Re: [PATCH][RESEND] btrfs: fix search key advancing condition

[Naohiro Aota]

Hello, list.

Could any one take a look at on this? I believe this is a issue slowing
down ioctl(BTRFS_IOC_TREE_SEARCH) if the target key is missing.

On Tue, Jun 30, 2015 at 11:25 AM, Naohiro Aota <naota@xxxxxxxxx> wrote:
> The search key advancing condition used in copy_to_sk() is loose. It can
> advance the key even if it reaches sk->max_*: e.g. when the max key = (512,
> 1024, -1) and the current key = (512, 1025, 10), it increments the
> offset by 1, continues hopeless search from (512, 1025, 11). This issue
> make ioctl() to take unexpectedly long time scanning all the leaf a blocks
> one by one.
>
> This commit fix the problem using standard way of key comparison:
> btrfs_comp_cpu_keys()
>
> Signed-off-by: Naohiro Aota <naota@xxxxxxxxx>
> ---
>  fs/btrfs/ioctl.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 1c22c65..07dc01d 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1932,6 +1932,7 @@ static noinline int copy_to_sk(struct btrfs_root *root,
>         u64 found_transid;
>         struct extent_buffer *leaf;
>         struct btrfs_ioctl_search_header sh;
> +       struct btrfs_key test;
>         unsigned long item_off;
>         unsigned long item_len;
>         int nritems;
> @@ -2015,12 +2016,17 @@ static noinline int copy_to_sk(struct btrfs_root *root,
>         }
>  advance_key:
>         ret = 0;
> -       if (key->offset < (u64)-1 && key->offset < sk->max_offset)
> +       test.objectid = sk->max_objectid;
> +       test.type = sk->max_type;
> +       test.offset = sk->max_offset;
> +       if (btrfs_comp_cpu_keys(key, &test) >= 0)
> +               ret = 1;
> +       else if (key->offset < (u64)-1)
>                 key->offset++;
> -       else if (key->type < (u8)-1 && key->type < sk->max_type) {
> +       else if (key->type < (u8)-1) {
>                 key->offset = 0;
>                 key->type++;
> -       } else if (key->objectid < (u64)-1 && key->objectid < sk->max_objectid) {
> +       } else if (key->objectid < (u64)-1) {
>                 key->offset = 0;
>                 key->type = 0;
>                 key->objectid++;
> --
> 2.4.4
>
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