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Date: Wed, 8 May 2013 15:08:26 +0800
From: Zheng Liu <gnehzuil.liu@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 22/29] ext4: Defer clearing of PageWriteback after extent
conversion
On Mon, Apr 08, 2013 at 11:32:27PM +0200, Jan Kara wrote:
> Currently PageWriteback bit gets cleared from put_io_page() called from
> ext4_end_bio(). This is somewhat inconvenient as extent tree is not
> fully updated at that time (unwritten extents are not marked as written)
> so we cannot read the data back yet. This design was dictated by lock
> ordering as we cannot start a transaction while PageWriteback bit is set
> (we could easily deadlock with ext4_da_writepages()). But now that we
> use transaction reservation for extent conversion, locking issues are
> solved and we can move PageWriteback bit clearing after extent
> conversion is done. As a result we can remove wait for unwritt en extent
> conversion from ext4_sync_file() because it already implicitely happe ns
> through wait_on_page_writeback().
>
> We implement deferring of PageWriteback clearing by queueing completed
> bios to appropriate io_end and processing all the pages when io_end is
> going to be freed instead of at the moment ext4_io_end() is called.
>
> Signed-off-by: Jan Kara <jack@...e.cz>
Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
Regards,
- Zheng
> ---
> fs/ext4/ext4.h | 2 +
> fs/ext4/fsync.c | 4 --
> fs/ext4/page-io.c | 132 +++++++++++++++++++++++++++++------------------------
> 3 files changed, 74 insertions(+), 64 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index a594a94..2b0dd9a 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -190,6 +190,8 @@ typedef struct ext4_io_end {
> handle_t *handle; /* handle reserved for extent
> * conversion */
> struct inode *inode; /* file being written to */
> + struct bio *bio; /* Linked list of completed
> + * bios covering the extent */
> unsigned int flag; /* unwritten or not */
> loff_t offset; /* offset in the file */
> ssize_t size; /* size of the extent */
> diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
> index 3278e64..e02ba1b 100644
> --- a/fs/ext4/fsync.c
> +++ b/fs/ext4/fsync.c
> @@ -132,10 +132,6 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> if (inode->i_sb->s_flags & MS_RDONLY)
> goto out;
>
> - ret = ext4_flush_unwritten_io(inode);
> - if (ret < 0)
> - goto out;
> -
> if (!journal) {
> ret = __sync_inode(inode, datasync);
> if (!ret && !hlist_empty(&inode->i_dentry))
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index 8bff3b3..2967794 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -51,14 +51,83 @@ void ext4_ioend_wait(struct inode *inode)
> wait_event(*wq, (atomic_read(&EXT4_I(inode)->i_ioend_count) == 0));
> }
>
> +/*
> + * 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_finish_bio(struct bio *bio)
> +{
> + int i;
> + int error = !test_bit(BIO_UPTODATE, &bio->bi_flags);
> +
> + for (i = 0; i < bio->bi_vcnt; i++) {
> + struct bio_vec *bvec = &bio->bi_io_vec[i];
> + struct page *page = bvec->bv_page;
> + struct buffer_head *bh, *head;
> + unsigned bio_start = bvec->bv_offset;
> + unsigned bio_end = bio_start + bvec->bv_len;
> + unsigned under_io = 0;
> + unsigned long flags;
> +
> + if (!page)
> + continue;
> +
> + if (error) {
> + SetPageError(page);
> + set_bit(AS_EIO, &page->mapping->flags);
> + }
> + bh = head = page_buffers(page);
> + /*
> + * We check all buffers in the page under BH_Uptodate_Lock
> + * to avoid races with other end io clearing async_write flags
> + */
> + local_irq_save(flags);
> + bit_spin_lock(BH_Uptodate_Lock, &head->b_state);
> + do {
> + if (bh_offset(bh) < bio_start ||
> + bh_offset(bh) + bh->b_size > bio_end) {
> + if (buffer_async_write(bh))
> + under_io++;
> + continue;
> + }
> + clear_buffer_async_write(bh);
> + if (error)
> + buffer_io_error(bh);
> + } while ((bh = bh->b_this_page) != head);
> + bit_spin_unlock(BH_Uptodate_Lock, &head->b_state);
> + local_irq_restore(flags);
> + if (!under_io)
> + end_page_writeback(page);
> + }
> +}
> +
> static void ext4_release_io_end(ext4_io_end_t *io_end)
> {
> + struct bio *bio, *next_bio;
> +
> BUG_ON(!list_empty(&io_end->list));
> BUG_ON(io_end->flag & EXT4_IO_END_UNWRITTEN);
> WARN_ON(io_end->handle);
>
> if (atomic_dec_and_test(&EXT4_I(io_end->inode)->i_ioend_count))
> wake_up_all(ext4_ioend_wq(io_end->inode));
> +
> + for (bio = io_end->bio; bio; bio = next_bio) {
> + next_bio = bio->bi_private;
> + ext4_finish_bio(bio);
> + bio_put(bio);
> + }
> if (io_end->flag & EXT4_IO_END_DIRECT)
> inode_dio_done(io_end->inode);
> if (io_end->iocb)
> @@ -254,76 +323,20 @@ ext4_io_end_t *ext4_get_io_end(ext4_io_end_t *io_end)
> return io_end;
> }
>
> -/*
> - * 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 inode *inode;
> - int i;
> - int blocksize;
> sector_t bi_sector = bio->bi_sector;
>
> BUG_ON(!io_end);
> inode = io_end->inode;
> - blocksize = 1 << inode->i_blkbits;
> - bio->bi_private = NULL;
> bio->bi_end_io = NULL;
> + /* Link bio into list hanging from io_end */
> + bio->bi_private = io_end->bio;
> + io_end->bio = bio;
> if (test_bit(BIO_UPTODATE, &bio->bi_flags))
> error = 0;
> - for (i = 0; i < bio->bi_vcnt; i++) {
> - struct bio_vec *bvec = &bio->bi_io_vec[i];
> - struct page *page = bvec->bv_page;
> - struct buffer_head *bh, *head;
> - unsigned bio_start = bvec->bv_offset;
> - unsigned bio_end = bio_start + bvec->bv_len;
> - unsigned under_io = 0;
> - unsigned long flags;
> -
> - if (!page)
> - continue;
> -
> - if (error) {
> - SetPageError(page);
> - set_bit(AS_EIO, &page->mapping->flags);
> - }
> - bh = head = page_buffers(page);
> - /*
> - * We check all buffers in the page under BH_Uptodate_Lock
> - * to avoid races with other end io clearing async_write flags
> - */
> - local_irq_save(flags);
> - bit_spin_lock(BH_Uptodate_Lock, &head->b_state);
> - do {
> - if (bh_offset(bh) < bio_start ||
> - bh_offset(bh) + blocksize > bio_end) {
> - if (buffer_async_write(bh))
> - under_io++;
> - continue;
> - }
> - clear_buffer_async_write(bh);
> - if (error)
> - buffer_io_error(bh);
> - } while ((bh = bh->b_this_page) != head);
> - bit_spin_unlock(BH_Uptodate_Lock, &head->b_state);
> - local_irq_restore(flags);
> - if (!under_io)
> - end_page_writeback(page);
> - }
> - bio_put(bio);
>
> if (error) {
> io_end->flag |= EXT4_IO_END_ERROR;
> @@ -335,7 +348,6 @@ static void ext4_end_bio(struct bio *bio, int error)
> (unsigned long long)
> bi_sector >> (inode->i_blkbits - 9));
> }
> -
> ext4_put_io_end_defer(io_end);
> }
>
> --
> 1.7.1
>
> --
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