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Message-Id: <20200201151240.24082-5-willy@infradead.org>
Date: Sat, 1 Feb 2020 07:12:32 -0800
From: Matthew Wilcox <willy@...radead.org>
To: linux-fsdevel@...r.kernel.org
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linux-btrfs@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
linux-xfs@...r.kernel.org, cluster-devel@...hat.com,
ocfs2-devel@....oracle.com
Subject: [PATCH v4 04/12] mm: Add readahead address space operation
From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
This replaces ->readpages with a saner interface:
- Return the number of pages not read instead of an ignored error code.
- Pages are already in the page cache when ->readahead is called.
- Implementation looks up the pages in the page cache instead of
having them passed in a linked list.
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Cc: linux-btrfs@...r.kernel.org
Cc: linux-erofs@...ts.ozlabs.org
Cc: linux-ext4@...r.kernel.org
Cc: linux-f2fs-devel@...ts.sourceforge.net
Cc: linux-xfs@...r.kernel.org
Cc: cluster-devel@...hat.com
Cc: ocfs2-devel@....oracle.com
---
Documentation/filesystems/locking.rst | 7 ++++++-
Documentation/filesystems/vfs.rst | 14 ++++++++++++++
include/linux/fs.h | 2 ++
include/linux/pagemap.h | 12 ++++++++++++
mm/readahead.c | 13 ++++++++++++-
5 files changed, 46 insertions(+), 2 deletions(-)
diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 5057e4d9dcd1..3d10729caf44 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);
+ unsigned (*readahead)(struct file *, struct address_space *,
+ pgoff_t start, unsigned nr_pages);
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:
+readahead: yes, unlocks
+readpages: no
write_begin: locks the page exclusive
write_end: yes, unlocks exclusive
bmap:
@@ -295,6 +298,8 @@ the request handler (/dev/loop).
->readpage() unlocks the page, either synchronously or via I/O
completion.
+->readahead() unlocks the pages like ->readpage().
+
->readpages() populates the pagecache with the passed pages and starts
I/O against them. They come unlocked upon I/O completion.
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 7d4d09dd5e6d..c2bc345f2169 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);
+ unsigned (*readahead)(struct file *filp, struct address_space *mapping,
+ pgoff_t start, unsigned nr_pages);
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 +783,18 @@ 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. The pages are consecutive in the page cache and
+ are locked. The implementation should decrement the page
+ refcount after attempting I/O on each page. Usually the
+ page will be unlocked by the I/O completion handler. If the
+ function does not attempt I/O on some pages, return the number
+ of pages which were not read so the caller can unlock the pages
+ for you. Set PageUptodate if the I/O completes successfully.
+ Setting PageError on any page will be ignored; simply unlock
+ the page if an I/O error occurs.
+
``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 41584f50af0d..3bfc142e7d10 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -375,6 +375,8 @@ struct address_space_operations {
*/
int (*readpages)(struct file *filp, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages);
+ unsigned (*readahead)(struct file *, struct address_space *,
+ pgoff_t start, unsigned nr_pages);
int (*write_begin)(struct file *, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ccb14b6a16b5..a2cf007826f2 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -630,6 +630,18 @@ static inline int add_to_page_cache(struct page *page,
return error;
}
+/*
+ * Only call this from a ->readahead implementation.
+ */
+static inline
+struct page *readahead_page(struct address_space *mapping, pgoff_t index)
+{
+ struct page *page = xa_load(&mapping->i_pages, index);
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+
+ return page;
+}
+
static inline unsigned long dir_pages(struct inode *inode)
{
return (unsigned long)(inode->i_size + PAGE_SIZE - 1) >>
diff --git a/mm/readahead.c b/mm/readahead.c
index 7daef0038b14..b2ed0baf3a5d 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -121,7 +121,18 @@ static void read_pages(struct address_space *mapping, struct file *filp,
blk_start_plug(&plug);
- if (mapping->a_ops->readpages) {
+ if (mapping->a_ops->readahead) {
+ unsigned left = mapping->a_ops->readahead(filp, mapping,
+ start, nr_pages);
+
+ while (left) {
+ struct page *page = readahead_page(mapping,
+ start + nr_pages - left);
+ unlock_page(page);
+ put_page(page);
+ left--;
+ }
+ } else if (mapping->a_ops->readpages) {
mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
/* Clean up the remaining pages */
put_pages_list(pages);
--
2.24.1
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