I agree that unwritten flag would be a better choice. I was thinking
to use it at the beginning but found it would be tricky to get it work.
See e.g. the unwritten flag usage in the current ext4_get_block.
I guess at some time later, we should clean up the buffer head
flag usage.
Jiaying
On Sun, Jan 17, 2010 at 6:21 AM, Aneesh Kumar K. V
<aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, 15 Jan 2010 14:30:11 -0500, "Theodore Ts'o" <tytso@xxxxxxx> wrote:
> > Allocate uninitialized extent before ext4 buffer write and
> > convert the extent to initialized after io completes.
> > The purpose is to make sure an extent can only be marked
> > initialized after it has been written with new data so
> > we can safely drop the i_mutex lock in ext4 DIO read without
> > exposing stale data. This helps to improve multi-thread DIO
> > read performance on high-speed disks.
> >
> > Skip the nobh and data=journal mount cases to make things simple for now.
> >
> > Signed-off-by: Jiaying Zhang <jiayingz@xxxxxxxxxx>
> > Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> > ---
> > fs/ext4/ext4.h | 12 +++++-
> > fs/ext4/ext4_jbd2.h | 24 ++++++++++++
> > fs/ext4/extents.c | 22 ++++++-----
> > fs/ext4/inode.c | 105 ++++++++++++++++++++++++++++++++++++++++----------
> > fs/ext4/super.c | 30 +++++++++++++--
> > 5 files changed, 157 insertions(+), 36 deletions(-)
> >
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index b1dcbb7..b8b4887 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -134,6 +134,7 @@ struct mpage_da_data {
> > int retval;
> > };
> > #define EXT4_IO_UNWRITTEN 0x1
> > +#define EXT4_IO_WRITTEN 0x2
> > typedef struct ext4_io_end {
> > struct list_head list; /* per-file finished AIO list */
> > struct inode *inode; /* file being written to */
> > @@ -370,7 +371,7 @@ struct ext4_new_group_data {
> > EXT4_GET_BLOCKS_CREATE_UNINIT_EXT)
> > /* Convert extent to initialized after IO complete */
> > #define EXT4_GET_BLOCKS_IO_CONVERT_EXT (EXT4_GET_BLOCKS_CONVERT|\
> > - EXT4_GET_BLOCKS_IO_CREATE_EXT)
> > + EXT4_GET_BLOCKS_CREATE_UNINIT_EXT)
> >
> > /*
> > * Flags used by ext4_free_blocks
> > @@ -761,6 +762,7 @@ struct ext4_inode_info {
> > #define EXT4_MOUNT_QUOTA 0x80000 /* Some quota option set */
> > #define EXT4_MOUNT_USRQUOTA 0x100000 /* "old" user quota */
> > #define EXT4_MOUNT_GRPQUOTA 0x200000 /* "old" group quota */
> > +#define EXT4_MOUNT_DIOREAD_NOLOCK 0x400000 /* Enable support for dio read nolocking */
> > #define EXT4_MOUNT_JOURNAL_CHECKSUM 0x800000 /* Journal checksums */
> > #define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT 0x1000000 /* Journal Async Commit */
> > #define EXT4_MOUNT_I_VERSION 0x2000000 /* i_version support */
> > @@ -1774,6 +1776,14 @@ static inline void set_bitmap_uptodate(struct buffer_head *bh)
> > set_bit(BH_BITMAP_UPTODATE, &(bh)->b_state);
> > }
> >
> > +/* BH_Uninit flag: blocks are allocated but uninitialized on disk */
> > +enum ext4_state_bits {
> > + BH_Uninit /* blocks are allocated but uninitialized on disk */
> > + = BH_JBDPrivateStart,
> > +};
> > +
> > +BUFFER_FNS(Uninit, uninit)
> > +
>
>
> I asked this in the last post. Why we need a new buffer head flag ?
> Why can't we use the unwritten flag ?
>
> -aneesh
>
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