gather_surplus_pages() pre-allocates hugetlb pages into the pool during mmap. Pass __GFP_ZERO so these pages are zeroed by the buddy allocator, and HPG_zeroed is set by alloc_surplus_hugetlb_folio.
Add bool *zeroed output to alloc_hugetlb_folio_reserve() so callers can check whether the pool page is known-zero. memfd's memfd_alloc_folio() uses this to skip the explicit folio_zero_user() when the page is already zero. This avoids redundant zeroing for memfd hugetlb pages that were pre-allocated into the pool and never mapped to userspace. Signed-off-by: Michael S. Tsirkin <[email protected]> Assisted-by: Claude:claude-opus-4-6 --- include/linux/hugetlb.h | 6 ++++-- mm/hugetlb.c | 11 +++++++++-- mm/memfd.c | 17 +++++++++++------ 3 files changed, 24 insertions(+), 10 deletions(-) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 094714c607f9..93bb06a33f57 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -713,7 +713,8 @@ struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, nodemask_t *nmask, gfp_t gfp_mask, bool allow_alloc_fallback); struct folio *alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid, - nodemask_t *nmask, gfp_t gfp_mask); + nodemask_t *nmask, gfp_t gfp_mask, + bool *zeroed); int hugetlb_add_to_page_cache(struct folio *folio, struct address_space *mapping, pgoff_t idx); @@ -1128,7 +1129,8 @@ static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, static inline struct folio * alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid, - nodemask_t *nmask, gfp_t gfp_mask) + nodemask_t *nmask, gfp_t gfp_mask, + bool *zeroed) { return NULL; } diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 4f0ed01f5b13..f02583b9faab 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2241,7 +2241,7 @@ struct folio *alloc_buddy_hugetlb_folio_with_mpol(struct hstate *h, } struct folio *alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid, - nodemask_t *nmask, gfp_t gfp_mask) + nodemask_t *nmask, gfp_t gfp_mask, bool *zeroed) { struct folio *folio; @@ -2257,6 +2257,12 @@ struct folio *alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid, h->resv_huge_pages--; spin_unlock_irq(&hugetlb_lock); + + if (zeroed && folio) { + *zeroed = folio_test_hugetlb_zeroed(folio); + folio_clear_hugetlb_zeroed(folio); + } + return folio; } @@ -2341,7 +2347,8 @@ static int gather_surplus_pages(struct hstate *h, long delta) * It is okay to use NUMA_NO_NODE because we use numa_mem_id() * down the road to pick the current node if that is the case. */ - folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h), + folio = alloc_surplus_hugetlb_folio(h, + htlb_alloc_mask(h) | __GFP_ZERO, NUMA_NO_NODE, &alloc_nodemask, USER_ADDR_NONE); if (!folio) { diff --git a/mm/memfd.c b/mm/memfd.c index 919c2a53eb96..b9b44ed54db5 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -90,20 +90,24 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx) if (nr_resv < 0) return ERR_PTR(nr_resv); + { + bool zeroed; + folio = alloc_hugetlb_folio_reserve(h, numa_node_id(), NULL, - gfp_mask); + gfp_mask, + &zeroed); if (folio) { u32 hash; /* - * Zero the folio to prevent information leaks to userspace. - * Use folio_zero_user() which is optimized for huge/gigantic - * pages. Pass 0 as addr_hint since this is not a faulting path - * and we don't have a user virtual address yet. + * Zero the folio to prevent information leaks to + * userspace. Skip if the pool page is known-zero + * (HPG_zeroed set during pool pre-allocation). */ - folio_zero_user(folio, 0); + if (!zeroed) + folio_zero_user(folio, 0); /* * Mark the folio uptodate before adding to page cache, @@ -139,6 +143,7 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx) hugetlb_unreserve_pages(inode, idx, idx + 1, 0); return ERR_PTR(err); } + } #endif return shmem_read_folio(memfd->f_mapping, idx); } -- MST
