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Date: Fri, 15 Jun 2012 17:29:10 +0800
From: Robin Dong <hao.bigrat@...il.com>
To: Zheng Liu <gnehzuil.liu@...il.com>
Cc: linux-ext4@...r.kernel.org, Tao Ma <tm@....ma>,
Eric Sandeen <sandeen@...hat.com>,
Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [RFC][PATCH v2 2/3] ext4: add a new flag for ext4_map_blocks
2012/6/14 Zheng Liu <gnehzuil.liu@...il.com>:
> From: Zheng Liu <wenqing.lz@...bao.com>
>
> EXT4_GET_BLOCKS_NO_LOCK flag is added to indicate that we don't need to acquire
> i_data_sem lock in ext4_map_blocks. Meanwhile, it lets _ext4_get_block do not
> start a new journal because when we do a overwrite dio, there is no any
> metadata that needs to be modified.
>
> We define a new function called ext4_get_block_write_nolock, which is used in
> dio overwrite nolock. In this function, it doesn't try to acquire i_data_sem
> lock and doesn't start a new journal as it does a lookup.
>
> CC: Tao Ma <tm@....ma>
> CC: Eric Sandeen <sandeen@...hat.com>
> Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
> ---
> fs/ext4/ext4.h | 2 +
> fs/ext4/inode.c | 59 +++++++++++++++++++++++++++++++++++++++++++++---------
> 2 files changed, 51 insertions(+), 10 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index cfc4e01..d1a2b1e 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -571,6 +571,8 @@ enum {
> #define EXT4_GET_BLOCKS_NO_NORMALIZE 0x0040
> /* Request will not result in inode size update (user for fallocate) */
> #define EXT4_GET_BLOCKS_KEEP_SIZE 0x0080
> + /* Do not take i_data_sem locking in ext4_map_blocks */
> +#define EXT4_GET_BLOCKS_NO_LOCK 0x0100
>
> /*
> * Flags used by ext4_free_blocks
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 02bc8cb..9a714ff 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -544,7 +544,8 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
> * Try to see if we can get the block without requesting a new
> * file system block.
> */
> - down_read((&EXT4_I(inode)->i_data_sem));
> + if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
> + down_read((&EXT4_I(inode)->i_data_sem));
> if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
> retval = ext4_ext_map_blocks(handle, inode, map, flags &
> EXT4_GET_BLOCKS_KEEP_SIZE);
> @@ -552,7 +553,8 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
> retval = ext4_ind_map_blocks(handle, inode, map, flags &
> EXT4_GET_BLOCKS_KEEP_SIZE);
> }
> - up_read((&EXT4_I(inode)->i_data_sem));
> + if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
> + up_read((&EXT4_I(inode)->i_data_sem));
>
> if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
> int ret = check_block_validity(inode, map);
> @@ -2818,6 +2820,32 @@ static int ext4_get_block_write(struct inode *inode, sector_t iblock,
> EXT4_GET_BLOCKS_IO_CREATE_EXT);
> }
>
> +static int ext4_get_block_write_nolock(struct inode *inode, sector_t iblock,
> + struct buffer_head *bh_result, int create)
> +{
> + handle_t *handle = ext4_journal_current_handle();
> + struct ext4_map_blocks map;
> + int ret = 0;
> +
> + ext4_debug("ext4_get_block_write_nolock: inode %lu, create flag %d\n",
> + inode->i_ino, create);
> +
> + create = EXT4_GET_BLOCKS_NO_LOCK;
May be better to change the variable "create" to "flags"
> +
> + map.m_lblk = iblock;
> + map.m_len = bh_result->b_size >> inode->i_blkbits;
> +
> + ret = ext4_map_blocks(handle, inode, &map, create);
> + if (ret > 0) {
> + map_bh(bh_result, inode->i_sb, map.m_pblk);
> + bh_result->b_state = (bh_result->b_state & ~EXT4_MAP_FLAGS) |
> + map.m_flags;
> + bh_result->b_size = inode->i_sb->s_blocksize * map.m_len;
> + ret = 0;
> + }
> + return ret;
> +}
> +
> static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
> ssize_t size, void *private, int ret,
> bool is_async)
> @@ -2966,6 +2994,8 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
>
> loff_t final_size = offset + count;
> if (rw == WRITE && final_size <= inode->i_size) {
> + int overwrite = 0;
> +
> /*
> * We could direct write to holes and fallocate.
> *
> @@ -3005,13 +3035,22 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> EXT4_I(inode)->cur_aio_dio = iocb->private;
> }
>
> - ret = __blockdev_direct_IO(rw, iocb, inode,
> - inode->i_sb->s_bdev, iov,
> - offset, nr_segs,
> - ext4_get_block_write,
> - ext4_end_io_dio,
> - NULL,
> - DIO_LOCKING);
> + if (overwrite)
> + ret = __blockdev_direct_IO(rw, iocb, inode,
> + inode->i_sb->s_bdev, iov,
> + offset, nr_segs,
> + ext4_get_block_write_nolock,
> + ext4_end_io_dio,
> + NULL,
> + 0);
> + else
> + ret = __blockdev_direct_IO(rw, iocb, inode,
> + inode->i_sb->s_bdev, iov,
> + offset, nr_segs,
> + ext4_get_block_write,
> + ext4_end_io_dio,
> + NULL,
> + DIO_LOCKING);
> if (iocb->private)
> EXT4_I(inode)->cur_aio_dio = NULL;
> /*
> @@ -3031,7 +3070,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> if (ret != -EIOCBQUEUED && ret <= 0 && iocb->private) {
> ext4_free_io_end(iocb->private);
> iocb->private = NULL;
> - } else if (ret > 0 && ext4_test_inode_state(inode,
> + } else if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
> EXT4_STATE_DIO_UNWRITTEN)) {
> int err;
> /*
> --
> 1.7.4.1
>
> --
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--
--
Best Regard
Robin Dong
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