Add PG_zeroed (aliased to PG_private) to track pages whose contents are known to be zero. Exclude __PG_ZEROED from PAGE_FLAGS_CHECK_AT_PREP so the allocator does not BUG when encountering zeroed pages on the free list.
Signed-off-by: Michael S. Tsirkin <[email protected]> Assisted-by: Claude:claude-opus-4-6 Assisted-by: cursor-agent:GPT-5.4-xhigh --- include/linux/page-flags.h | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index f7a0e4af0c73..f87ecb740e7f 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -157,6 +157,9 @@ enum pageflags { */ PG_fscache = PG_private_2, /* page backed by cache */ + /* Page contents are known to be zero (host-zeroed or balloon) */ + PG_zeroed = PG_private, + /* XEN */ /* Pinned in Xen as a read-only pagetable page. */ PG_pinned = PG_owner_priv_1, @@ -687,6 +690,14 @@ FOLIO_FLAG_FALSE(idle) */ __PAGEFLAG(Reported, reported, PF_NO_COMPOUND) +/* + * PageZeroed() tracks pages whose contents are known to be zero. + * Set on free-list pages by the balloon driver or page reporting. + * The allocator uses this to skip redundant zeroing. + */ +__PAGEFLAG(Zeroed, zeroed, PF_NO_COMPOUND) +#define __PG_ZEROED (1UL << PG_zeroed) + #ifdef CONFIG_MEMORY_HOTPLUG PAGEFLAG(VmemmapSelfHosted, vmemmap_self_hosted, PF_ANY) #else @@ -1209,7 +1220,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page) * alloc-free cycle to prevent from reusing the page. */ #define PAGE_FLAGS_CHECK_AT_PREP \ - ((PAGEFLAGS_MASK & ~__PG_HWPOISON) | LRU_GEN_MASK | LRU_REFS_MASK) + ((PAGEFLAGS_MASK & ~(__PG_HWPOISON | __PG_ZEROED)) | LRU_GEN_MASK | LRU_REFS_MASK) /* * Flags stored in the second page of a compound page. They may overlap -- MST
