On Fri, Aug 29, 2025 at 12:06:21PM +0200, David Hildenbrand wrote:
On 28.08.25 16:37, Lorenzo Stoakes wrote:
On Thu, Aug 28, 2025 at 12:01:10AM +0200, David Hildenbrand wrote:
Let's reject them early, which in turn makes folio_alloc_gigantic() reject them properly.
To avoid converting from order to nr_pages, let's just add MAX_FOLIO_ORDER and calculate MAX_FOLIO_NR_PAGES based on that.
Reviewed-by: Zi Yan ziy@nvidia.com Acked-by: SeongJae Park sj@kernel.org Signed-off-by: David Hildenbrand david@redhat.com
Some nits, but overall LGTM so:
Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
include/linux/mm.h | 6 ++++-- mm/page_alloc.c | 5 ++++- 2 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index 00c8a54127d37..77737cbf2216a 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2055,11 +2055,13 @@ static inline long folio_nr_pages(const struct folio *folio)
/* Only hugetlbfs can allocate folios larger than MAX_ORDER */ #ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE -#define MAX_FOLIO_NR_PAGES (1UL << PUD_ORDER) +#define MAX_FOLIO_ORDER PUD_ORDER #else -#define MAX_FOLIO_NR_PAGES MAX_ORDER_NR_PAGES +#define MAX_FOLIO_ORDER MAX_PAGE_ORDER #endif
+#define MAX_FOLIO_NR_PAGES (1UL << MAX_FOLIO_ORDER)
BIT()?
I don't think we want to use BIT whenever we convert from order -> folio -- which is why we also don't do that in other code.
It seems a bit arbitrary, like we open-code this (at risk of making a mistake) in some places but not others.
BIT() is nice in the context of flags and bitmaps, but not really in the context of converting orders to pages.
It's nice for setting a specific bit :)
One could argue that maybe one would want a order_to_pages() helper (that could use BIT() internally), but I am certainly not someone that would suggest that at this point ... :)
I mean maybe.
Anyway as I said none of this is massively important, the open-coding here is correct, just seems silly.
- /*
- compound_nr() returns the number of pages in this potentially compound
- page. compound_nr() can be called on a tail page, and is defined to
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index baead29b3e67b..426bc404b80cc 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6833,6 +6833,7 @@ static int __alloc_contig_verify_gfp_mask(gfp_t gfp_mask, gfp_t *gfp_cc_mask) int alloc_contig_range_noprof(unsigned long start, unsigned long end, acr_flags_t alloc_flags, gfp_t gfp_mask)
Funny btw th
{
- const unsigned int order = ilog2(end - start); unsigned long outer_start, outer_end; int ret = 0;
@@ -6850,6 +6851,9 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end, PB_ISOLATE_MODE_CMA_ALLOC : PB_ISOLATE_MODE_OTHER;
- if (WARN_ON_ONCE((gfp_mask & __GFP_COMP) && order > MAX_FOLIO_ORDER))
return -EINVAL;Possibly not worth it for a one off, but be nice to have this as a helper function, like:
static bool is_valid_order(gfp_t gfp_mask, unsigned int order) { return !(gfp_mask & __GFP_COMP) || order <= MAX_FOLIO_ORDER; }
Then makes this:
if (WARN_ON_ONCE(!is_valid_order(gfp_mask, order))) return -EINVAL;
Kinda self-documenting!
I don't like it -- especially forwarding __GFP_COMP.
is_valid_folio_order() to wrap the order check? Also not sure.
OK, it's not a big deal.
Can we have a comment explaining this though? As people might be confused as to why we check this here and not elsewhere.
So I'll leave it as is I think.
Right fine.
Thanks for all the review!
-- Cheers
David / dhildenb