linux-kernel - Re: [PATCH v4 4/7] hugetlb: pass *next_nid_to_alloc directly to for_each_node_mask_to

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Date: Mon, 22 Jan 2024 17:50:26 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Gang Li <gang.li@...ux.dev>
Cc: David Hildenbrand <david@...hat.com>,
 David Rientjes <rientjes@...gle.com>,
 Mike Kravetz <mike.kravetz@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Tim Chen <tim.c.chen@...ux.intel.com>,
 Linux-MM <linux-mm@...ck.org>,
 LKML <linux-kernel@...r.kernel.org>,
 ligang.bdlg@...edance.com
Subject: Re: [PATCH v4 4/7] hugetlb: pass *next_nid_to_alloc directly to
 for_each_node_mask_to_alloc



> On Jan 22, 2024, at 17:14, Gang Li <gang.li@...ux.dev> wrote:
> 
> On 2024/1/22 14:16, Muchun Song wrote:
>> On 2024/1/18 20:39, Gang Li wrote:
>>>   static struct folio *alloc_pool_huge_folio(struct hstate *h,
>>>                       nodemask_t *nodes_allowed,
>>> -                    nodemask_t *node_alloc_noretry)
>>> +                    nodemask_t *node_alloc_noretry,
>>> +                    int *next_node)
>>>   {
>>>       gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
>>>       int nr_nodes, node;
>>> -    for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
>>> +    for_each_node_mask_to_alloc(next_node, nr_nodes, node, nodes_allowed) {
>> A small question here, why not pass h->next_nid_to_alloc to
>> for_each_node_mask_to_alloc()? What's the purpose of the third
>> parameter of alloc_pool_huge_folio()?
>> Thanks.
> 
> In hugetlb_alloc_node->alloc_pool_huge_folio, hugetlb is initialized in
> parallel at boot time, then it needs each thread to have its own
> next_nid, and can't use the global h->next_nid_to_alloc. so an extra parameter is added.

Yes. When I read your patch 6, I realized this.

> 
> And h->next_nid_to_alloc in set_max_huge_pages->alloc_pool_huge_folio
> can not be removed. Because if the user calls set_max_huge_pages
> frequently and only adds 1 page at a time, that would result in each
> request being made on the same node if local variables are used.