Re: [PATCH v2 4/4] mm/vmalloc: Hugepage vmalloc mappings

[Nicholas Piggin <npiggin@gmail.com>]

Excerpts from Matthew Wilcox's message of April 13, 2020 11:41 pm:
> On Mon, Apr 13, 2020 at 10:53:03PM +1000, Nicholas Piggin wrote:
>> +static int vmap_pages_range_noflush(unsigned long start, unsigned long end,
>> +				    pgprot_t prot, struct page **pages,
>> +				    unsigned int page_shift)
>> +{
>> +	if (page_shift == PAGE_SIZE) {
> 
> ... I think you meant 'page_shift == PAGE_SHIFT'

Thanks, good catch. I obviously didn't test the fallback path (the
other path works for small pages, it just goes one at a time).

> Overall I like this series, although it's a bit biased towards CPUs
> which have page sizes which match PMD/PUD sizes.  It doesn't offer the
> possibility of using 64kB page sizes on ARM, for example.

No, it's just an incremental step on existing huge vmap stuff in
tree, so such a thing would be out of scope.

> But it's a
> step in the right direction.
> 

I don't know about moving kernel maps away from a generic Linux page
table format. I quite like moving to it and making it as generic as
possible.

On the other hand, I also would like to make some arch-specific
allowances for certain special cases that may not fit within the
standard page table format, but it might be a much more specific and
limited interface than the general vmalloc stuff.

Thanks,
Nick