Re: [PATCH V2] block: make segment size limit workable for > 4K PAGE_SIZE

[John Garry <john.g.garry@xxxxxxxxxx>]

On 13/02/2025 11:33, Ming Lei wrote:
> > I think that we need to take max_segment_size into account in
> > blk_queue_max_guaranteed_bio(), like:
> >
> > static unsigned int blk_queue_max_guaranteed_bio(struct queue_limits *lim)
> > {
> > 	unsigned int max_segments = min(BIO_MAX_VECS, lim->max_segments);
> > 	unsigned int length;
> >
> > 	length = min(max_segments, 2) * lim->logical_block_size;
> > 	if (max_segments > 2)
> > 		length += (max_segments - 2) * min(PAGE_SIZE, lim->max_segment_size);
> >
> > 	return length;
> > }
> >
> > Note that blk_queue_max_guaranteed_bio() is only really relevant to dio, so
> > assumes that the iov_iter follows the bdev dio rules
> It can't work because ITER_UBUF from pwritev2(iovcnt=1) is virtually-contiguous,

Right

> and the middle segment size has to be PAGE_SIZE.

I would have thought that those PAGE_SIZE-sized middle iovecs should be 
split into multiple segments, no?

Thanks,
John