[PATCH 0/2] Update aops documentation

[PATCH 0/2] Update aops documentation

[Mel Gorman]

> > This patch adds an address_space operation that filesystems may
> > optionally use to check if a page is really dirty or really under
> > writeback.
> 
> address_space_operations methods are Documented in
> Documentation/filesystems/vfs.txt ;)

I could whinge that the aops docs are already out of date but fixing it
takes less time than coming up with excuses :)

 Documentation/filesystems/vfs.txt | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

-- 
1.8.1.4

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[PATCH 1/2] documentation: Update address_space_operations

[Mel Gorman]

The documentation for address_space_operations is partially out of date.

Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 Documentation/filesystems/vfs.txt | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index bc4b06b..a173cb7 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -549,12 +549,11 @@ struct address_space_operations
 -------------------------------
 
 This describes how the VFS can manipulate mapping of a file to page cache in
-your filesystem. As of kernel 2.6.22, the following members are defined:
+your filesystem. At the time of writing, the following members are defined:
 
 struct address_space_operations {
 	int (*writepage)(struct page *page, struct writeback_control *wbc);
 	int (*readpage)(struct file *, struct page *);
-	int (*sync_page)(struct page *);
 	int (*writepages)(struct address_space *, struct writeback_control *);
 	int (*set_page_dirty)(struct page *page);
 	int (*readpages)(struct file *filp, struct address_space *mapping,
@@ -576,6 +575,8 @@ struct address_space_operations {
 	/* migrate the contents of a page to the specified target */
 	int (*migratepage) (struct page *, struct page *);
 	int (*launder_page) (struct page *);
+	int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
+					unsigned long);
 	int (*error_remove_page) (struct mapping *mapping, struct page *page);
 	int (*swap_activate)(struct file *);
 	int (*swap_deactivate)(struct file *);
@@ -607,13 +608,6 @@ struct address_space_operations {
        In this case, the page will be relocated, relocked and if
        that all succeeds, ->readpage will be called again.
 
-  sync_page: called by the VM to notify the backing store to perform all
-  	queued I/O operations for a page. I/O operations for other pages
-	associated with this address_space object may also be performed.
-
-	This function is optional and is called only for pages with
-  	PG_Writeback set while waiting for the writeback to complete.
-
   writepages: called by the VM to write out pages associated with the
   	address_space object.  If wbc->sync_mode is WBC_SYNC_ALL, then
   	the writeback_control will specify a range of pages that must be
@@ -742,6 +736,11 @@ struct address_space_operations {
   	prevent redirtying the page, it is kept locked during the whole
 	operation.
 
+  is_partially_uptodate: Called by the VM when reading a file through the
+	pagecache when the underlying blocksize != pagesize. If the required
+	block is up to date then the read can complete without needing the IO
+	to bring the whole page up to date.
+
   error_remove_page: normally set to generic_error_remove_page if truncation
 	is ok for this address space. Used for memory failure handling.
 	Setting this implies you deal with pages going away under you,
-- 
1.8.1.4

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[PATCH 2/2] documentation: Document the is_dirty_writeback aops callback

[Mel Gorman]

Subject says it all.

Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 Documentation/filesystems/vfs.txt | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index a173cb7..6b26c75 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -577,6 +577,7 @@ struct address_space_operations {
 	int (*launder_page) (struct page *);
 	int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
 					unsigned long);
+	void (*is_dirty_writeback) (struct page *, bool *, bool *);
 	int (*error_remove_page) (struct mapping *mapping, struct page *page);
 	int (*swap_activate)(struct file *);
 	int (*swap_deactivate)(struct file *);
@@ -741,6 +742,15 @@ struct address_space_operations {
 	block is up to date then the read can complete without needing the IO
 	to bring the whole page up to date.
 
+  is_dirty_writeback: Called by the VM when attempting to reclaim a page.
+	The VM uses dirty and writeback information to determine if it needs
+	to stall to allow flushers a chance to complete some IO. Ordinarily
+	it can use PageDirty and PageWriteback but some filesystems have
+	more complex state (unstable pages in NFS prevent reclaim) or
+	do not set those flags due to locking problems (jbd). This callback
+	allows a filesystem to indicate to the VM if a page should be
+	treated as dirty or writeback for the purposes of stalling.
+
   error_remove_page: normally set to generic_error_remove_page if truncation
 	is ok for this address space. Used for memory failure handling.
 	Setting this implies you deal with pages going away under you,
-- 
1.8.1.4

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