[02/33] mm: Add an unlock function for PG_private_2/PG_fscache

Commit Message

David Howells Feb. 15, 2021, 3:44 p.m. UTC

Add a function, unlock_page_private_2(), to unlock PG_private_2 analogous
to that of PG_lock.  Add a kerneldoc banner to that indicating the example
usage case.

A wrapper will need to be placed in the netfs header in the patch that adds
that.

[This implements a suggestion by Linus to not mix the terminology of
 PG_private_2 and PG_fscache in the mm core function]

Suggested-by: Linus Torvalds <[e-mail]>
Signed-off-by: David Howells <[e-mail]>
cc: Linus Torvalds <[e-mail]>
cc: Matthew Wilcox (Oracle) <[e-mail]>
cc: Alexander Viro <[e-mail]>
cc: Christoph Hellwig <[e-mail]>
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
Link: https://lore.kernel.org/linux-fsdevel/[e-mail]/
Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wjgA-74ddehziVk=[e-mail]/
---

 include/linux/pagemap.h |    1 +
 mm/filemap.c            |   20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

Comments

Christoph Hellwig Feb. 16, 2021, 10:26 a.m. UTC | #1

> +extern void unlock_page_private_2(struct page *page);

No need for the extern.

Otherwise this looks good:

Reviewed-by: Christoph Hellwig <[e-mail]>

Patch

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index d5570deff400..365a28ece763 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -591,6 +591,7 @@  extern int __lock_page_async(struct page *page, struct wait_page_queue *wait);
 extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
 				unsigned int flags);
 extern void unlock_page(struct page *page);
+extern void unlock_page_private_2(struct page *page);
 
 /*
  * Return true if the page was successfully locked
diff --git a/mm/filemap.c b/mm/filemap.c
index 5c9d564317a5..7d321152d579 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1466,6 +1466,26 @@  void unlock_page(struct page *page)
 }
 EXPORT_SYMBOL(unlock_page);
 
+/**
+ * unlock_page_private_2 - Unlock a page that's locked with PG_private_2
+ * @page: The page
+ *
+ * Unlocks a page that's locked with PG_private_2 and wakes up sleepers in
+ * wait_on_page_private_2().
+ *
+ * This is, for example, used when a netfs page is being written to a local
+ * disk cache, thereby allowing writes to the cache for the same page to be
+ * serialised.
+ */
+void unlock_page_private_2(struct page *page)
+{
+	page = compound_head(page);
+	VM_BUG_ON_PAGE(!PagePrivate2(page), page);
+	clear_bit_unlock(PG_private_2, &page->flags);
+	wake_up_page_bit(page, PG_private_2);
+}
+EXPORT_SYMBOL(unlock_page_private_2);
+
 /**
  * end_page_writeback - end writeback against a page
  * @page: the page