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>

1 files changed, 430 insertions, 0 deletions

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;
+}