Re: brd in a memdesc world

[Jens Axboe <axboe@kernel.dk>]

On 3/12/24 11:40 AM, Matthew Wilcox wrote:
> Hi Jens,
> 
> I'm looking for an architecture-level decision on what the brd driver
> should look like once struct page has been shrunk to a minimal size
> (more detail at https://kernelnewbies.org/MatthewWilcox/Memdescs )
> 
> Currently brd uses page->index as a debugging check.  In the memdesc
> future, struct page has no members (you could store a small amount of
> information in it, but I'm not willing to commit to more than a few bits).
> 
> brd doesn't use anything else from struct page, as far as I can tell.
> It just calls kmap_atomic() / __free_page() / flush_dcache_page() (and
> it doesn't need to call flush_dcache_page() because you can't mmap the
> pages in the brd's array).
> 
> Now if you have plans to, eg, support page migration, you're going to need
> a bit more infrastructure than just allocating pages, but for what you
> have at the moment, just removing the debugging checks that page->index ==
> idx would make you entirely compatible with the memdesc future.
> 
> Any problem with that?

As far as I can recall, I haven't seen that debugging trigger anything
in forever. So fine to kill it, imho.

-- 
Jens Axboe