Re: [PATCH] hugetlb: Support node specified when using cma for gigantic hugepages

[Mike Kravetz]

On 10/13/21 7:23 PM, Baolin Wang wrote:
> 
> 
> On 2021/10/14 6:06, Mike Kravetz wrote:
>> On 10/9/21 10:24 PM, Baolin Wang wrote:
>>> Now the size of CMA area for gigantic hugepages runtime allocation is
>>> balanced for all online nodes, but we also want to specify the size of
>>> CMA per-node, or only one node in some cases, which are similar with
>>> commit 86acc55c3d32 ("hugetlbfs: extend the definition of hugepages
>>> parameter to support node allocation")[1].
>>>
>>> Thus this patch adds node format for 'hugetlb_cma' parameter to support
>>> specifying the size of CMA per-node. An example is as follows:
>>>
>>> hugetlb_cma=0:5G,2:5G
>>>
>>> which means allocating 5G size of CMA area on node 0 and node 2
>>> respectively.
>>>
>>> [1]
>>> https://lkml.kernel.org/r/20211005054729.86457-1-yaozhenguo1@xxxxxxxxx
>>>
>>> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>>> ---
>>>   Documentation/admin-guide/kernel-parameters.txt |  6 +-
>>>   mm/hugetlb.c                                    | 79 +++++++++++++++++++++----
>>>   2 files changed, 73 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>> index 3ad8e9d0..a147faa5 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -1587,8 +1587,10 @@
>>>               registers.  Default set by CONFIG_HPET_MMAP_DEFAULT.
>>>         hugetlb_cma=    [HW,CMA] The size of a CMA area used for allocation
>>> -            of gigantic hugepages.
>>> -            Format: nn[KMGTPE]
>>> +            of gigantic hugepages. Or using node format, the size
>>> +            of a CMA area per node can be specified.
>>> +            Format: nn[KMGTPE] or (node format)
>>> +                <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
>>>                 Reserve a CMA area of given size and allocate gigantic
>>>               hugepages using the CMA allocator. If enabled, the
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 6d2f4c2..8b4e409 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -50,6 +50,7 @@
>>>     #ifdef CONFIG_CMA
>>>   static struct cma *hugetlb_cma[MAX_NUMNODES];
>>> +static unsigned long hugetlb_cma_size_in_node[MAX_NUMNODES] __initdata;
>>>   static bool hugetlb_cma_page(struct page *page, unsigned int order)
>>>   {
>>>       return cma_pages_valid(hugetlb_cma[page_to_nid(page)], page,
>>> @@ -62,6 +63,7 @@ static bool hugetlb_cma_page(struct page *page, unsigned int order)
>>>   }
>>>   #endif
>>>   static unsigned long hugetlb_cma_size __initdata;
>>> +static nodemask_t hugetlb_cma_nodes_allowed = NODE_MASK_NONE;
>>>     /*
>>>    * Minimum page order among possible hugepage sizes, set to a proper value
>>> @@ -3497,9 +3499,15 @@ static ssize_t __nr_hugepages_store_common(bool obey_mempolicy,
>>>         if (nid == NUMA_NO_NODE) {
>>>           /*
>>> +         * If we've specified the size of CMA area per node,
>>> +         * should use it firstly.
>>> +         */
>>> +        if (hstate_is_gigantic(h) && !nodes_empty(hugetlb_cma_nodes_allowed))
>>> +            n_mask = &hugetlb_cma_nodes_allowed;
>>> +        /*
>>
>> IIUC, this changes the behavior for 'balanced' gigantic huge page pool
>> allocations if per-node hugetlb_cma is specified.  It will now only
>> attempt to allocate gigantic pages on nodes where CMA was reserved.
>> Even if we run out of space on the node, it will not go to other nodes
>> as before.  Is that correct?
> 
> Right.
> 
>>
>> I do not believe we want this change in behavior.  IMO, if the user is
>> doing node specific CMA reservations, then the user should use the node
>> specific sysfs file for pool allocations on that node.
> 
> Sounds more reasonable, will move 'hugetlb_cma_nodes_allowed' to the node specific allocation.
> 
>>>            * global hstate attribute
>>>            */
>>> -        if (!(obey_mempolicy &&
>>> +        else if (!(obey_mempolicy &&
>>>                   init_nodemask_of_mempolicy(&nodes_allowed)))
>>>               n_mask = &node_states[N_MEMORY];
>>>           else
>>> @@ -6745,7 +6753,38 @@ void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
>>>     static int __init cmdline_parse_hugetlb_cma(char *p)
>>>   {
>>> -    hugetlb_cma_size = memparse(p, &p);
>>> +    int nid, count = 0;
>>> +    unsigned long tmp;
>>> +    char *s = p;
>>> +
>>> +    while (*s) {
>>> +        if (sscanf(s, "%lu%n", &tmp, &count) != 1)
>>> +            break;
>>> +
>>> +        if (s[count] == ':') {
>>> +            nid = tmp;
>>> +            if (nid < 0 || nid >= MAX_NUMNODES)
>>> +                break;
>>
>> nid can only be compared to MAX_NUMNODES because this an early param
>> before numa is setup and we do not know exactly how many nodes there
>> are.  Is this correct?
> 
> Yes.
> 
>>
>> Suppose one specifies an invaid node.  For example, on my 2 node system
>> I use the option 'hugetlb_cma=2:2G'.  This is not flagged as an error
>> during processing and 1G CMA is reserved on node 0 and 1G is reserved
>> on node 1.  Is that by design, or just chance?
> 
> Actually we won't allocate any CMA area in this case, since in hugetlb_cma_reserve(), we will only iterate the online nodes to try to allocate CMA area, and node 2 is not in the range of online nodes in this case.
> 

But, since it can not do node specifric allocations it falls through to
the all nodes case?  Here is what I see:

# numactl -H
available: 2 nodes (0-1)
node 0 cpus: 0 1
node 0 size: 8053 MB
node 0 free: 6543 MB
node 1 cpus: 2 3
node 1 size: 8150 MB
node 1 free: 4851 MB
node distances:
node   0   1
  0:  10  20
  1:  20  10

# reboot

# dmesg | grep -i huge
[    0.000000] Command line: BOOT_IMAGE=/vmlinuz-5.15.0-rc4-mm1+ root=/dev/mapper/fedora_new--host-root ro rd.lvm.lv=fedora_new-host/root rd.lvm.lv=fedora_new-host/swap console=tty0 console=ttyS0,115200 audit=0 transparent_hugepage=always hugetlb_free_vmemmap=on hugetlb_cma=2:2G
[    0.008345] hugetlb_cma: reserve 2048 MiB, up to 1024 MiB per node
[    0.008349] hugetlb_cma: reserved 1024 MiB on node 0
[    0.008352] hugetlb_cma: reserved 1024 MiB on node 1
[    0.053682] Kernel command line: BOOT_IMAGE=/vmlinuz-5.15.0-rc4-mm1+ root=/dev/mapper/fedora_new--host-root ro rd.lvm.lv=fedora_new-host/root rd.lvm.lv=fedora_new-host/swap console=tty0 console=ttyS0,115200 audit=0 transparent_hugepage=always hugetlb_free_vmemmap=on hugetlb_cma=2:2G
[    0.401648] HugeTLB: can free 4094 vmemmap pages for hugepages-1048576kB
[    0.413681] HugeTLB: can free 6 vmemmap pages for hugepages-2048kB
[    0.414590] HugeTLB registered 1.00 GiB page size, pre-allocated 0 pages
[    0.415653] HugeTLB registered 2.00 MiB page size, pre-allocated 0 pages

-- 
Mike Kravetz