On 5/1/20 12:10 AM, Andreas Grünbacher wrote:

Hi,

Am Do., 30. Apr. 2020 um 23:56 Uhr schrieb Guoqing Jiang
[off-list ref]:

quoted

The logic in attach_page_buffers and  __clear_page_buffers are quite
paired, but

1. they are located in different files.

2. attach_page_buffers is implemented in buffer_head.h, so it could be
    used by other files. But __clear_page_buffers is static function in
    buffer.c and other potential users can't call the function, md-bitmap
    even copied the function.

So, introduce the new attach/clear_page_private to replace them. With
the new pair of function, we will remove the usage of attach_page_buffers
and  __clear_page_buffers in next patches. Thanks for the new names from
Christoph Hellwig.

Suggested-by: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "Darrick J. Wong" <redacted>
Cc: William Kucharski <redacted>
Cc: "Kirill A. Shutemov" <redacted>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Yang Shi <redacted>
Cc: Yafang Shao <redacted>
Cc: Song Liu <song@kernel.org>
Cc: linux-raid@vger.kernel.org
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Chao Yu <chao@kernel.org>
Cc: linux-f2fs-devel@lists.sourceforge.net
Cc: Christoph Hellwig <hch@infradead.org>
Cc: linux-xfs@vger.kernel.org
Cc: Anton Altaparmakov <redacted>
Cc: linux-ntfs-dev@lists.sourceforge.net
Cc: Mike Marshall <hubcap@omnibond.com>
Cc: Martin Brandenburg <martin@omnibond.com>
Cc: devel@lists.orangefs.org
Cc: Thomas Gleixner <redacted>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Roman Gushchin <redacted>
Cc: Andreas Dilger <redacted>
Signed-off-by: Guoqing Jiang <redacted>
---
RFC -> RFC V2:  Address the comments from Christoph Hellwig
1. change function names to attach/clear_page_private and add comments.
2. change the return type of attach_page_private.

  include/linux/pagemap.h | 35 +++++++++++++++++++++++++++++++++++
  1 file changed, 35 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a8f7bd8ea1c6..2e515f210b18 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h

@@ -205,6 +205,41 @@ static inline int page_cache_add_speculative(struct page *page, int count)
         return __page_cache_add_speculative(page, count);
  }

+/**
+ * attach_page_private - attach data to page's private field and set PG_private.
+ * @page: page to be attached and set flag.
+ * @data: data to attach to page's private field.
+ *
+ * Need to take reference as mm.h said "Setting PG_private should also increment
+ * the refcount".
+ */
+static inline void attach_page_private(struct page *page, void *data)
+{
+       get_page(page);
+       set_page_private(page, (unsigned long)data);
+       SetPagePrivate(page);
+}
+
+/**
+ * clear_page_private - clear page's private field and PG_private.
+ * @page: page to be cleared.
+ *
+ * The counterpart function of attach_page_private.
+ * Return: private data of page or NULL if page doesn't have private data.
+ */
+static inline void *clear_page_private(struct page *page)
+{
+       void *data = (void *)page_private(page);
+
+       if (!PagePrivate(page))
+               return NULL;
+       ClearPagePrivate(page);
+       set_page_private(page, 0);
+       put_page(page);
+
+       return data;
+}
+

I like this in general, but the name clear_page_private suggests that
this might be the inverse operation of set_page_private, which it is
not. So maybe this can be renamed to detach_page_private to more
clearly indicate that it pairs with attach_page_private?

Yes, the new name is better, thank you!

Cheers,
Guoqing