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SubjectRe: [PATCH v1 12/54] dm: limit the max bio size as BIO_MAX_PAGES * PAGE_SIZE
On Tue, Dec 27 2016 at 10:56am -0500,
Ming Lei <tom.leiming@gmail.com> wrote:

> For BIO based DM, some targets aren't ready for dealing with
> bigger incoming bio than 1Mbyte, such as crypt target.
>
> Signed-off-by: Ming Lei <tom.leiming@gmail.com>
> ---
> drivers/md/dm.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 3086da5664f3..6139bf7623f7 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -899,7 +899,16 @@ int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)
> return -EINVAL;
> }
>
> - ti->max_io_len = (uint32_t) len;
> + /*
> + * BIO based queue uses its own splitting. When multipage bvecs
> + * is switched on, size of the incoming bio may be too big to
> + * be handled in some targets, such as crypt.
> + *
> + * When these targets are ready for the big bio, we can remove
> + * the limit.
> + */
> + ti->max_io_len = min_t(uint32_t, len,
> + (BIO_MAX_PAGES * PAGE_SIZE));
>
> return 0;
> }
> --
> 2.7.4

dm_set_target_max_io_len() is already meant to be called by the .ctr
hook for each DM target. So why not just have the dm-crypt target (and
other targets if needed) pass your reduced $len?

That way only targets that need to be fixed (e.g. dm-crypt) impose this
limit.

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