On 12/3/24 08:59, Muchun Song wrote: > > >> On Dec 3, 2024, at 10:32, Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote: >> >> The HugeTLB order check against __NR_USED_SUBPAGE is required only when >> HUGETLB_PAGE_OPTIMIZE_VMEMMAP is enabled. Hence BUG_ON() trigger should >> happen only when applicable. >> >> Cc: Muchun Song <muchun.song@xxxxxxxxx> >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >> Cc: Oscar Salvador <osalvador@xxxxxxx> >> Cc: linux-mm@xxxxxxxxx >> Cc: linux-kernel@xxxxxxxxxxxxxxx >> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> >> --- >> This patch applies on v6.13-rc1 >> >> Changes in V2: >> >> - Fixed #ifdef with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP per Oscar >> >> Changes in V1: >> >> https://lore.kernel.org/all/20241202090728.78935-1-anshuman.khandual@xxxxxxx/ >> >> mm/hugetlb.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index ea2ed8e301ef..e6a5b21e3578 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -4513,11 +4513,13 @@ void __init hugetlb_add_hstate(unsigned int order) >> struct hstate *h; >> unsigned long i; >> >> - if (size_to_hstate(PAGE_SIZE << order)) { >> + if (size_to_hstate(PAGE_SIZE << order)) >> return; >> - } >> + >> BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE); >> +#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP >> BUG_ON(order < order_base_2(__NR_USED_SUBPAGE)); > > Hi Anshuman, > > __NR_USED_SUBPAGE indicates how many struct pages are used to store > extra metadata for a HugeTLB page. So we need to make sure the order > of a HugeTLB page should be bigger than or equal to order_base_2(__NR_USED_SUBPAGE). > So It is not related to HVO. I don't think the changes make sense. I did think about that but order_base_2(__NR_USED_SUBPAGE) actually turns out to be just 2 as __NR_USED_SUBPAGE is 3. Would not HugeTLB size be always greater than four base pages in reality, thus making this BUG_ON() check just redundant ? > > Thanks. > >> +#endif >> h = &hstates[hugetlb_max_hstate++]; >> __mutex_init(&h->resize_lock, "resize mutex", &h->resize_key); >> h->order = order; >> -- >> 2.30.2 >> >
