linux-kernel - [PATCH 01/10] include/linux/pagemap.h: introduce attach/detach_page

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Message-Id: <20200517214718.468-2-guoqing.jiang@cloud.ionos.com>
Date:   Sun, 17 May 2020 23:47:09 +0200
From:   Guoqing Jiang <guoqing.jiang@...ud.ionos.com>
To:     akpm@...ux-foundation.org, viro@...iv.linux.org.uk
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        david@...morbit.com, hch@...radead.org, willy@...radead.org,
        Guoqing Jiang <guoqing.jiang@...ud.ionos.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Yafang Shao <laoar.shao@...il.com>, Song Liu <song@...nel.org>,
        linux-raid@...r.kernel.org, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org,
        Anton Altaparmakov <anton@...era.com>,
        linux-ntfs-dev@...ts.sourceforge.net,
        Mike Marshall <hubcap@...ibond.com>,
        Martin Brandenburg <martin@...ibond.com>,
        devel@...ts.orangefs.org, Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Roman Gushchin <guro@...com>,
        Andreas Dilger <adilger@...ger.ca>
Subject: [PATCH 01/10] include/linux/pagemap.h: introduce attach/detach_page_private

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/detach_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 suggestions about
the function name from Alexander Viro, Andreas Grünbacher, Christoph
Hellwig and Matthew Wilcox.

Suggested-by: Matthew Wilcox <willy@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Darrick J. Wong" <darrick.wong@...cle.com>
Cc: William Kucharski <william.kucharski@...cle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Andreas Gruenbacher <agruenba@...hat.com>
Cc: Yang Shi <yang.shi@...ux.alibaba.com>
Cc: Yafang Shao <laoar.shao@...il.com>
Cc: Song Liu <song@...nel.org>
Cc: linux-raid@...r.kernel.org
Cc: Chris Mason <clm@...com>
Cc: Josef Bacik <josef@...icpanda.com>
Cc: David Sterba <dsterba@...e.com>
Cc: linux-btrfs@...r.kernel.org
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: Chao Yu <chao@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net
Cc: Christoph Hellwig <hch@...radead.org>
Cc: linux-xfs@...r.kernel.org
Cc: Anton Altaparmakov <anton@...era.com>
Cc: linux-ntfs-dev@...ts.sourceforge.net
Cc: Mike Marshall <hubcap@...ibond.com>
Cc: Martin Brandenburg <martin@...ibond.com>
Cc: devel@...ts.orangefs.org
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Roman Gushchin <guro@...com>
Cc: Andreas Dilger <adilger@...ger.ca>
Signed-off-by: Guoqing Jiang <guoqing.jiang@...ud.ionos.com>
---
No change since RFC V3.

RFC V2 -> RFC V3:
1. rename clear_page_private to detach_page_private.
2. updated the comments for the two functions.

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 | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c6348c50136f..8e085713150c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -208,6 +208,43 @@ static inline int page_cache_add_speculative(struct page *page, int count)
 	return __page_cache_add_speculative(page, count);
 }
 
+/**
+ * attach_page_private - Attach private data to a page.
+ * @page: Page to attach data to.
+ * @data: Data to attach to page.
+ *
+ * Attaching private data to a page increments the page's reference count.
+ * The data must be detached before the page will be freed.
+ */
+static inline void attach_page_private(struct page *page, void *data)
+{
+	get_page(page);
+	set_page_private(page, (unsigned long)data);
+	SetPagePrivate(page);
+}
+
+/**
+ * detach_page_private - Detach private data from a page.
+ * @page: Page to detach data from.
+ *
+ * Removes the data that was previously attached to the page and decrements
+ * the refcount on the page.
+ *
+ * Return: Data that was attached to the page.
+ */
+static inline void *detach_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;
+}
+
 #ifdef CONFIG_NUMA
 extern struct page *__page_cache_alloc(gfp_t gfp);
 #else
-- 
2.17.1