[PATCH 17/17] mm: Use folio_xor_flags_has_waiters() in folio_end_writeback()

Matthew Wilcox (Oracle)
2023-09-15T18:38:45Z

Match how folio_unlock() works by combining the test for PG_waiters with
the clearing of PG_writeback. This should have a small performance win,
and removes the last user of folio_wake().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
mm/filemap.c | 15 +++------------
mm/internal.h | 2 +-
mm/page-writeback.c | 9 ++++++---
3 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 53c0d71aae8e..f57b62d65001 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1177,13 +1177,6 @@ static void folio_wake_bit(struct folio *folio, int bit_nr)
spin_unlock_irqrestore(&q->lock, flags);
}

-static void folio_wake(struct folio *folio, int bit)
-{
- if (!folio_test_waiters(folio))
- return;
- folio_wake_bit(folio, bit);
-}
-
/*
* A choice of three behaviors for folio_wait_bit_common():
*/
@@ -1620,13 +1613,11 @@ void folio_end_writeback(struct folio *folio)
* Writeback does not hold a folio reference of its own, relying
* on truncation to wait for the clearing of PG_writeback.
* But here we must make sure that the folio is not freed and
- * reused before the folio_wake().
+ * reused before the folio_wake_bit().
*/
folio_get(folio);
- __folio_end_writeback(folio);
-
- smp_mb__after_atomic();
- folio_wake(folio, PG_writeback);
+ if (__folio_end_writeback(folio))
+ folio_wake_bit(folio, PG_writeback);
acct_reclaim_writeback(folio);
folio_put(folio);
}
diff --git a/mm/internal.h b/mm/internal.h
index ccb08dd9b5ec..30cf724ddbce 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -105,7 +105,7 @@ static inline void wake_throttle_isolated(pg_data_t *pgdat)

vm_fault_t do_swap_page(struct vm_fault *vmf);
void folio_rotate_reclaimable(struct folio *folio);
-void __folio_end_writeback(struct folio *folio);
+bool __folio_end_writeback(struct folio *folio);
void deactivate_file_folio(struct folio *folio);
void folio_activate(struct folio *folio);

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 410b53e888e3..c52514fe1d23 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2940,10 +2940,11 @@ static void wb_inode_writeback_end(struct bdi_writeback *wb)
spin_unlock_irqrestore(&wb->work_lock, flags);
}

-void __folio_end_writeback(struct folio *folio)
+bool __folio_end_writeback(struct folio *folio)
{
long nr = folio_nr_pages(folio);
struct address_space *mapping = folio_mapping(folio);
+ bool ret;

folio_memcg_lock(folio);
if (mapping && mapping_use_writeback_tags(mapping)) {
@@ -2952,7 +2953,7 @@ void __folio_end_writeback(struct folio *folio)
unsigned long flags;

xa_lock_irqsave(&mapping->i_pages, flags);
- folio_test_clear_writeback(folio);
+ ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
__xa_clear_mark(&mapping->i_pages, folio_index(folio),
PAGECACHE_TAG_WRITEBACK);
if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
@@ -2970,13 +2971,15 @@ void __folio_end_writeback(struct folio *folio)

xa_unlock_irqrestore(&mapping->i_pages, flags);
} else {
- folio_test_clear_writeback(folio);
+ ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
}

lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
node_stat_mod_folio(folio, NR_WRITTEN, nr);
folio_memcg_unlock(folio);
+
+ return ret;
}

bool __folio_start_writeback(struct folio *folio, bool keep_write)
--
2.40.1