[PATCH v14 027/138] mm/filemap: Add folio_wait_bit()

From: Matthew Wilcox (Oracle)
Date: Thu Jul 15 2021 - 00:00:19 EST

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Rename wait_on_page_bit() to folio_wait_bit(). We must always wait on
the folio, otherwise we won't be woken up due to the tail page hashing
to a different bucket from the head page.

This commit shrinks the kernel by 770 bytes, mostly due to moving
the page waitqueue lookup into folio_wait_bit_common().

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Reviewed-by: David Howells <dhowells@xxxxxxxxxx>
---
include/linux/pagemap.h | 10 +++---
mm/filemap.c | 77 +++++++++++++++++++----------------------
mm/page-writeback.c | 4 +--
3 files changed, 43 insertions(+), 48 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 96b62a2331fb..7eb02baf6f9f 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -729,11 +729,11 @@ static inline bool lock_page_or_retry(struct page *page, struct mm_struct *mm,
}

/*
- * This is exported only for wait_on_page_locked/wait_on_page_writeback, etc.,
+ * This is exported only for folio_wait_locked/folio_wait_writeback, etc.,
* and should not be used directly.
*/
-extern void wait_on_page_bit(struct page *page, int bit_nr);
-extern int wait_on_page_bit_killable(struct page *page, int bit_nr);
+void folio_wait_bit(struct folio *folio, int bit_nr);
+int folio_wait_bit_killable(struct folio *folio, int bit_nr);

/*
* Wait for a folio to be unlocked.
@@ -745,14 +745,14 @@ extern int wait_on_page_bit_killable(struct page *page, int bit_nr);
static inline void folio_wait_locked(struct folio *folio)
{
if (folio_test_locked(folio))
- wait_on_page_bit(&folio->page, PG_locked);
+ folio_wait_bit(folio, PG_locked);
}

static inline int folio_wait_locked_killable(struct folio *folio)
{
if (!folio_test_locked(folio))
return 0;
- return wait_on_page_bit_killable(&folio->page, PG_locked);
+ return folio_wait_bit_killable(folio, PG_locked);
}

static inline void wait_on_page_locked(struct page *page)
diff --git a/mm/filemap.c b/mm/filemap.c
index b5a0d546e436..b55c89d7997f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1102,7 +1102,7 @@ static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync,
*
* So update the flags atomically, and wake up the waiter
* afterwards to avoid any races. This store-release pairs
- * with the load-acquire in wait_on_page_bit_common().
+ * with the load-acquire in folio_wait_bit_common().
*/
smp_store_release(&wait->flags, flags | WQ_FLAG_WOKEN);
wake_up_state(wait->private, mode);
@@ -1183,7 +1183,7 @@ static void folio_wake(struct folio *folio, int bit)
}

/*
- * A choice of three behaviors for wait_on_page_bit_common():
+ * A choice of three behaviors for folio_wait_bit_common():
*/
enum behavior {
EXCLUSIVE, /* Hold ref to page and take the bit when woken, like
@@ -1198,16 +1198,16 @@ enum behavior {
};

/*
- * Attempt to check (or get) the page bit, and mark us done
+ * Attempt to check (or get) the folio flag, and mark us done
* if successful.
*/
-static inline bool trylock_page_bit_common(struct page *page, int bit_nr,
+static inline bool folio_trylock_flag(struct folio *folio, int bit_nr,
struct wait_queue_entry *wait)
{
if (wait->flags & WQ_FLAG_EXCLUSIVE) {
- if (test_and_set_bit(bit_nr, &page->flags))
+ if (test_and_set_bit(bit_nr, &folio->flags))
return false;
- } else if (test_bit(bit_nr, &page->flags))
+ } else if (test_bit(bit_nr, &folio->flags))
return false;

wait->flags |= WQ_FLAG_WOKEN | WQ_FLAG_DONE;
@@ -1217,9 +1217,10 @@ static inline bool trylock_page_bit_common(struct page *page, int bit_nr,
/* How many times do we accept lock stealing from under a waiter? */
int sysctl_page_lock_unfairness = 5;

-static inline int wait_on_page_bit_common(wait_queue_head_t *q,
- struct page *page, int bit_nr, int state, enum behavior behavior)
+static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
+ int state, enum behavior behavior)
{
+ wait_queue_head_t *q = page_waitqueue(&folio->page);
int unfairness = sysctl_page_lock_unfairness;
struct wait_page_queue wait_page;
wait_queue_entry_t *wait = &wait_page.wait;
@@ -1228,8 +1229,8 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
unsigned long pflags;

if (bit_nr == PG_locked &&
- !PageUptodate(page) && PageWorkingset(page)) {
- if (!PageSwapBacked(page)) {
+ !folio_test_uptodate(folio) && folio_test_workingset(folio)) {
+ if (!folio_test_swapbacked(folio)) {
delayacct_thrashing_start();
delayacct = true;
}
@@ -1239,7 +1240,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,

init_wait(wait);
wait->func = wake_page_function;
- wait_page.page = page;
+ wait_page.page = &folio->page;
wait_page.bit_nr = bit_nr;

repeat:
@@ -1254,7 +1255,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
* Do one last check whether we can get the
* page bit synchronously.
*
- * Do the SetPageWaiters() marking before that
+ * Do the folio_set_waiters() marking before that
* to let any waker we _just_ missed know they
* need to wake us up (otherwise they'll never
* even go to the slow case that looks at the
@@ -1265,8 +1266,8 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
* lock to avoid races.
*/
spin_lock_irq(&q->lock);
- SetPageWaiters(page);
- if (!trylock_page_bit_common(page, bit_nr, wait))
+ folio_set_waiters(folio);
+ if (!folio_trylock_flag(folio, bit_nr, wait))
__add_wait_queue_entry_tail(q, wait);
spin_unlock_irq(&q->lock);

@@ -1276,10 +1277,10 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
* see whether the page bit testing has already
* been done by the wake function.
*
- * We can drop our reference to the page.
+ * We can drop our reference to the folio.
*/
if (behavior == DROP)
- put_page(page);
+ folio_put(folio);

/*
* Note that until the "finish_wait()", or until
@@ -1316,7 +1317,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
*
* And if that fails, we'll have to retry this all.
*/
- if (unlikely(test_and_set_bit(bit_nr, &page->flags)))
+ if (unlikely(test_and_set_bit(bit_nr, folio_flags(folio, 0))))
goto repeat;

wait->flags |= WQ_FLAG_DONE;
@@ -1325,7 +1326,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,

/*
* If a signal happened, this 'finish_wait()' may remove the last
- * waiter from the wait-queues, but the PageWaiters bit will remain
+ * waiter from the wait-queues, but the folio waiters bit will remain
* set. That's ok. The next wakeup will take care of it, and trying
* to do it here would be difficult and prone to races.
*/
@@ -1356,19 +1357,17 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
return wait->flags & WQ_FLAG_WOKEN ? 0 : -EINTR;
}

-void wait_on_page_bit(struct page *page, int bit_nr)
+void folio_wait_bit(struct folio *folio, int bit_nr)
{
- wait_queue_head_t *q = page_waitqueue(page);
- wait_on_page_bit_common(q, page, bit_nr, TASK_UNINTERRUPTIBLE, SHARED);
+ folio_wait_bit_common(folio, bit_nr, TASK_UNINTERRUPTIBLE, SHARED);
}
-EXPORT_SYMBOL(wait_on_page_bit);
+EXPORT_SYMBOL(folio_wait_bit);

-int wait_on_page_bit_killable(struct page *page, int bit_nr)
+int folio_wait_bit_killable(struct folio *folio, int bit_nr)
{
- wait_queue_head_t *q = page_waitqueue(page);
- return wait_on_page_bit_common(q, page, bit_nr, TASK_KILLABLE, SHARED);
+ return folio_wait_bit_common(folio, bit_nr, TASK_KILLABLE, SHARED);
}
-EXPORT_SYMBOL(wait_on_page_bit_killable);
+EXPORT_SYMBOL(folio_wait_bit_killable);

/**
* put_and_wait_on_page_locked - Drop a reference and wait for it to be unlocked
@@ -1385,11 +1384,8 @@ EXPORT_SYMBOL(wait_on_page_bit_killable);
*/
int put_and_wait_on_page_locked(struct page *page, int state)
{
- wait_queue_head_t *q;
-
- page = compound_head(page);
- q = page_waitqueue(page);
- return wait_on_page_bit_common(q, page, PG_locked, state, DROP);
+ return folio_wait_bit_common(page_folio(page), PG_locked, state,
+ DROP);
}

/**
@@ -1483,9 +1479,10 @@ EXPORT_SYMBOL(end_page_private_2);
*/
void wait_on_page_private_2(struct page *page)
{
- page = compound_head(page);
- while (PagePrivate2(page))
- wait_on_page_bit(page, PG_private_2);
+ struct folio *folio = page_folio(page);
+
+ while (folio_test_private_2(folio))
+ folio_wait_bit(folio, PG_private_2);
}
EXPORT_SYMBOL(wait_on_page_private_2);

@@ -1502,11 +1499,11 @@ EXPORT_SYMBOL(wait_on_page_private_2);
*/
int wait_on_page_private_2_killable(struct page *page)
{
+ struct folio *folio = page_folio(page);
int ret = 0;

- page = compound_head(page);
- while (PagePrivate2(page)) {
- ret = wait_on_page_bit_killable(page, PG_private_2);
+ while (folio_test_private_2(folio)) {
+ ret = folio_wait_bit_killable(folio, PG_private_2);
if (ret < 0)
break;
}
@@ -1583,16 +1580,14 @@ EXPORT_SYMBOL_GPL(page_endio);
*/
void __folio_lock(struct folio *folio)
{
- wait_queue_head_t *q = page_waitqueue(&folio->page);
- wait_on_page_bit_common(q, &folio->page, PG_locked, TASK_UNINTERRUPTIBLE,
+ folio_wait_bit_common(folio, PG_locked, TASK_UNINTERRUPTIBLE,
EXCLUSIVE);
}
EXPORT_SYMBOL(__folio_lock);

int __folio_lock_killable(struct folio *folio)
{
- wait_queue_head_t *q = page_waitqueue(&folio->page);
- return wait_on_page_bit_common(q, &folio->page, PG_locked, TASK_KILLABLE,
+ return folio_wait_bit_common(folio, PG_locked, TASK_KILLABLE,
EXCLUSIVE);
}
EXPORT_SYMBOL_GPL(__folio_lock_killable);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index a078e9786cc4..b34278d05395 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2846,7 +2846,7 @@ void folio_wait_writeback(struct folio *folio)
{
while (folio_test_writeback(folio)) {
trace_wait_on_page_writeback(&folio->page, folio_mapping(folio));
- wait_on_page_bit(&folio->page, PG_writeback);
+ folio_wait_bit(folio, PG_writeback);
}
}
EXPORT_SYMBOL_GPL(folio_wait_writeback);
@@ -2868,7 +2868,7 @@ int folio_wait_writeback_killable(struct folio *folio)
{
while (folio_test_writeback(folio)) {
trace_wait_on_page_writeback(&folio->page, folio_mapping(folio));
- if (wait_on_page_bit_killable(&folio->page, PG_writeback))
+ if (folio_wait_bit_killable(folio, PG_writeback))
return -EINTR;
}

--
2.30.2

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Previous message: Matthew Wilcox (Oracle): "[PATCH v14 026/138] mm/writeback: Add folio_wait_stable()"
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