ext4: use bio layer instead of buffer layer in mpage_da_submit_io

Call the block I/O layer directly instad of going through the buffer
layer.  This should give us much better performance and scalability,
as well as lowering our CPU utilization when doing buffered writeback.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

6 files changed, 489 insertions, 109 deletions

diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
index 8867b2a1e5fe..c947e36eda6c 100644
--- a/fs/ext4/Makefile
+++ b/fs/ext4/Makefile
@@ -4,7 +4,7 @@
 
 obj-$(CONFIG_EXT4_FS) += ext4.o
 
-ext4-y  := balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o \
+ext4-y  := balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \
                 ioctl.o namei.o super.o symlink.o hash.o resize.o extents.o \
                 ext4_jbd2.o migrate.o mballoc.o block_validity.o move_extent.o
 
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 22833691e98c..ca9fda64dd4f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -168,7 +168,20 @@ struct mpage_da_data {
         int pages_written;
         int retval;
 };
-#define EXT4_IO_UNWRITTEN       0x1
+
+/*
+ * Flags for ext4_io_end->flags
+ */
+#define EXT4_IO_END_UNWRITTEN   0x0001
+#define EXT4_IO_END_ERROR       0x0002
+
+struct ext4_io_page {
+        struct page     *p_page;
+        int             p_count;
+};
+
+#define MAX_IO_PAGES 128
+
 typedef struct ext4_io_end {
         struct list_head        list;           /* per-file finished IO list */
         struct inode            *inode;         /* file being written to */
@@ -179,8 +192,18 @@ typedef struct ext4_io_end {
         struct work_struct      work;           /* data work queue */
         struct kiocb            *iocb;          /* iocb struct for AIO */
         int                     result;         /* error value for AIO */
+        int                     num_io_pages;
+        struct ext4_io_page     *pages[MAX_IO_PAGES];
 } ext4_io_end_t;
 
+struct ext4_io_submit {
+        int                     io_op;
+        struct bio              *io_bio;
+        ext4_io_end_t           *io_end;
+        struct ext4_io_page     *io_page;
+        sector_t                io_next_block;
+};
+
 /*
  * Special inodes numbers
  */
@@ -2044,6 +2067,17 @@ extern int ext4_move_extents(struct file *o_filp, struct file *d_filp,
                              __u64 start_orig, __u64 start_donor,
                              __u64 len, __u64 *moved_len);
 
+/* page-io.c */
+extern int __init init_ext4_pageio(void);
+extern void exit_ext4_pageio(void);
+extern void ext4_free_io_end(ext4_io_end_t *io);
+extern ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags);
+extern int ext4_end_io_nolock(ext4_io_end_t *io);
+extern void ext4_io_submit(struct ext4_io_submit *io);
+extern int ext4_bio_write_page(struct ext4_io_submit *io,
+                               struct page *page,
+                               int len,
+                               struct writeback_control *wbc);
 
 /* BH_Uninit flag: blocks are allocated but uninitialized on disk */
 enum ext4_state_bits {
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index a0e623055955..a1e20c8c4e0c 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3202,7 +3202,7 @@ ext4_ext_handle_uninitialized_extents(handle_t *handle, struct inode *inode,
                  * completed
                  */
                 if (io)
-                        io->flag = EXT4_IO_UNWRITTEN;
+                        io->flag = EXT4_IO_END_UNWRITTEN;
                 else
                         ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
                 if (ext4_should_dioread_nolock(inode))
@@ -3494,7 +3494,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
                  */
                 if ((flags & EXT4_GET_BLOCKS_PRE_IO)) {
                         if (io)
-                                io->flag = EXT4_IO_UNWRITTEN;
+                                io->flag = EXT4_IO_END_UNWRITTEN;
                         else
                                 ext4_set_inode_state(inode,
                                                      EXT4_STATE_DIO_UNWRITTEN);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c65d647378f9..58604fe11f4f 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2016,8 +2016,10 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd,
         struct buffer_head *bh, *page_bufs = NULL;
         int journal_data = ext4_should_journal_data(inode);
         sector_t pblock = 0, cur_logical = 0;
+        struct ext4_io_submit io_submit;
 
         BUG_ON(mpd->next_page <= mpd->first_page);
+        memset(&io_submit, 0, sizeof(io_submit));
         /*
          * We need to start from the first_page to the next_page - 1
          * to make sure we also write the mapped dirty buffer_heads.
@@ -2109,16 +2111,16 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd,
                                 /* mark the buffer_heads as dirty & uptodate */
                                 block_commit_write(page, 0, len);
 
-                        if (journal_data && PageChecked(page))
+                        /*
+                         * Delalloc doesn't support data journalling,
+                         * but eventually maybe we'll lift this
+                         * restriction.
+                         */
+                        if (unlikely(journal_data && PageChecked(page)))
                                 err = __ext4_journalled_writepage(page, len);
-                        else if (buffer_uninit(page_bufs)) {
-                                ext4_set_bh_endio(page_bufs, inode);
-                                err = block_write_full_page_endio(page,
-                                        noalloc_get_block_write,
-                                        mpd->wbc, ext4_end_io_buffer_write);
-                        } else
-                                err = block_write_full_page(page,
-                                            noalloc_get_block_write, mpd->wbc);
+                        else
+                                err = ext4_bio_write_page(&io_submit, page,
+                                                          len, mpd->wbc);
 
                         if (!err)
                                 mpd->pages_written++;
@@ -2131,6 +2133,7 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd,
                 }
                 pagevec_release(&pvec);
         }
+        ext4_io_submit(&io_submit);
         return ret;
 }
 
@@ -3426,15 +3429,6 @@ ext4_readpages(struct file *file, struct address_space *mapping,
         return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
 }
 
-static void ext4_free_io_end(ext4_io_end_t *io)
-{
-        BUG_ON(!io);
-        if (io->page)
-                put_page(io->page);
-        iput(io->inode);
-        kfree(io);
-}
-
 static void ext4_invalidatepage_free_endio(struct page *page, unsigned long offset)
 {
         struct buffer_head *head, *bh;
@@ -3640,68 +3634,6 @@ static void dump_completed_IO(struct inode * inode)
 }
 
 /*
- * check a range of space and convert unwritten extents to written.
- */
-static int ext4_end_io_nolock(ext4_io_end_t *io)
-{
-        struct inode *inode = io->inode;
-        loff_t offset = io->offset;
-        ssize_t size = io->size;
-        int ret = 0;
-
-        ext4_debug("ext4_end_io_nolock: io 0x%p from inode %lu,list->next 0x%p,"
-                   "list->prev 0x%p\n",
-                   io, inode->i_ino, io->list.next, io->list.prev);
-
-        if (list_empty(&io->list))
-                return ret;
-
-        if (io->flag != EXT4_IO_UNWRITTEN)
-                return ret;
-
-        ret = ext4_convert_unwritten_extents(inode, offset, size);
-        if (ret < 0) {
-                printk(KERN_EMERG "%s: failed to convert unwritten"
-                        "extents to written extents, error is %d"
-                        " io is still on inode %lu aio dio list\n",
-                       __func__, ret, inode->i_ino);
-                return ret;
-        }
-
-        if (io->iocb)
-                aio_complete(io->iocb, io->result, 0);
-        /* clear the DIO AIO unwritten flag */
-        io->flag = 0;
-        return ret;
-}
-
-/*
- * work on completed aio dio IO, to convert unwritten extents to extents
- */
-static void ext4_end_io_work(struct work_struct *work)
-{
-        ext4_io_end_t           *io = container_of(work, ext4_io_end_t, work);
-        struct inode            *inode = io->inode;
-        struct ext4_inode_info  *ei = EXT4_I(inode);
-        unsigned long           flags;
-        int                     ret;
-
-        mutex_lock(&inode->i_mutex);
-        ret = ext4_end_io_nolock(io);
-        if (ret < 0) {
-                mutex_unlock(&inode->i_mutex);
-                return;
-        }
-
-        spin_lock_irqsave(&ei->i_completed_io_lock, flags);
-        if (!list_empty(&io->list))
-                list_del_init(&io->list);
-        spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
-        mutex_unlock(&inode->i_mutex);
-        ext4_free_io_end(io);
-}
-
-/*
  * This function is called from ext4_sync_file().
  *
  * When IO is completed, the work to convert unwritten extents to
@@ -3756,28 +3688,6 @@ int flush_completed_IO(struct inode *inode)
         return (ret2 < 0) ? ret2 : 0;
 }
 
-static ext4_io_end_t *ext4_init_io_end (struct inode *inode, gfp_t flags)
-{
-        ext4_io_end_t *io = NULL;
-
-        io = kmalloc(sizeof(*io), flags);
-
-        if (io) {
-                igrab(inode);
-                io->inode = inode;
-                io->flag = 0;
-                io->offset = 0;
-                io->size = 0;
-                io->page = NULL;
-                io->iocb = NULL;
-                io->result = 0;
-                INIT_WORK(&io->work, ext4_end_io_work);
-                INIT_LIST_HEAD(&io->list);
-        }
-
-        return io;
-}
-
 static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
                             ssize_t size, void *private, int ret,
                             bool is_async)
@@ -3797,7 +3707,7 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
                   size);
 
         /* if not aio dio with unwritten extents, just free io and return */
-        if (io_end->flag != EXT4_IO_UNWRITTEN){
+        if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
                 ext4_free_io_end(io_end);
                 iocb->private = NULL;
 out:
@@ -3842,7 +3752,7 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
                 goto out;
         }
 
-        io_end->flag = EXT4_IO_UNWRITTEN;
+        io_end->flag = EXT4_IO_END_UNWRITTEN;
         inode = io_end->inode;
 
         /* Add the io_end to per-inode completed io list*/
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
new file mode 100644
index 000000000000..b972ca50f851
--- /dev/null
+++ b/fs/ext4/page-io.c
@@ -0,0 +1,430 @@
+/*
+ * linux/fs/ext4/page-io.c
+ *
+ * This contains the new page_io functions for ext4
+ *
+ * Written by Theodore Ts'o, 2010.
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/time.h>
+#include <linux/jbd2.h>
+#include <linux/highuid.h>
+#include <linux/pagemap.h>
+#include <linux/quotaops.h>
+#include <linux/string.h>
+#include <linux/buffer_head.h>
+#include <linux/writeback.h>
+#include <linux/pagevec.h>
+#include <linux/mpage.h>
+#include <linux/namei.h>
+#include <linux/uio.h>
+#include <linux/bio.h>
+#include <linux/workqueue.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+
+#include "ext4_jbd2.h"
+#include "xattr.h"
+#include "acl.h"
+#include "ext4_extents.h"
+
+static struct kmem_cache *io_page_cachep, *io_end_cachep;
+
+int __init init_ext4_pageio(void)
+{
+        io_page_cachep = KMEM_CACHE(ext4_io_page, SLAB_RECLAIM_ACCOUNT);
+        if (io_page_cachep == NULL)
+                return -ENOMEM;
+        io_end_cachep = KMEM_CACHE(ext4_io_end, SLAB_RECLAIM_ACCOUNT);
+        if (io_page_cachep == NULL) {
+                kmem_cache_destroy(io_page_cachep);
+                return -ENOMEM;
+        }
+
+        return 0;
+}
+
+void exit_ext4_pageio(void)
+{
+        kmem_cache_destroy(io_end_cachep);
+        kmem_cache_destroy(io_page_cachep);
+}
+
+void ext4_free_io_end(ext4_io_end_t *io)
+{
+        int i;
+
+        BUG_ON(!io);
+        if (io->page)
+                put_page(io->page);
+        for (i = 0; i < io->num_io_pages; i++) {
+                if (--io->pages[i]->p_count == 0) {
+                        struct page *page = io->pages[i]->p_page;
+
+                        end_page_writeback(page);
+                        put_page(page);
+                        kmem_cache_free(io_page_cachep, io->pages[i]);
+                }
+        }
+        io->num_io_pages = 0;
+        iput(io->inode);
+        kmem_cache_free(io_end_cachep, io);
+}
+
+/*
+ * check a range of space and convert unwritten extents to written.
+ */
+int ext4_end_io_nolock(ext4_io_end_t *io)
+{
+        struct inode *inode = io->inode;
+        loff_t offset = io->offset;
+        ssize_t size = io->size;
+        int ret = 0;
+
+        ext4_debug("ext4_end_io_nolock: io 0x%p from inode %lu,list->next 0x%p,"
+                   "list->prev 0x%p\n",
+                   io, inode->i_ino, io->list.next, io->list.prev);
+
+        if (list_empty(&io->list))
+                return ret;
+
+        if (!(io->flag & EXT4_IO_END_UNWRITTEN))
+                return ret;
+
+        ret = ext4_convert_unwritten_extents(inode, offset, size);
+        if (ret < 0) {
+                printk(KERN_EMERG "%s: failed to convert unwritten "
+                        "extents to written extents, error is %d "
+                        "io is still on inode %lu aio dio list\n",
+                       __func__, ret, inode->i_ino);
+                return ret;
+        }
+
+        if (io->iocb)
+                aio_complete(io->iocb, io->result, 0);
+        /* clear the DIO AIO unwritten flag */
+        io->flag &= ~EXT4_IO_END_UNWRITTEN;
+        return ret;
+}
+
+/*
+ * work on completed aio dio IO, to convert unwritten extents to extents
+ */
+static void ext4_end_io_work(struct work_struct *work)
+{
+        ext4_io_end_t           *io = container_of(work, ext4_io_end_t, work);
+        struct inode            *inode = io->inode;
+        struct ext4_inode_info  *ei = EXT4_I(inode);
+        unsigned long           flags;
+        int                     ret;
+
+        mutex_lock(&inode->i_mutex);
+        ret = ext4_end_io_nolock(io);
+        if (ret < 0) {
+                mutex_unlock(&inode->i_mutex);
+                return;
+        }
+
+        spin_lock_irqsave(&ei->i_completed_io_lock, flags);
+        if (!list_empty(&io->list))
+                list_del_init(&io->list);
+        spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
+        mutex_unlock(&inode->i_mutex);
+        ext4_free_io_end(io);
+}
+
+ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)
+{
+        ext4_io_end_t *io = NULL;
+
+        io = kmem_cache_alloc(io_end_cachep, flags);
+        if (io) {
+                memset(io, 0, sizeof(*io));
+                io->inode = igrab(inode);
+                BUG_ON(!io->inode);
+                INIT_WORK(&io->work, ext4_end_io_work);
+                INIT_LIST_HEAD(&io->list);
+        }
+        return io;
+}
+
+/*
+ * Print an buffer I/O error compatible with the fs/buffer.c.  This
+ * provides compatibility with dmesg scrapers that look for a specific
+ * buffer I/O error message.  We really need a unified error reporting
+ * structure to userspace ala Digital Unix's uerf system, but it's
+ * probably not going to happen in my lifetime, due to LKML politics...
+ */
+static void buffer_io_error(struct buffer_head *bh)
+{
+        char b[BDEVNAME_SIZE];
+        printk(KERN_ERR "Buffer I/O error on device %s, logical block %llu\n",
+                        bdevname(bh->b_bdev, b),
+                        (unsigned long long)bh->b_blocknr);
+}
+
+static void ext4_end_bio(struct bio *bio, int error)
+{
+        ext4_io_end_t *io_end = bio->bi_private;
+        struct workqueue_struct *wq;
+        struct inode *inode;
+        unsigned long flags;
+        ext4_fsblk_t err_block;
+        int i;
+
+        BUG_ON(!io_end);
+        inode = io_end->inode;
+        bio->bi_private = NULL;
+        bio->bi_end_io = NULL;
+        if (test_bit(BIO_UPTODATE, &bio->bi_flags))
+                error = 0;
+        err_block = bio->bi_sector >> (inode->i_blkbits - 9);
+        bio_put(bio);
+
+        if (!(inode->i_sb->s_flags & MS_ACTIVE)) {
+                pr_err("sb umounted, discard end_io request for inode %lu\n",
+                        io_end->inode->i_ino);
+                ext4_free_io_end(io_end);
+                return;
+        }
+
+        if (error) {
+                io_end->flag |= EXT4_IO_END_ERROR;
+                ext4_warning(inode->i_sb, "I/O error writing to inode %lu "
+                             "(offset %llu size %ld starting block %llu)",
+                             inode->i_ino,
+                             (unsigned long long) io_end->offset,
+                             (long) io_end->size,
+                             (unsigned long long) err_block);
+        }
+
+        for (i = 0; i < io_end->num_io_pages; i++) {
+                struct page *page = io_end->pages[i]->p_page;
+                struct buffer_head *bh, *head;
+                int partial_write = 0;
+
+                head = page_buffers(page);
+                if (error)
+                        SetPageError(page);
+                BUG_ON(!head);
+                if (head->b_size == PAGE_CACHE_SIZE)
+                        clear_buffer_dirty(head);
+                else {
+                        loff_t offset;
+                        loff_t io_end_offset = io_end->offset + io_end->size;
+
+                        offset = (sector_t) page->index << PAGE_CACHE_SHIFT;
+                        bh = head;
+                        do {
+                                if ((offset >= io_end->offset) &&
+                                    (offset+bh->b_size <= io_end_offset)) {
+                                        if (error)
+                                                buffer_io_error(bh);
+
+                                        clear_buffer_dirty(bh);
+                                }
+                                if (buffer_delay(bh))
+                                        partial_write = 1;
+                                else if (!buffer_mapped(bh))
+                                        clear_buffer_dirty(bh);
+                                else if (buffer_dirty(bh))
+                                        partial_write = 1;
+                                offset += bh->b_size;
+                                bh = bh->b_this_page;
+                        } while (bh != head);
+                }
+
+                if (--io_end->pages[i]->p_count == 0) {
+                        struct page *page = io_end->pages[i]->p_page;
+
+                        end_page_writeback(page);
+                        put_page(page);
+                        kmem_cache_free(io_page_cachep, io_end->pages[i]);
+                }
+
+                /*
+                 * If this is a partial write which happened to make
+                 * all buffers uptodate then we can optimize away a
+                 * bogus readpage() for the next read(). Here we
+                 * 'discover' whether the page went uptodate as a
+                 * result of this (potentially partial) write.
+                 */
+                if (!partial_write)
+                        SetPageUptodate(page);
+        }
+
+        io_end->num_io_pages = 0;
+
+        /* Add the io_end to per-inode completed io list*/
+        spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
+        list_add_tail(&io_end->list, &EXT4_I(inode)->i_completed_io_list);
+        spin_unlock_irqrestore(&EXT4_I(inode)->i_completed_io_lock, flags);
+
+        wq = EXT4_SB(inode->i_sb)->dio_unwritten_wq;
+        /* queue the work to convert unwritten extents to written */
+        queue_work(wq, &io_end->work);
+}
+
+void ext4_io_submit(struct ext4_io_submit *io)
+{
+        struct bio *bio = io->io_bio;
+
+        if (bio) {
+                bio_get(io->io_bio);
+                submit_bio(io->io_op, io->io_bio);
+                BUG_ON(bio_flagged(io->io_bio, BIO_EOPNOTSUPP));
+                bio_put(io->io_bio);
+        }
+        io->io_bio = 0;
+        io->io_op = 0;
+        io->io_end = 0;
+}
+
+static int io_submit_init(struct ext4_io_submit *io,
+                          struct inode *inode,
+                          struct writeback_control *wbc,
+                          struct buffer_head *bh)
+{
+        ext4_io_end_t *io_end;
+        struct page *page = bh->b_page;
+        int nvecs = bio_get_nr_vecs(bh->b_bdev);
+        struct bio *bio;
+
+        io_end = ext4_init_io_end(inode, GFP_NOFS);
+        if (!io_end)
+                return -ENOMEM;
+        do {
+                bio = bio_alloc(GFP_NOIO, nvecs);
+                nvecs >>= 1;
+        } while (bio == NULL);
+
+        bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
+        bio->bi_bdev = bh->b_bdev;
+        bio->bi_private = io->io_end = io_end;
+        bio->bi_end_io = ext4_end_bio;
+
+        io_end->inode = inode;
+        io_end->offset = (page->index << PAGE_CACHE_SHIFT) + bh_offset(bh);
+
+        io->io_bio = bio;
+        io->io_op = (wbc->sync_mode == WB_SYNC_ALL ?
+                        WRITE_SYNC_PLUG : WRITE);
+        io->io_next_block = bh->b_blocknr;
+        return 0;
+}
+
+static int io_submit_add_bh(struct ext4_io_submit *io,
+                            struct ext4_io_page *io_page,
+                            struct inode *inode,
+                            struct writeback_control *wbc,
+                            struct buffer_head *bh)
+{
+        ext4_io_end_t *io_end;
+        int ret;
+
+        if (buffer_new(bh)) {
+                clear_buffer_new(bh);
+                unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
+        }
+
+        if (!buffer_mapped(bh) || buffer_delay(bh)) {
+                if (!buffer_mapped(bh))
+                        clear_buffer_dirty(bh);
+                if (io->io_bio)
+                        ext4_io_submit(io);
+                return 0;
+        }
+
+        if (io->io_bio && bh->b_blocknr != io->io_next_block) {
+submit_and_retry:
+                ext4_io_submit(io);
+        }
+        if (io->io_bio == NULL) {
+                ret = io_submit_init(io, inode, wbc, bh);
+                if (ret)
+                        return ret;
+        }
+        io_end = io->io_end;
+        if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
+            (io_end->pages[io_end->num_io_pages-1] != io_page))
+                goto submit_and_retry;
+        if (buffer_uninit(bh))
+                io->io_end->flag |= EXT4_IO_END_UNWRITTEN;
+        io->io_end->size += bh->b_size;
+        io->io_next_block++;
+        ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));
+        if (ret != bh->b_size)
+                goto submit_and_retry;
+        if ((io_end->num_io_pages == 0) ||
+            (io_end->pages[io_end->num_io_pages-1] != io_page)) {
+                io_end->pages[io_end->num_io_pages++] = io_page;
+                io_page->p_count++;
+        }
+        return 0;
+}
+
+int ext4_bio_write_page(struct ext4_io_submit *io,
+                        struct page *page,
+                        int len,
+                        struct writeback_control *wbc)
+{
+        struct inode *inode = page->mapping->host;
+        unsigned block_start, block_end, blocksize;
+        struct ext4_io_page *io_page;
+        struct buffer_head *bh, *head;
+        int ret = 0;
+
+        blocksize = 1 << inode->i_blkbits;
+
+        BUG_ON(PageWriteback(page));
+        set_page_writeback(page);
+        ClearPageError(page);
+
+        io_page = kmem_cache_alloc(io_page_cachep, GFP_NOFS);
+        if (!io_page) {
+                set_page_dirty(page);
+                unlock_page(page);
+                return -ENOMEM;
+        }
+        io_page->p_page = page;
+        io_page->p_count = 0;
+        get_page(page);
+
+        for (bh = head = page_buffers(page), block_start = 0;
+             bh != head || !block_start;
+             block_start = block_end, bh = bh->b_this_page) {
+                block_end = block_start + blocksize;
+                if (block_start >= len) {
+                        clear_buffer_dirty(bh);
+                        set_buffer_uptodate(bh);
+                        continue;
+                }
+                ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
+                if (ret) {
+                        /*
+                         * We only get here on ENOMEM.  Not much else
+                         * we can do but mark the page as dirty, and
+                         * better luck next time.
+                         */
+                        set_page_dirty(page);
+                        break;
+                }
+        }
+        unlock_page(page);
+        /*
+         * If the page was truncated before we could do the writeback,
+         * or we had a memory allocation error while trying to write
+         * the first buffer head, we won't have submitted any pages for
+         * I/O.  In that case we need to make sure we've cleared the
+         * PageWriteback bit from the page to prevent the system from
+         * wedging later on.
+         */
+        if (io_page->p_count == 0) {
+                put_page(page);
+                end_page_writeback(page);
+                kmem_cache_free(io_page_cachep, io_page);
+        }
+        return ret;
+}
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 8a24e9be7cb0..e13b3c3534d7 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4769,9 +4769,12 @@ static int __init init_ext4_fs(void)
         int err;
 
         ext4_check_flag_values();
-        err = init_ext4_system_zone();
+        err = init_ext4_pageio();
         if (err)
                 return err;
+        err = init_ext4_system_zone();
+        if (err)
+                goto out5;
         ext4_kset = kset_create_and_add("ext4", NULL, fs_kobj);
         if (!ext4_kset)
                 goto out4;
@@ -4812,6 +4815,8 @@ out3:
         kset_unregister(ext4_kset);
 out4:
         exit_ext4_system_zone();
+out5:
+        exit_ext4_pageio();
         return err;
 }
 
@@ -4827,6 +4832,7 @@ static void __exit exit_ext4_fs(void)
         remove_proc_entry("fs/ext4", NULL);
         kset_unregister(ext4_kset);
         exit_ext4_system_zone();
+        exit_ext4_pageio();
 }
 
 MODULE_AUTHOR("Remy Card, Stephen Tweedie, Andrew Morton, Andreas Dilger, Theodore Ts'o and others");