Re: [PATCH v2 1/2] mm/vmalloc: fix numa spreading for large hash tables

[Uladzislau Rezki <urezki@gmail.com>]

> 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 | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d77830ff604c..87552a4018aa 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2816,6 +2816,8 @@ 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
> @@ -2823,7 +2825,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>          * to fails, fallback to a single page allocator that is
>          * more permissive.
>          */
> -       if (!order) {
> +       if (!order && nid != NUMA_NO_NODE) {
>                 while (nr_allocated < nr_pages) {
>                         unsigned int nr, nr_pages_request;
>
> @@ -2848,7 +2850,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>                         if (nr != nr_pages_request)
>                                 break;
>                 }
> -       } else
> +       } else if (order)
>                 /*
>                  * Compound pages required for remap_vmalloc_page if
>                  * high-order pages.
> @@ -2856,11 +2858,13 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>                 gfp |= __GFP_COMP;
>
>         /* High-order pages or fallback path if "bulk" fails. */
> -       while (nr_allocated < nr_pages) {
> -               struct page *page;
> -               int i;
>
> -               page = alloc_pages_node(nid, gfp, order);
> +       page = NULL;
>
Why do you need to set page to NULL here?

-- 
Vlad Rezki