linux-kernel - Re: [PATCH v4] hugetlbfs: Extend the definition of hugepages parameter to support node allocation

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Message-ID: <c55f0be5-f68d-1a33-a9e4-5890a2887a15@oracle.com>
Date:   Wed, 15 Sep 2021 15:03:30 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     zhenguo yao <yaozhenguo1@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     corbet@....net, yaozhenguo@...com,
        Matthew Wilcox <willy@...radead.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH v4] hugetlbfs: Extend the definition of hugepages
 parameter to support node allocation

On 9/15/21 6:11 AM, zhenguo yao wrote:
> Andrew Morton <akpm@...ux-foundation.org> 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@...il.com> 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.
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.
-- 
Mike Kravetz