CC some vmalloc folks. What happened was vmalloc huge pages was turned on for x86 with the rest of the kernel unprepared and problems have popped up. We are discussing a possible new config and vmap flag such that for some arch's, huge pages would only be used for certain allocations such as BPF's. Thread: https://lore.kernel.org/lkml/6080EC28-E3FE-4B00-B94A-ED7EBA1F55ED@xxxxxx/ On Tue, 2022-03-29 at 08:23 +0000, Song Liu wrote: > > On Mar 28, 2022, at 5:18 PM, Edgecombe, Rick P < > > rick.p.edgecombe@xxxxxxxxx> wrote: > > > > On Mon, 2022-03-28 at 23:27 +0000, Song Liu wrote: > > > I like this direction. But I am afraid this is not enough. Using > > > VM_NO_HUGE_VMAP in module_alloc() will make sure we don't > > > allocate > > > huge pages for modules. But other users of > > > __vmalloc_node_range(), > > > such as vzalloc in Paul's report, may still hit the issue. > > > > > > Maybe we need another flag VM_FORCE_HUGE_VMAP that bypasses > > > vmap_allow_huge check. Something like the diff below. > > > > > > Would this work? > > > > Yea, that looks like a safer direction. It's too bad we can't have > > automatic large pages, but it doesn't seem ready to just turn on > > for > > the whole x86 kernel. > > > > I'm not sure about this implementation though. It would let large > > pages > > get enabled without HAVE_ARCH_HUGE_VMALLOC and also despite the > > disable > > kernel parameter. > > > > Apparently some architectures can handle large pages automatically > > and > > it has benefits for them, so maybe vmalloc should support both > > behaviors based on config. Like there should a > > ARCH_HUGE_VMALLOC_REQUIRE_FLAG config. If configured it requires > > VM_HUGE_VMAP (or some name). I don't think FORCE fits, because the > > current logic would not always give huge pages. > > > > But yea, seems risky to leave it on generally, even if you could > > fix > > Paul's specific issue. > > > > > How about something like the following? (I still need to fix > something, but > would like some feedbacks on the API). > > Thanks, > Song > > > diff --git a/arch/Kconfig b/arch/Kconfig > index 84bc1de02720..defef50ff527 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -858,6 +858,15 @@ config HAVE_ARCH_HUGE_VMALLOC > depends on HAVE_ARCH_HUGE_VMAP > bool > > +# > +# HAVE_ARCH_HUGE_VMALLOC_FLAG allows users of __vmalloc_node_range > to allocate > +# huge page without HAVE_ARCH_HUGE_VMALLOC. To allocate huge pages,, > the user > +# need to call __vmalloc_node_range with VM_PREFER_HUGE_VMAP. > +# > +config HAVE_ARCH_HUGE_VMALLOC_FLAG > + depends on HAVE_ARCH_HUGE_VMAP > + bool > + > config ARCH_WANT_HUGE_PMD_SHARE > bool > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 7340d9f01b62..e64f00415575 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -161,7 +161,7 @@ config X86 > select HAVE_ALIGNED_STRUCT_PAGE if SLUB > select HAVE_ARCH_AUDITSYSCALL > select HAVE_ARCH_HUGE_VMAP if X86_64 || X86_PAE > - select HAVE_ARCH_HUGE_VMALLOC if X86_64 > + select HAVE_ARCH_HUGE_VMALLOC_FLAG if X86_64 > select HAVE_ARCH_JUMP_LABEL > select HAVE_ARCH_JUMP_LABEL_RELATIVE > select HAVE_ARCH_KASAN if X86_64 > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h > index 3b1df7da402d..98f8a93fcfd4 100644 > --- a/include/linux/vmalloc.h > +++ b/include/linux/vmalloc.h > @@ -35,6 +35,11 @@ struct notifier_block; /* in > notifier.h */ > #define VM_DEFER_KMEMLEAK 0 > #endif > > +#ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG > +#define VM_PREFER_HUGE_VMAP 0x00001000 /* prefer PMD_SIZE > mapping (bypass vmap_allow_huge check) */ I don't think we should tie this to vmap_allow_huge by definition. Also, what it does is try 2MB pages for allocations larger than 2MB. For smaller allocations it doesn't try or "prefer" them. > +#else > +#define VM_PREFER_HUGE_VMAP 0 > +#endif > /* bits [20..32] reserved for arch specific ioremap internals */ > > /* > @@ -51,7 +56,7 @@ struct vm_struct { > unsigned long size; > unsigned long flags; > struct page **pages; > -#ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC > +#if (defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC) || > defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG)) > unsigned int page_order; > #endif > unsigned int nr_pages; > @@ -225,7 +230,7 @@ static inline bool is_vm_area_hugepages(const > void *addr) > * prevents that. This only indicates the size of the physical > page > * allocated in the vmalloc layer. > */ > -#ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC > +#if (defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC) || > defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG)) > return find_vm_area(addr)->page_order > 0; > #else > return false; > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c > index 13e9dbeeedf3..fc9dae095079 100644 > --- a/kernel/bpf/core.c > +++ b/kernel/bpf/core.c > @@ -851,13 +851,28 @@ static LIST_HEAD(pack_list); > #define BPF_HPAGE_MASK PAGE_MASK > #endif > > +static void *bpf_prog_pack_vmalloc(unsigned long size) > +{ > +#if defined(MODULES_VADDR) > + unsigned long start = MODULES_VADDR; > + unsigned long end = MODULES_END; > +#else > + unsigned long start = VMALLOC_START; > + unsigned long end = VMALLOC_END; > +#endif > + > + return __vmalloc_node_range(size, PAGE_SIZE, start, end, > GFP_KERNEL, PAGE_KERNEL, > + VM_DEFER_KMEMLEAK | > VM_PREFER_HUGE_VMAP, > + NUMA_NO_NODE, > __builtin_return_address(0)); > +} > + > static size_t select_bpf_prog_pack_size(void) > { > size_t size; > void *ptr; > > size = BPF_HPAGE_SIZE * num_online_nodes(); > - ptr = module_alloc(size); > + ptr = bpf_prog_pack_vmalloc(size); > > /* Test whether we can get huge pages. If not just use > PAGE_SIZE > * packs. > @@ -881,7 +896,7 @@ static struct bpf_prog_pack *alloc_new_pack(void) > GFP_KERNEL); > if (!pack) > return NULL; > - pack->ptr = module_alloc(bpf_prog_pack_size); > + pack->ptr = bpf_prog_pack_vmalloc(bpf_prog_pack_size); > if (!pack->ptr) { > kfree(pack); > return NULL; > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index e163372d3967..9d3c1ab8bdf1 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -2261,7 +2261,7 @@ static inline unsigned int > vm_area_page_order(struct vm_struct *vm) > > static inline void set_vm_area_page_order(struct vm_struct *vm, > unsigned int order) > { > -#ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC > +#if (defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC) || > defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG)) > vm->page_order = order; > #else > BUG_ON(order != 0); > @@ -3106,7 +3106,8 @@ void *__vmalloc_node_range(unsigned long size, > unsigned long align, > return NULL; > } > > - if (vmap_allow_huge && !(vm_flags & VM_NO_HUGE_VMAP)) { > + if ((vmap_allow_huge && !(vm_flags & VM_NO_HUGE_VMAP)) || > + (IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG) && > (vm_flags & VM_PREFER_HUGE_VMAP))) { vmap_allow_huge is how the kernel parameter that can disable vmalloc huge pages works. I don't think we should separate it. Disabling vmalloc huge pages should still disable this alternate mode. > unsigned long size_per_node; > > /*
