From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
By moving PG_writeback down into the low bits of the page flags, we can
use clear_bit_unlock_is_negative_byte() for writeback as well as the
lock bit. wake_up_page() then has no more callers. Given the other
code being executed between the clear and the test, this is not going
to be as dramatic a win as it was for PageLocked, but symmetry between
the two is nice and lets us remove some code.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
include/linux/page-flags.h | 6 +++---
mm/filemap.c | 19 ++++++-------------
mm/page-writeback.c | 37 ++++++++++++++++++++-----------------
3 files changed, 29 insertions(+), 33 deletions(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 222f6f7b2bb3..96c7d220c8cf 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 */
@@ -545,7 +545,7 @@ static __always_inline void SetPageUptodate(struct page *page)
CLEARPAGEFLAG(Uptodate, uptodate, PF_NO_TAIL)
-int test_clear_page_writeback(struct page *page);
+bool __clear_page_writeback(struct page *page);
int __test_set_page_writeback(struct page *page, bool keep_write);
#define test_set_page_writeback(page) \
diff --git a/mm/filemap.c b/mm/filemap.c
index 312afbfcb49a..bfe1782a7b98 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1084,13 +1084,6 @@ static void wake_up_page_bit(struct page *page, int bit_nr)
spin_unlock_irqrestore(&q->lock, flags);
}
-static void wake_up_page(struct page *page, int bit)
-{
- if (!PageWaiters(page))
- return;
- wake_up_page_bit(page, bit);
-}
-
/*
* A choice of three behaviors for wait_on_page_bit_common():
*/
@@ -1266,6 +1259,7 @@ 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))
@@ -1279,23 +1273,22 @@ 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);
rotate_reclaimable_page(page);
}
- if (!test_clear_page_writeback(page))
- BUG();
-
- smp_mb__after_atomic();
- wake_up_page(page, PG_writeback);
+ VM_BUG_ON_PAGE(!PageWriteback(page), page);
+ if (__clear_page_writeback(page))
+ wake_up_page_bit(page, PG_writeback);
}
EXPORT_SYMBOL(end_page_writeback);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b7f3d0766a5f..4d675a7b81e6 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -595,7 +595,7 @@ static void wb_domain_writeout_inc(struct wb_domain *dom,
/*
* Increment @wb's writeout completion count and the global writeout
- * completion count. Called from test_clear_page_writeback().
+ * completion count. Called from __clear_page_writeback().
*/
static inline void __wb_writeout_inc(struct bdi_writeback *wb)
{
@@ -2711,12 +2711,19 @@ int clear_page_dirty_for_io(struct page *page)
}
EXPORT_SYMBOL(clear_page_dirty_for_io);
-int test_clear_page_writeback(struct page *page)
+#define clear_writeback_bit(page) \
+ clear_bit_unlock_is_negative_byte(PG_writeback, &page->flags)
+
+/*
+ * The return value is whether there are waiters pending, not whether
+ * the flag was set.
+ */
+bool __clear_page_writeback(struct page *page)
{
struct address_space *mapping = page_mapping(page);
struct mem_cgroup *memcg;
struct lruvec *lruvec;
- int ret;
+ bool ret;
memcg = lock_page_memcg(page);
lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
@@ -2726,16 +2733,14 @@ int test_clear_page_writeback(struct page *page)
unsigned long flags;
xa_lock_irqsave(&mapping->i_pages, flags);
- ret = TestClearPageWriteback(page);
- if (ret) {
- __xa_clear_mark(&mapping->i_pages, page_index(page),
+ ret = clear_writeback_bit(page);
+ __xa_clear_mark(&mapping->i_pages, page_index(page),
PAGECACHE_TAG_WRITEBACK);
- if (bdi_cap_account_writeback(bdi)) {
- struct bdi_writeback *wb = inode_to_wb(inode);
+ if (bdi_cap_account_writeback(bdi)) {
+ struct bdi_writeback *wb = inode_to_wb(inode);
- dec_wb_stat(wb, WB_WRITEBACK);
- __wb_writeout_inc(wb);
- }
+ dec_wb_stat(wb, WB_WRITEBACK);
+ __wb_writeout_inc(wb);
}
if (mapping->host && !mapping_tagged(mapping,
@@ -2744,7 +2749,7 @@ int test_clear_page_writeback(struct page *page)
xa_unlock_irqrestore(&mapping->i_pages, flags);
} else {
- ret = TestClearPageWriteback(page);
+ ret = clear_writeback_bit(page);
}
/*
* NOTE: Page might be free now! Writeback doesn't hold a page
@@ -2752,11 +2757,9 @@ int test_clear_page_writeback(struct page *page)
* the clearing of PG_writeback. The below can only access
* page state that is static across allocation cycles.
*/
- if (ret) {
- dec_lruvec_state(lruvec, NR_WRITEBACK);
- dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
- inc_node_page_state(page, NR_WRITTEN);
- }
+ dec_lruvec_state(lruvec, NR_WRITEBACK);
+ dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
+ inc_node_page_state(page, NR_WRITTEN);
__unlock_page_memcg(memcg);
return ret;
}
--
2.25.1
