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Date: Thu, 14 Oct 2021 10:39:25 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Mike Kravetz <mike.kravetz@...cle.com>, akpm@...ux-foundation.org
Cc: mhocko@...nel.org, guro@...com, corbet@....net,
yaozhenguo1@...il.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] hugetlb: Support node specified when using cma for
gigantic hugepages
在 2021/10/14 10:30, Mike Kravetz 写道:
> 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@gmail.com
>>>>
>>>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>>>> ---
>>>> 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
Oh, I see. I only validate the online nodes to check if we've specified
the size of CMA, so in this case, it will fall back to the original
balanced policy. As you said, I should catch the invalid nodes in
hugetlb_cma_reserve() to avoid this isse. Thanks for pointing out the issue.
+ for_each_node_state(nid, N_ONLINE) {
+ if (hugetlb_cma_size_in_node[nid] > 0) {
+ node_specific_cma_alloc = true;
+ break;
+ }
+ }
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