Hi,
在 2025/08/26 15:54, Christoph Hellwig 写道:
On Tue, Aug 26, 2025 at 09:08:33AM +0800, Yu Kuai wrote:
在 2025/08/25 18:57, Christoph Hellwig 写道:
On Mon, Aug 25, 2025 at 05:36:55PM +0800, Yu Kuai wrote:
+ bio = bio_submit_split(bio,
+ zone->zone_end - bio->bi_iter.bi_sector,
+ &mddev->bio_set);
Do you know why raid0 and linear use mddev->bio_set for splitting
instead of their own split bio_sets like raid1/10/5? Is this safe?
I think it's not safe, as mddev->bio_split pool size is just 2, reuse
this pool to split multiple times before submitting will need greate
pool size to make this work.
By the way, do you think it's better to increate disk->bio_split pool
size to 4 and convert all mdraid internal split to use disk->bio_split
directly?
I don't really know where that magic number 4 or even the current number
comes from, but I think Jens might be amenable to a small increase with a
good explanation.
I was thinking we have to make sure issuing the allocated split bio
before allocating new bio, and that number is the safe limit that we can
allocated before issuing.
In case of recursive split, we can hold multiple split bio in
curent->bio_list, and with this set to handle split bio first, we can
gurantee we'll at most hold 3 split bios from mdraid:
- bio_split_to_limits(), for example, by max_sectors
- bio_split() by internal chunksize
- bio_split() by badblocks
That's why I said 4 should be safe :) If genddisk->bio_split can be
expanded to 4, all internal bio_split can be removed now.
Thanks,
Kuai
.
