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From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Jonathan Corbet <corbet@lwn.net>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	linux-doc@vger.kernel.org,
	linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH 3/5] buffer: Add kernel-doc for try_to_free_buffers()
Date: Thu,  4 Jan 2024 16:36:50 +0000
Message-Id: <20240104163652.3705753-4-willy@infradead.org>
In-Reply-To: <20240104163652.3705753-1-willy@infradead.org>
References: <20240104163652.3705753-1-willy@infradead.org>
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The documentation for this function has become separated from it over
time; move it to the right place and turn it into kernel-doc.  Mild
editing of the content to make it more about what the function does, and
less about how it does it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/buffer.c | 44 ++++++++++++++++++++++++--------------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 31e171382e00..a657920802ac 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2863,26 +2863,6 @@ int sync_dirty_buffer(struct buffer_head *bh)
 }
 EXPORT_SYMBOL(sync_dirty_buffer);
 
-/*
- * try_to_free_buffers() checks if all the buffers on this particular folio
- * are unused, and releases them if so.
- *
- * Exclusion against try_to_free_buffers may be obtained by either
- * locking the folio or by holding its mapping's private_lock.
- *
- * If the folio is dirty but all the buffers are clean then we need to
- * be sure to mark the folio clean as well.  This is because the folio
- * may be against a block device, and a later reattachment of buffers
- * to a dirty folio will set *all* buffers dirty.  Which would corrupt
- * filesystem data on the same device.
- *
- * The same applies to regular filesystem folios: if all the buffers are
- * clean then we set the folio clean and proceed.  To do that, we require
- * total exclusion from block_dirty_folio().  That is obtained with
- * private_lock.
- *
- * try_to_free_buffers() is non-blocking.
- */
 static inline int buffer_busy(struct buffer_head *bh)
 {
 	return atomic_read(&bh->b_count) |
@@ -2916,6 +2896,30 @@ drop_buffers(struct folio *folio, struct buffer_head **buffers_to_free)
 	return false;
 }
 
+/**
+ * try_to_free_buffers: Release buffers attached to this folio.
+ * @folio: The folio.
+ *
+ * If any buffers are in use (dirty, under writeback, elevated refcount),
+ * no buffers will be freed.
+ *
+ * If the folio is dirty but all the buffers are clean then we need to
+ * be sure to mark the folio clean as well.  This is because the folio
+ * may be against a block device, and a later reattachment of buffers
+ * to a dirty folio will set *all* buffers dirty.  Which would corrupt
+ * filesystem data on the same device.
+ *
+ * The same applies to regular filesystem folios: if all the buffers are
+ * clean then we set the folio clean and proceed.  To do that, we require
+ * total exclusion from block_dirty_folio().  That is obtained with
+ * private_lock.
+ *
+ * Exclusion against try_to_free_buffers may be obtained by either
+ * locking the folio or by holding its mapping's private_lock.
+ *
+ * Context: Process context.  @folio must be locked.  Will not sleep.
+ * Return: true if all buffers attached to this folio were freed.
+ */
 bool try_to_free_buffers(struct folio *folio)
 {
 	struct address_space * const mapping = folio->mapping;
-- 
2.43.0