Trying to set or clear PG_lru on tail pages has been considered buggy.
Enforce this rule by changing the policy for PG_lru from PF_HEAD to
PF_NO_TAIL. This means setting or clearing PG_lru on tail pages won't
be "corrected" by compound_page(). Such "correction" isn't helpful --
even if a piece of buggy code has gotten away with
compound_page(tail)->flags, it will run into trouble with lru list
addition and deletion because they use tail->lru rather than
compound_page(tail)->lru.
bloat-o-meter result:
add/remove: 0/0 grow/shrink: 0/11 up/down: 0/-535 (-535)
Signed-off-by: Yu Zhao <yuz...@google.com>
---
include/linux/page-flags.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 1995208a3763..c9626e54df8d 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -333,8 +333,8 @@ PAGEFLAG(Referenced, referenced, PF_HEAD)
__SETPAGEFLAG(Referenced, referenced, PF_HEAD)
PAGEFLAG(Dirty, dirty, PF_HEAD) TESTSCFLAG(Dirty, dirty, PF_HEAD)
__CLEARPAGEFLAG(Dirty, dirty, PF_HEAD)
-PAGEFLAG(LRU, lru, PF_HEAD) __CLEARPAGEFLAG(LRU, lru, PF_HEAD)
- TESTCLEARFLAG(LRU, lru, PF_HEAD)
+PAGEFLAG(LRU, lru, PF_NO_TAIL) __CLEARPAGEFLAG(LRU, lru, PF_NO_TAIL)
+ TESTCLEARFLAG(LRU, lru, PF_NO_TAIL)
PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)
TESTCLEARFLAG(Active, active, PF_HEAD)
PAGEFLAG(Workingset, workingset, PF_HEAD)
--
2.30.1.766.gb4fecdf3b7-goog
