Re: [PATCH] block: make queue limits workable in case of 64K PAGE_SIZE

[Ming Lei <ming.lei@redhat.com>]

On Fri, Jan 03, 2025 at 02:12:36PM -0800, Bart Van Assche wrote:
> On 1/2/25 6:01 PM, Ming Lei wrote:
> > But why does DMA segment size have to be >= PAGE_SIZE(4KB, 64KB)?
> 
> From the description of patch 5/8 of my patch series: "If the segment
> size is smaller than the page size there may be multiple segments per
> bvec even if a bvec only contains a single page." The current block
> layer implementation is based on the assumption that a single page
> fits in a single DMA segment. Please take a look at patch 5/8 of my
> patch series.

OK, I guess you agree it is one block layer constraint now, which
need to be relaxed for both big logical block size and >4k PAGE_SIZE.

Yes, your patch 5/8 is still needed.

> 
> > From the link, you have storage controllers with DMA segment size which
> > is less than 4K, which may never get supported by linux kernel.
> 
> As mentioned in the cover letter of that patch series, I came up with
> that patch series to support a DMA controller with max_segment_size of
> 4 KiB on a system with a PAGE_SIZE of 16 KiB.

Probably the conception of subpage need to avoid, because PAGE_SIZE is
config option, and not see strong reason to couple with fixed &
readable hardware properties with configurable kernel page size.


Thanks,
Ming