Re: [PATCH] mm/vmalloc: fix numa spreading for large hash tables

[Uladzislau Rezki <urezki@gmail.com>]

On Tue, Sep 28, 2021 at 08:10:40PM +0800, Chen Wandun wrote:
> Eric Dumazet reported a strange numa spreading info in [1], and found
> commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings") introduced
> this issue [2].
> 
> Dig into the difference before and after this patch, page allocation has
> some difference:
> 
> before:
> alloc_large_system_hash
>     __vmalloc
>         __vmalloc_node(..., NUMA_NO_NODE, ...)
>             __vmalloc_node_range
>                 __vmalloc_area_node
>                     alloc_page /* because NUMA_NO_NODE, so choose alloc_page branch */
>                         alloc_pages_current
>                             alloc_page_interleave /* can be proved by print policy mode */
> 
> after:
> alloc_large_system_hash
>     __vmalloc
>         __vmalloc_node(..., NUMA_NO_NODE, ...)
>             __vmalloc_node_range
>                 __vmalloc_area_node
>                     alloc_pages_node /* choose nid by nuam_mem_id() */
>                         __alloc_pages_node(nid, ....)
> 
> So after commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings"),
> it will allocate memory in current node instead of interleaving allocate
> memory.
> 
> [1]
> https://lore.kernel.org/linux-mm/CANn89iL6AAyWhfxdHO+jaT075iOa3XcYn9k6JJc7JR2XYn6k_Q@mail.gmail.com/
> 
> [2]
> https://lore.kernel.org/linux-mm/CANn89iLofTR=AK-QOZY87RdUZENCZUT4O6a0hvhu3_EwRMerOg@mail.gmail.com/
> 
> Fixes: 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings")
> Reported-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Chen Wandun <chenwandun@huawei.com>
> ---
>  mm/vmalloc.c | 33 ++++++++++++++++++++++++++-------
>  1 file changed, 26 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index f884706c5280..48e717626e94 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2823,6 +2823,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  		unsigned int order, unsigned int nr_pages, struct page **pages)
>  {
>  	unsigned int nr_allocated = 0;
> +	struct page *page;
> +	int i;
>  
>  	/*
>  	 * For order-0 pages we make use of bulk allocator, if
> @@ -2833,6 +2835,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  	if (!order) {
>  		while (nr_allocated < nr_pages) {
>  			unsigned int nr, nr_pages_request;
> +			page = NULL;
>  
>  			/*
>  			 * A maximum allowed request is hard-coded and is 100
> @@ -2842,9 +2845,23 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  			 */
>  			nr_pages_request = min(100U, nr_pages - nr_allocated);
>  
> -			nr = alloc_pages_bulk_array_node(gfp, nid,
> -				nr_pages_request, pages + nr_allocated);
> -
> +			if (nid == NUMA_NO_NODE) {
>
<snip>
void *vmalloc(unsigned long size)
{
	return __vmalloc_node(size, 1, GFP_KERNEL, NUMA_NO_NODE,
		__builtin_return_address(0));
}
EXPORT_SYMBOL(vmalloc);
<snip>

vmalloc() uses NUMA_NO_NODE, so all vmalloc calls will be reverted to a single
page allocator for NUMA and non-NUMA systems. Is it intentional to bypass the
optimized bulk allocator for non-NUMA systems? 

Thanks!

--
Vlad Rezki