Hi Mike,
On Wed, Sep 15, 2021 at 03:05:41PM -0700, Mike Kravetz wrote:
> Now, really CC'ing Mike, and sorry for misspelling your name
>
> On 9/15/21 3:03 PM, Mike Kravetz wrote:
> > On 9/15/21 6:11 AM, zhenguo yao wrote:
> >> Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> 于2021年9月15日周三 上午11:50写道：
> >>>
> >>> On Thu, 9 Sep 2021 22:16:55 +0800 yaozhenguo <yaozhenguo1@xxxxxxxxx> wrote:
> >>>
> >>>> We can specify the number of hugepages to allocate at boot. But the
> >>>> hugepages is balanced in all nodes at present. In some scenarios,
> >>>> we only need hugepages in one node. For example: DPDK needs hugepages
> >>>> which are in the same node as NIC. if DPDK needs four hugepages of 1G
> >>>> size in node1 and system has 16 numa nodes. We must reserve 64 hugepages
> >>>> in kernel cmdline. But, only four hugepages are used. The others should
> >>>> be free after boot. If the system memory is low(for example: 64G), it will
> >>>> be an impossible task. So, Extending hugepages parameter to support
> >>>> specifying hugepages at a specific node.
> >>>> For example add following parameter:
> >>>>
> >>>> hugepagesz=1G hugepages=0:1,1:3
> >>>>
> >>>> It will allocate 1 hugepage in node0 and 3 hugepages in node1.
> >>>>
> >>>> ...
> >>>>
> >>>> @@ -2842,10 +2843,75 @@ static void __init gather_bootmem_prealloc(void)
> >>>> }
> >>>> }
> >>>>
> >>>> +static void __init hugetlb_hstate_alloc_pages_onenode(struct hstate *h, int nid)
> >>>> +{
> >>>> + unsigned long i;
> >>>> + char buf[32];
> >>>> +
> >>>> + for (i = 0; i < h->max_huge_pages_node[nid]; ++i) {
> >>>> + if (hstate_is_gigantic(h)) {
> >>>> + struct huge_bootmem_page *m;
> >>>> + void *addr;
> >>>> +
> >>>> + addr = memblock_alloc_try_nid_raw(
> >>>> + huge_page_size(h), huge_page_size(h),
> >>>> + 0, MEMBLOCK_ALLOC_ACCESSIBLE, nid);
> >>>> + if (!addr)
> >>>> + break;
> >>>> + m = addr;
> >>>> + BUG_ON(!IS_ALIGNED(virt_to_phys(m), huge_page_size(h)));
> >>>
> >>> We try very hard to avoid adding BUG calls. Is there any way in which
> >>> this code can emit a WARNing then permit the kernel to keep operating?
> >>>
> >> Maybe we can rewrite it as below:
> >> if (WARN(!IS_ALIGNED(virt_to_phys(m),
> >> huge_page_size(h)),
> >> "HugeTLB: page addr:%p is not aligned\n", m))
> >> break;
> >> @Mike, Do you think it's OK?
> >
> > Sorry, I have not yet reviewed the latest version of this patch.
> > Quick thought on this question.
> >
> > The required alignment passed to memblock_alloc_try_nid_raw() is
> > huge_page_size(h). Therefore, we know the virtual address m is
> > huge_page_size(h) aligned. The BUG is just checking to make sure
> > the physical address associated with the virtual address is aligned
> > the same. I really do not see how this could not be the case.
> > In fact, the memblock allocator finds a physical address with the
> > required alignment and then returns phys_to_virt(alloc).
> > Someone please correct me if I am wrong. Otherwise, we can drop
> > the BUG.
I agree with your analysis and I also think the BUG() can be dropped
entirely as well as the BUG() in __alloc_bootmem_huge_page().
> > Adding Mike Rapport on Cc:
> >
> > This allocation code and the associated BUG was copied from
> > __alloc_bootmem_huge_page(). The BUG was added 12 years ago before
> > the memblock allocator existed and we were using the bootmem allocator.
> > If there is no need for a BUG in hugetlb_hstate_alloc_pages_onenode,
> > there is no need for one in __alloc_bootmem_huge_page.
Hmm, even bootmem had alignment guaranties so it seems to me that the BUG()
was over-protective even then.
--
Sincerely yours,
Mike.
