From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
By placing PG_writeback in the bottom byte along with PG_locked and
PG_waiters, we will be able to use the same optimisation as PG_locked
in a subsequent patch. Add BUILD_BUGs to ensure that all three bits
stay in the bottom byte.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
---
include/linux/page-flags.h | 4 ++--
mm/filemap.c | 4 +++-
2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 222f6f7b2bb3..af7c0ff5f517 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -103,13 +103,14 @@
*/
enum pageflags {
PG_locked, /* Page is locked. Don't touch. */
+ PG_writeback, /* Page is under writeback */
PG_referenced,
PG_uptodate,
PG_dirty,
PG_lru,
PG_active,
+ PG_waiters, /* Page has waiters, check its waitqueue */
PG_workingset,
- PG_waiters, /* Page has waiters, check its waitqueue. Must be bit #7 and in the same byte as "PG_locked" */
PG_error,
PG_slab,
PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/
@@ -117,7 +118,6 @@ enum pageflags {
PG_reserved,
PG_private, /* If pagecache, has fs-private data */
PG_private_2, /* If pagecache, has fs aux data */
- PG_writeback, /* Page is under writeback */
PG_head, /* A head page */
PG_mappedtodisk, /* Has blocks allocated on-disk */
PG_reclaim, /* To be reclaimed asap */
diff --git a/mm/filemap.c b/mm/filemap.c
index e475117e89eb..b7c5d2402370 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1266,6 +1266,7 @@ EXPORT_SYMBOL_GPL(add_page_wait_queue);
void unlock_page(struct page *page)
{
BUILD_BUG_ON(PG_waiters != 7);
+ BUILD_BUG_ON(PG_locked > 7);
page = compound_head(page);
VM_BUG_ON_PAGE(!PageLocked(page), page);
if (clear_bit_unlock_is_negative_byte(PG_locked, &page->flags))
@@ -1279,12 +1280,13 @@ EXPORT_SYMBOL(unlock_page);
*/
void end_page_writeback(struct page *page)
{
+ BUILD_BUG_ON(PG_writeback > 7);
/*
* TestClearPageReclaim could be used here but it is an atomic
* operation and overkill in this particular case. Failing to
* shuffle a page marked for immediate reclaim is too mild to
* justify taking an atomic operation penalty at the end of
- * ever page writeback.
+ * every page writeback.
*/
if (PageReclaim(page)) {
ClearPageReclaim(page);
--
2.25.1
