> Walk through each allocation group and trim all free extents. It can be
> invoked through TRIM ioctl on the file system. The main idea is to
> provide a way to trim the whole file system if needed, since some SSD's
> may suffer from performance loss after the whole device was filled (it
> does not mean that fs is full!).
>
> It search for free extents in each allocation group. When the free
> extent is found, blocks are marked as used and then trimmed. Afterwards
> these blocks are marked as free in per-group bitmap.
>
> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> ---
> fs/ext3/balloc.c | 145 +++++++++++++++++++++++++++++++++++++++++++++++
> fs/ext3/super.c | 1 +
> include/linux/ext3_fs.h | 1 +
> 3 files changed, 147 insertions(+), 0 deletions(-)
>
> diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
> index a177122..bcee525 100644
> --- a/fs/ext3/balloc.c
> +++ b/fs/ext3/balloc.c
...
> + /**
> + * Allocate contiguous free extents by setting bits in the
> + * block bitmap
> + */
> + while (next < max
> + && !ext3_set_bit_atomic(sb_bgl_lock(sbi, group),
> + next, bh->b_data)) {
> + next++;
> + }
This is actually wrong. You completely ignore journalling here. You can't
just go and modify metadata buffer - other process can be modifying it as well
and writing it to disk and thus your changes will also get written. And if
a crash happens afterwards before the bitmap is written again, you'll get an
inconsistent filesystem.
Also you have to check whether the block isn't actually still used by a
running/committing transaction - look at fs/ext3/balloc.c:claim_block() to see
how you have to allocate free blocks.
All-in-all won't it be good enough to just freeze the fs, do the trimming,
and unfreeze it?
Honza
--
Jan Kara <jack@xxxxxxx>
SuSE CR Labs
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