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Date: Tue, 2 Jan 2024 17:32:15 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Gang Li <gang.li@linux.dev>
cc: David Hildenbrand <david@redhat.com>, 
    Mike Kravetz <mike.kravetz@oracle.com>, 
    Muchun Song <muchun.song@linux.dev>, 
    Andrew Morton <akpm@linux-foundation.org>, 
    Tim Chen <tim.c.chen@linux.intel.com>, linux-mm@kvack.org, 
    linux-kernel@vger.kernel.org, ligang.bdlg@bytedance.com
Subject: Re: [PATCH v3 4/7] hugetlb: pass *next_nid_to_alloc directly to
 for_each_node_mask_to_alloc
In-Reply-To: <20240102131249.76622-5-gang.li@linux.dev>
Message-ID: <19b08bb8-1fbd-557b-2684-5c29c5c783e6@google.com>
References: <20240102131249.76622-1-gang.li@linux.dev> <20240102131249.76622-5-gang.li@linux.dev>
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On Tue, 2 Jan 2024, Gang Li wrote:

> The parallelization of hugetlb allocation leads to errors when sharing
> h->next_nid_to_alloc across different threads. To address this, it's
> necessary to assign a separate next_nid_to_alloc for each thread.
> 
> Consequently, the hstate_next_node_to_alloc and for_each_node_mask_to_alloc
> have been modified to directly accept a *next_nid_to_alloc parameter,
> ensuring thread-specific allocation and avoiding concurrent access issues.
> 
> Signed-off-by: Gang Li <gang.li@linux.dev>
> ---
> This patch seems not elegant, but I can't come up with anything better.
> Any suggestions will be highly appreciated!

Same error as v2:

mm/hugetlb.c:3315:53: warning: variable 'node' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
        for_each_node_mask_to_alloc(&h->next_nid_to_alloc, nr_nodes, node, &node_states[N_MEMORY]) {
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/hugetlb.c:1501:3: note: expanded from macro 'for_each_node_mask_to_alloc'
                nr_nodes > 0 &&                                         \
                ^~~~~~~~~~~~
mm/hugetlb.c:3342:38: note: uninitialized use occurs here
        list_add(&m->list, &huge_boot_pages[node]);
                                            ^~~~
mm/hugetlb.c:3315:53: note: remove the '&&' if its condition is always true
        for_each_node_mask_to_alloc(&h->next_nid_to_alloc, nr_nodes, node, &node_states[N_MEMORY]) {
                                                           ^
mm/hugetlb.c:3310:7: warning: variable 'node' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
                if (!m)
                    ^~
mm/hugetlb.c:3342:38: note: uninitialized use occurs here
        list_add(&m->list, &huge_boot_pages[node]);
                                            ^~~~
mm/hugetlb.c:3310:3: note: remove the 'if' if its condition is always true
                if (!m)
                ^~~~~~~
mm/hugetlb.c:3304:20: note: initialize the variable 'node' to silence this warning
        int nr_nodes, node;
                          ^
                           = 0
2 warnings generated.

> ---
>  mm/hugetlb.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 92448e747991d..a71bc1622b53b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1464,15 +1464,15 @@ static int get_valid_node_allowed(int nid, nodemask_t *nodes_allowed)
>   * next node from which to allocate, handling wrap at end of node
>   * mask.
>   */
> -static int hstate_next_node_to_alloc(struct hstate *h,
> +static int hstate_next_node_to_alloc(int *next_nid_to_alloc,
>  					nodemask_t *nodes_allowed)
>  {
>  	int nid;
>  
>  	VM_BUG_ON(!nodes_allowed);
>  
> -	nid = get_valid_node_allowed(h->next_nid_to_alloc, nodes_allowed);
> -	h->next_nid_to_alloc = next_node_allowed(nid, nodes_allowed);
> +	nid = get_valid_node_allowed(*next_nid_to_alloc, nodes_allowed);
> +	*next_nid_to_alloc = next_node_allowed(nid, nodes_allowed);
>  
>  	return nid;
>  }
> @@ -1495,10 +1495,10 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
>  	return nid;
>  }
>  
> -#define for_each_node_mask_to_alloc(hs, nr_nodes, node, mask)		\
> +#define for_each_node_mask_to_alloc(next_nid_to_alloc, nr_nodes, node, mask)		\
>  	for (nr_nodes = nodes_weight(*mask);				\
>  		nr_nodes > 0 &&						\
> -		((node = hstate_next_node_to_alloc(hs, mask)) || 1);	\
> +		((node = hstate_next_node_to_alloc(next_nid_to_alloc, mask)) || 1);	\
>  		nr_nodes--)
>  
>  #define for_each_node_mask_to_free(hs, nr_nodes, node, mask)		\
> @@ -2350,12 +2350,13 @@ static void prep_and_add_allocated_folios(struct hstate *h,
>   */
>  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_nid_to_alloc)
>  {
>  	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_nid_to_alloc, nr_nodes, node, nodes_allowed) {
>  		struct folio *folio;
>  
>  		folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, node,
> @@ -3310,7 +3311,7 @@ int __alloc_bootmem_huge_page(struct hstate *h, int nid)
>  		goto found;
>  	}
>  	/* allocate from next node when distributing huge pages */
> -	for_each_node_mask_to_alloc(h, nr_nodes, node, &node_states[N_MEMORY]) {
> +	for_each_node_mask_to_alloc(&h->next_nid_to_alloc, nr_nodes, node, &node_states[N_MEMORY]) {
>  		m = memblock_alloc_try_nid_raw(
>  				huge_page_size(h), huge_page_size(h),
>  				0, MEMBLOCK_ALLOC_ACCESSIBLE, node);
> @@ -3684,7 +3685,7 @@ static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
>  	VM_BUG_ON(delta != -1 && delta != 1);
>  
>  	if (delta < 0) {
> -		for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
> +		for_each_node_mask_to_alloc(&h->next_nid_to_alloc, nr_nodes, node, nodes_allowed) {
>  			if (h->surplus_huge_pages_node[node])
>  				goto found;
>  		}
> @@ -3799,7 +3800,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>  		cond_resched();
>  
>  		folio = alloc_pool_huge_folio(h, nodes_allowed,
> -						node_alloc_noretry);
> +						node_alloc_noretry,
> +						&h->next_nid_to_alloc);
>  		if (!folio) {
>  			prep_and_add_allocated_folios(h, &page_list);
>  			spin_lock_irq(&hugetlb_lock);
> -- 
> 2.20.1
> 
>