Le mercredi 27 août 2008 à 17:14 -0400, Theodore Ts'o a écrit :
> This speeds up access to the journal by eliminating worst-case seeks
> from one end of the disk to another, which can be quite common in very
> fsync-intensive workloads if the file is located near the end of the
> disk, and the journal is located the beginning of the disk.
>
> In addition, this can help eliminate journal fragmentation when
> flex_bg is enabled, since the first block group has a large amount of
> metadata.
>
> Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> ---
> lib/ext2fs/mkjournal.c | 28 +++++++++++++++++++++++-----
> 1 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/lib/ext2fs/mkjournal.c b/lib/ext2fs/mkjournal.c
> index 3cae874..cd3df07 100644
> --- a/lib/ext2fs/mkjournal.c
> +++ b/lib/ext2fs/mkjournal.c
> @@ -198,6 +198,7 @@ errcode_t ext2fs_zero_blocks(ext2_filsys fs, blk_t blk, int num,
> struct mkjournal_struct {
> int num_blocks;
> int newblocks;
> + blk_t goal;
> blk_t blk_to_zero;
> int zero_count;
> char *buf;
> @@ -213,14 +214,13 @@ static int mkjournal_proc(ext2_filsys fs,
> {
> struct mkjournal_struct *es = (struct mkjournal_struct *) priv_data;
> blk_t new_blk;
> - static blk_t last_blk = 0;
> errcode_t retval;
>
> if (*blocknr) {
> - last_blk = *blocknr;
> + es->goal = *blocknr;
> return 0;
> }
> - retval = ext2fs_new_block(fs, last_blk, 0, &new_blk);
> + retval = ext2fs_new_block(fs, es->goal, 0, &new_blk);
> if (retval) {
> es->err = retval;
> return BLOCK_ABORT;
> @@ -258,8 +258,7 @@ static int mkjournal_proc(ext2_filsys fs,
> es->err = retval;
> return BLOCK_ABORT;
> }
> - *blocknr = new_blk;
> - last_blk = new_blk;
> + *blocknr = es->goal = new_blk;
> ext2fs_block_alloc_stats(fs, new_blk, +1);
>
> if (es->num_blocks == 0)
> @@ -276,6 +275,7 @@ static errcode_t write_journal_inode(ext2_filsys fs, ext2_ino_t journal_ino,
> blk_t size, int flags)
> {
> char *buf;
> + dgrp_t group, start, end, i;
> errcode_t retval;
> struct ext2_inode inode;
> struct mkjournal_struct es;
> @@ -298,6 +298,24 @@ static errcode_t write_journal_inode(ext2_filsys fs, ext2_ino_t journal_ino,
> es.err = 0;
> es.zero_count = 0;
>
> + /*
> + * Set the initial goal block to be roughly at the middle of
> + * the filesystem. Pick a group that has the largest number
> + * of free blocks.
> + */
> + group = ext2fs_group_of_blk(fs, (fs->super->s_blocks_count -
> + fs->super->s_first_data_block) / 2);
> + start = (group > 0) ? group-1 : group;
> + end = ((group+1) < fs->group_desc_count) ? group+1 : group;
With 512 groups by flex group, meta-datas for a single flex-group are 8
groups long ! If we have no luck and there are a bunch of groups
occupied by meta-datas at the middle of the filesystem, we should
slightly increase the number of groups scanned to find a completely free
group.
> + group = start;
> + for (i=start+1; i <= end; i++)
> + if (fs->group_desc[i].bg_free_blocks_count >
> + fs->group_desc[group].bg_free_blocks_count)
> + group = i;
This is ok if the journal file has the default size, but not optimal if
it's bigger than one group.
> +
> + es.goal = (fs->super->s_blocks_per_group * group) +
> + fs->super->s_first_data_block;
> +
> retval = ext2fs_block_iterate2(fs, journal_ino, BLOCK_FLAG_APPEND,
> 0, mkjournal_proc, &es);
> if (es.err) {
--
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