Re: [PATCH v5 07/12] md: support to align bio to limits

Hi，

在 2026/1/19 14:47, Christoph Hellwig 写道:
> On Sun, Jan 18, 2026 at 07:40:23PM +0800, Yu Kuai wrote:
>> No, the chunk_sectors and io_opt are different, and align io to io_opt
>> is not a general idea, for now this is the only requirement in mdraid.
> The chunk size was added for (hardware) devices that require I/O split at
> a fixed granularity for performance reasons.  Which seems to e exactly
> what you want here.
>
> This has nothing to do with max_sectors.

For example, 32 disks raid5 array with chunksize=64k, currently the queue
limits are:

chunk_sectors = 64k
io_min = 64k
io_opt = 64 * 31k
max_sectors = 1M

It's correct to split I/O at 64k boundary to avoid performance issues, however
split at 64 *31k boundary is what we want to get best bandwidth.

So, if we simply changes chunk_sectors to 64 * 31k, it will be incorrect, because
64k boundary is still necessary for small IO.

So I'm not quite sure, are you suggesting following solution?

Add a max_chunk_sectors, and in this case it'll be 64 * 31k, for I/O:

1) First check and split to chunk_sectors boundary;
2) If I/O is already aligned to chunk_sectors, then check and split to
max_chunk_sectors boundary(BTW, this is what this set trying to do);

>
-- 
Thansk,
Kuai