On 30/08/2023 16:07, Matthew Wilcox wrote:
> On Wed, Aug 30, 2023 at 10:50:11AM +0100, Ryan Roberts wrote:
>> +++ b/include/asm-generic/tlb.h
>> @@ -246,11 +246,11 @@ struct mmu_gather_batch {
>> struct mmu_gather_batch *next;
>> unsigned int nr;
>> unsigned int max;
>> - struct page *pages[];
>> + struct pfn_range folios[];
>
> I think it's dangerous to call this 'folios' as it lets you think that
> each entry is a single folio. But as I understand this patch, you can
> coagulate contiguous ranges across multiple folios.
No that's not quite the case; each contiguous range only ever spans a *single*
folio. If there are 2 contiguous folios, they will be represented as separate
ranges. This is done so that we can subsequently do the per-folio operations
without having to figure out how many folios are within each range - one range =
one (contiguous part of a) folio.
On naming, I was calling this variable "ranges" in v1 but thought folios was
actually clearer. How about "folio_regions"?
>
>> -void free_pages_and_swap_cache(struct page **pages, int nr)
>> +void free_folios_and_swap_cache(struct pfn_range *folios, int nr)
>> {
>> lru_add_drain();
>> for (int i = 0; i < nr; i++)
>> - free_swap_cache(pages[i]);
>> - release_pages(pages, nr);
>> + free_swap_cache(pfn_to_page(folios[i].start));
>
> ... but here, you only put the swapcache for the first folio covered by
> the range, not for each folio.
Yes that's intentional - one range only ever covers one folio, so I only need to
call free_swap_cache() once for the folio. Unless I've misunderstood and
free_swap_cache() is actually decrementing a reference count and needs to be
called for every page? (but it doesn't look like that in the code).
>
>> + folios_put_refs(folios, nr);
>
> It's kind of confusing to have folios_put() which takes a struct folio *
> and then folios_put_refs() which takes a struct pfn_range *.
> pfn_range_put()?
I think it's less confusing if you know that each pfn_range represents a single
contig range of pages within a *single* folio. pfn_range_put() would make it
sound like its ok to pass a pfn_range that spans multiple folios (this would
break). I could rename `struct pfn_range` to `struct sub_folio` or something
like that. Would that help make the semantic clearer?
