From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
This will replace ->readpages with a saner interface:
- No return type (errors are ignored for read ahead anyway)
- Pages are already in the page cache when ->readpages is called
- Pages are passed in a pagevec instead of a linked list
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
Documentation/filesystems/locking.rst | 8 +++++-
Documentation/filesystems/vfs.rst | 9 ++++++
include/linux/fs.h | 3 ++
mm/readahead.c | 40 ++++++++++++++++++++++++++-
4 files changed, 58 insertions(+), 2 deletions(-)
diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 5057e4d9dcd1..1e2f1186fd1a 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -239,6 +239,8 @@ prototypes::
int (*readpage)(struct file *, struct page *);
int (*writepages)(struct address_space *, struct writeback_control *);
int (*set_page_dirty)(struct page *page);
+ int (*readahead)(struct file *, struct address_space *,
+ struct pagevec *, pgoff_t index);
int (*readpages)(struct file *filp, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages);
int (*write_begin)(struct file *, struct address_space *mapping,
@@ -271,7 +273,8 @@ writepage: yes, unlocks (see below)
readpage: yes, unlocks
writepages:
set_page_dirty no
-readpages:
+readpages: no
+readahead: yes, unlocks
write_begin: locks the page exclusive
write_end: yes, unlocks exclusive
bmap:
@@ -298,6 +301,9 @@ completion.
->readpages() populates the pagecache with the passed pages and starts
I/O against them. They come unlocked upon I/O completion.
+->readahead() starts I/O against the pages. They come unlocked upon
+I/O completion.
+
->writepage() is used for two purposes: for "memory cleansing" and for
"sync". These are quite different operations and the behaviour may differ
depending upon the mode.
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 7d4d09dd5e6d..63d0f0dbbf9c 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -706,6 +706,8 @@ cache in your filesystem. The following members are defined:
int (*readpage)(struct file *, struct page *);
int (*writepages)(struct address_space *, struct writeback_control *);
int (*set_page_dirty)(struct page *page);
+ int (*readahead)(struct file *, struct address_space *,
+ struct pagevec *, pgoff_t index);
int (*readpages)(struct file *filp, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages);
int (*write_begin)(struct file *, struct address_space *mapping,
@@ -781,6 +783,13 @@ cache in your filesystem. The following members are defined:
If defined, it should set the PageDirty flag, and the
PAGECACHE_TAG_DIRTY tag in the radix tree.
+``readahead``
+ called by the VM to read pages associated with the address_space
+ object. This is essentially a vector version of readpage.
+ Instead of just one page, several pages are requested.
+ Since this is readahead, attempt to start I/O on each page and
+ let the I/O completion path set errors on the page.
+
``readpages``
called by the VM to read pages associated with the address_space
object. This is essentially just a vector version of readpage.
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 98e0349adb52..2769f89666fb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -52,6 +52,7 @@ struct hd_geometry;
struct iovec;
struct kiocb;
struct kobject;
+struct pagevec;
struct pipe_inode_info;
struct poll_table_struct;
struct kstatfs;
@@ -375,6 +376,8 @@ struct address_space_operations {
*/
int (*readpages)(struct file *filp, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages);
+ void (*readahead)(struct file *, struct address_space *,
+ struct pagevec *, pgoff_t offset);
int (*write_begin)(struct file *, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
diff --git a/mm/readahead.c b/mm/readahead.c
index 76a70a4406b5..2fe0974173ea 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -123,7 +123,45 @@ static unsigned read_pages(struct address_space *mapping, struct file *filp,
struct page *page;
unsigned int nr_pages = pagevec_count(pvec);
- if (mapping->a_ops->readpages) {
+ if (mapping->a_ops->readahead) {
+ /*
+ * When we remove support for ->readpages, we'll call
+ * add_to_page_cache_lru() in the parent and all this
+ * grot goes away.
+ */
+ unsigned char first = pvec->first;
+ unsigned char saved_nr = pvec->nr;
+ pgoff_t base = offset;
+ pagevec_for_each(pvec, page) {
+ if (!add_to_page_cache_lru(page, mapping, offset++,
+ gfp)) {
+ unsigned char saved_first = pvec->first;
+
+ pvec->nr = pvec->first - 1;
+ pvec->first = first;
+ mapping->a_ops->readahead(filp, mapping, pvec,
+ base + first);
+ first = pvec->nr + 1;
+ pvec->nr = saved_nr;
+ pvec->first = saved_first;
+
+ put_page(page);
+ }
+ }
+ pvec->first = first;
+ offset = base + first;
+ mapping->a_ops->readahead(filp, mapping, pvec, offset);
+ /*
+ * Ideally the implementation would at least attempt to
+ * start I/O against all the pages, but there are times
+ * when it makes more sense to just give up. Take care
+ * of any un-attempted pages here.
+ */
+ pagevec_for_each(pvec, page) {
+ unlock_page(page);
+ put_page(page);
+ }
+ } else if (mapping->a_ops->readpages) {
LIST_HEAD(pages);
pagevec_for_each(pvec, page) {
--
2.24.1
