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

David Howells
2021-02-15T15:44:53Z

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 <torvalds@linux-foundation.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Matthew Wilcox (Oracle) <willy@infradead.org>
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Christoph Hellwig <hch@lst.de>
cc: linux-mm@kvack.org
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/linux-fsdevel/1330473.1612974547@warthog.procyon.org.uk/
Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wjgA-74ddehziVk=XAEMTKswPu1Yw4uaro1R3ibs27ztw@mail.gmail.com/
---

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

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