Re: [PATCH] block: add bio_iov_iter_nvecs for figuring out nr_vecs

On 08/12/2020 01:50, Ming Lei wrote:

On Mon, Dec 07, 2020 at 06:07:39PM +0000, Pavel Begunkov wrote:

quoted

On 01/12/2020 12:06, Ming Lei wrote:

quoted

Pavel reported that iov_iter_npages is a bit heavy in case of bvec
iter.

Turns out it isn't necessary to iterate every page in the bvec iter,
and we call iov_iter_npages() just for figuring out how many bio
vecs need to be allocated. And we can simply map each vector in bvec iter
to bio's vec, so just return iter->nr_segs from bio_iov_iter_nvecs() for
bvec iter.

Also rename local variable 'nr_pages' as 'nr_vecs' which exactly matches its
real usage.

This patch is based on Mathew's post:

Tried this, the system didn't boot + discovered a filesystem blowned after
booting with a stable kernel. That's on top of 4498a8536c816 ("block: use
an xarray for disk->part_tbl"), which works fine. Ideas?

I guess it is caused by Christoph's "store a pointer to the block_device in struct bio (again)"
which has been reverted in for-5.11/block.

I'd suggest to run your test against the latest for-5.11/block one more time.

Ah, now it works, thanks for the idea
Unfortunately, I haven't got any logs, it died pretty early

-- 
Pavel Begunkov