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 [off-list ref] wrote:

quoted

On Fri, 13 May 2011, Vivek Haldar wrote:

quoted

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

quoted

Signed-off-by: Vivek Haldar <redacted>
---
 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);

--

--