| Message ID | 20210608180618.477766-2-imbrenda@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: export __vmalloc_node_range and use it | expand |
On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote: > The recent patches to add support for hugepage vmalloc mappings added a > flag for __vmalloc_node_range to allow to request small pages. > This flag is not accessible when calling vmalloc, the only option is to > call directly __vmalloc_node_range, which is not exported. > > This means that a module can't vmalloc memory with small pages. > > Case in point: KVM on s390x needs to vmalloc a large area, and it needs > to be mapped with small pages, because of a hardware limitation. > > This patch exports __vmalloc_node_range so it can be used in modules > too. No. I spent a lot of effort to mak sure such a low-level API is not exported.
On Wed, 9 Jun 2021 16:59:17 +0100 Christoph Hellwig <hch@infradead.org> wrote: > On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote: > > The recent patches to add support for hugepage vmalloc mappings > > added a flag for __vmalloc_node_range to allow to request small > > pages. This flag is not accessible when calling vmalloc, the only > > option is to call directly __vmalloc_node_range, which is not > > exported. > > > > This means that a module can't vmalloc memory with small pages. > > > > Case in point: KVM on s390x needs to vmalloc a large area, and it > > needs to be mapped with small pages, because of a hardware > > limitation. > > > > This patch exports __vmalloc_node_range so it can be used in modules > > too. > > No. I spent a lot of effort to mak sure such a low-level API is > not exported. ok, but then how can we vmalloc memory with small pages from KVM?
On Wed, Jun 09, 2021 at 06:28:09PM +0200, Claudio Imbrenda wrote: > On Wed, 9 Jun 2021 16:59:17 +0100 > Christoph Hellwig <hch@infradead.org> wrote: > > > On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote: > > > The recent patches to add support for hugepage vmalloc mappings > > > added a flag for __vmalloc_node_range to allow to request small > > > pages. This flag is not accessible when calling vmalloc, the only > > > option is to call directly __vmalloc_node_range, which is not > > > exported. > > > > > > This means that a module can't vmalloc memory with small pages. > > > > > > Case in point: KVM on s390x needs to vmalloc a large area, and it > > > needs to be mapped with small pages, because of a hardware > > > limitation. > > > > > > This patch exports __vmalloc_node_range so it can be used in modules > > > too. > > > > No. I spent a lot of effort to mak sure such a low-level API is > > not exported. > > ok, but then how can we vmalloc memory with small pages from KVM? Does the s390x support CONFIG_HAVE_ARCH_HUGE_VMALLOC what is arch specific? If not then small pages are used. Or am i missing something? I agree with Christoph that exporting a low level internals is not a good idea. -- Vlad Rezki
On 09.06.21 18:28, Claudio Imbrenda wrote: > On Wed, 9 Jun 2021 16:59:17 +0100 > Christoph Hellwig <hch@infradead.org> wrote: > >> On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote: >>> The recent patches to add support for hugepage vmalloc mappings >>> added a flag for __vmalloc_node_range to allow to request small >>> pages. This flag is not accessible when calling vmalloc, the only >>> option is to call directly __vmalloc_node_range, which is not >>> exported. >>> >>> This means that a module can't vmalloc memory with small pages. >>> >>> Case in point: KVM on s390x needs to vmalloc a large area, and it >>> needs to be mapped with small pages, because of a hardware >>> limitation. >>> >>> This patch exports __vmalloc_node_range so it can be used in modules >>> too. >> >> No. I spent a lot of effort to mak sure such a low-level API is >> not exported. > > ok, but then how can we vmalloc memory with small pages from KVM? An alternative would be to provide a vmalloc_no_huge function in generic code (similar to vmalloc_32) (or if preferred in s390 base architecture code) Something like void *vmalloc_no_huge(unsigned long size) { return __vmalloc_node_flags(size, NUMA_NO_NODE,VM_NO_HUGE_VMAP | GFP_KERNEL | __GFP_ZERO); } EXPORT_SYMBOL(vmalloc_no_huge); or a similar vzalloc variant.
On 09.06.21 18:49, Uladzislau Rezki wrote: > On Wed, Jun 09, 2021 at 06:28:09PM +0200, Claudio Imbrenda wrote: >> On Wed, 9 Jun 2021 16:59:17 +0100 >> Christoph Hellwig <hch@infradead.org> wrote: >> >>> On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote: >>>> The recent patches to add support for hugepage vmalloc mappings >>>> added a flag for __vmalloc_node_range to allow to request small >>>> pages. This flag is not accessible when calling vmalloc, the only >>>> option is to call directly __vmalloc_node_range, which is not >>>> exported. >>>> >>>> This means that a module can't vmalloc memory with small pages. >>>> >>>> Case in point: KVM on s390x needs to vmalloc a large area, and it >>>> needs to be mapped with small pages, because of a hardware >>>> limitation. >>>> >>>> This patch exports __vmalloc_node_range so it can be used in modules >>>> too. >>> >>> No. I spent a lot of effort to mak sure such a low-level API is >>> not exported. >> >> ok, but then how can we vmalloc memory with small pages from KVM? > Does the s390x support CONFIG_HAVE_ARCH_HUGE_VMALLOC what is arch > specific? Not yet, but we surely want that for almost everything on s390. Only this particular firmware interface does not handle large pages for donated memory. > > If not then small pages are used. Or am i missing something? > > I agree with Christoph that exporting a low level internals > is not a good idea.
On Wed, Jun 09, 2021 at 07:47:43PM +0200, Christian Borntraeger wrote: > An alternative would be to provide a vmalloc_no_huge function in generic > code (similar to vmalloc_32) (or if preferred in s390 base architecture code) > Something like > > void *vmalloc_no_huge(unsigned long size) > { > return __vmalloc_node_flags(size, NUMA_NO_NODE,VM_NO_HUGE_VMAP | > GFP_KERNEL | __GFP_ZERO); > } > EXPORT_SYMBOL(vmalloc_no_huge); > > or a similar vzalloc variant. Exactly. Given that this seems to be a weird pecularity of legacy s390 interfaces I'd only export it for 390 for now, although for documentation purposes I'd probably still keep it in vmalloc.c.
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index a13ac524f6ff..bd6fa160b31b 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2937,6 +2937,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, return NULL; } +EXPORT_SYMBOL_GPL(__vmalloc_node_range); /** * __vmalloc_node - allocate virtually contiguous memory
The recent patches to add support for hugepage vmalloc mappings added a flag for __vmalloc_node_range to allow to request small pages. This flag is not accessible when calling vmalloc, the only option is to call directly __vmalloc_node_range, which is not exported. This means that a module can't vmalloc memory with small pages. Case in point: KVM on s390x needs to vmalloc a large area, and it needs to be mapped with small pages, because of a hardware limitation. This patch exports __vmalloc_node_range so it can be used in modules too. Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Uladzislau Rezki (Sony) <urezki@gmail.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: David Rientjes <rientjes@google.com> --- mm/vmalloc.c | 1 + 1 file changed, 1 insertion(+)