On Mon, 16 May 2011, Vivek Haldar wrote:
> EXT4_GET_BLOCKS_* and EXT4_MB_HINT_* are different flag spaces and
> should not be mixed. ext4_ext_map_blocks should not be using
> EXT4_MB_HINT_*, it only uses EXT4_GET_BLOCKS_*.
Agh, yes you're right of course, somehow I just missed that
ext4_map_blocks() take separate flag argument and EXT4_GET_* flag might
use the same bit as EXT4_MB_HINT_NOPREALLOC. Sorry.
Thanks!
-Lukas
>
> On Mon, May 16, 2011 at 2:39 AM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote:
> > On Fri, 13 May 2011, Vivek Haldar wrote:
> >
> >> Currently, an fallocate request of size slightly larger than a power of
> >> 2 is turned into two block requests, each a power of 2, with the extra
> >> blocks pre-allocated for future use. When an application calls
> >> fallocate, it already has an idea about how large the file may grow so
> >> there is usually little benefit to reserve extra blocks on the
> >> preallocation list. This reduces disk fragmentation.
> >>
> >> Tested: fsstress. Also verified manually that fallocat'ed files are
> >> contiguously laid out with this change (whereas without it they begin at
> >> power-of-2 boundaries, leaving blocks in between). CPU usage of
> >> fallocate is not appreciably higher. In a tight fallocate loop, CPU
> >> usage hovers between 5%-8% with this change, and 5%-7% without it.
> >
> > Hi Vivek,
> >
> > the patch looks good, but I do not understand why you are introducing
> > new #define when you can simply use EXT4_MB_HINT_NOPREALLOC and then in
> > the ext4_ext_map_blocks() just do :
> >
> > ar.flags |= (flags & EXT4_MB_HINT_NOPREALLOC)
> >
> > and you do not need to introduce new condition. Am I missing something ?
> >
> > Thanks!
> > -Lukas
> >
> >>
> >> Signed-off-by: Vivek Haldar <haldar@xxxxxxxxxx>
> >> ---
> >> fs/ext4/ext4.h | 2 ++
> >> fs/ext4/extents.c | 5 ++++-
> >> 2 files changed, 6 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> >> index 076c5d2..e606d34 100644
> >> --- a/fs/ext4/ext4.h
> >> +++ b/fs/ext4/ext4.h
> >> @@ -512,6 +512,8 @@ struct ext4_new_group_data {
> >> /* Convert extent to initialized after IO complete */
> >> #define EXT4_GET_BLOCKS_IO_CONVERT_EXT (EXT4_GET_BLOCKS_CONVERT|\
> >> EXT4_GET_BLOCKS_CREATE_UNINIT_EXT)
> >> + /* Don't normalize when fallocat'ing */
> >> +#define EXT4_GET_BLOCKS_NO_NORMALIZE 0x0020
> >>
> >> /*
> >> * Flags used by ext4_free_blocks
> >> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> >> index e363f21..f02dd52 100644
> >> --- a/fs/ext4/extents.c
> >> +++ b/fs/ext4/extents.c
> >> @@ -3304,6 +3304,8 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
> >> else
> >> /* disable in-core preallocation for non-regular files */
> >> ar.flags = 0;
> >> + if (flags & EXT4_GET_BLOCKS_NO_NORMALIZE)
> >> + ar.flags |= EXT4_MB_HINT_NOPREALLOC;
> >> newblock = ext4_mb_new_blocks(handle, &ar, &err);
> >> if (!newblock)
> >> goto out2;
> >> @@ -3549,7 +3551,8 @@ retry:
> >> break;
> >> }
> >> ret = ext4_map_blocks(handle, inode, &map,
> >> - EXT4_GET_BLOCKS_CREATE_UNINIT_EXT);
> >> + EXT4_GET_BLOCKS_CREATE_UNINIT_EXT |
> >> + EXT4_GET_BLOCKS_NO_NORMALIZE);
> >> if (ret <= 0) {
> >> #ifdef EXT4FS_DEBUG
> >> WARN_ON(ret <= 0);
> >>
> >
> > --
> >
>
>
>
>
--
