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Date: Thu, 14 Oct 2021 10:23:42 +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 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. > We should be able to catch this in hugetlb_cma_reserve. For the example > above, I think we should flag this as an error and not reserve any CMA. Sure, as I said above, it will not allocate CMA for the non-online nodes though these invalid nodes can be specified in the command line. But I can add a warning to catch the invalid nodes setting in hugetlb_cma_reserve(). >> + >> + s += count + 1; >> + tmp = memparse(s, &s); >> + hugetlb_cma_size_in_node[nid] = tmp; >> + hugetlb_cma_size += tmp; >> + >> + /* >> + * Skip the separator if have one, otherwise >> + * break the parsing. >> + */ >> + if (*s == ',') >> + s++; >> + else >> + break; >> + } else { >> + hugetlb_cma_size = memparse(p, &p); >> + break; >> + } >> + } >> + >> return 0; >> } >> >> @@ -6754,6 +6793,7 @@ static int __init cmdline_parse_hugetlb_cma(char *p) >> void __init hugetlb_cma_reserve(int order) >> { >> unsigned long size, reserved, per_node; >> + bool node_specific_cma_alloc = false; >> int nid; >> >> cma_reserve_called = true; >> @@ -6767,20 +6807,37 @@ void __init hugetlb_cma_reserve(int order) >> return; >> } > > Earlier in hugetlb_cma_reserve (not in the context here), there is this > code: > > if (hugetlb_cma_size < (PAGE_SIZE << order)) { > pr_warn("hugetlb_cma: cma area should be at least %lu MiB\n", > (PAGE_SIZE << order) / SZ_1M); > hugetlb_cma_size = 0; > return; > } > > That causes an early exit if hugetlb_cma_size is too small for a > gigantic page. > > On my 2 node x86 system with 1G gigantic pages, I can specify > 'hugetlb_cma=0:512M,1:512M'. This does not trigger the above early exit > because total hugetlb_cma_size is 1G. It does end up reserving 1G on > node 0 and nothing on node 1. I do not believe this is by design. We > should validate the specified per-node sizes as well. Sure. Will do in next version. Thanks for your comments.
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