 +1521,8 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
* locking requirements of exec(), migration skips
* temporary VMAs until after exec() completes.
*/
- if ((flags & TTU_MIGRATION) && !PageKsm(page) && PageAnon(page))
+ if ((flags & (TTU_MIGRATION|TTU_SPLIT_FREEZE))
+ && !PageKsm(page) && PageAnon(page))
rwc.invalid_vma = invalid_migration_vma;
if (flags & TTU_RMAP_LOCKED)
--
2.11.0
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
