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Date:   Fri, 15 Oct 2021 10:31:17 +0800
From:   Chen Wandun <chenwandun@...wei.com>
To:     Nicholas Piggin <npiggin@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Eric Dumazet <edumazet@...gle.com>, <guohanjun@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH] mm/vmalloc: fix numa spreading for large hash tables



在 2021/10/15 9:34, Nicholas Piggin 写道:
> Excerpts from Chen Wandun's message of October 14, 2021 6:59 pm:
>>
>>
>> 在 2021/10/14 5:46, Shakeel Butt 写道:
>>> On Tue, Sep 28, 2021 at 5:03 AM Chen Wandun <chenwandun@...wei.com> 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@...gle.com>
>>>> Signed-off-by: Chen Wandun <chenwandun@...wei.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) {
>>>
>>> Can you please replace the above with if (!order && nid != NUMA_NO_NODE)?
>>>
>>>>                   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);
>>>>
>>>
>>> Undo the following change in this if block.
>>
>> Yes, It seem like more simpler as you suggested, But it still have
>> performance regression, I plan to change the following to consider
>> both mempolcy and alloc_pages_bulk.
> 
> Thanks for finding and debugging this. These APIs are a maze of twisty
> little passages, all alike so I could be as confused as I was when I
> wrote that patch, but doesn't a minimal fix look something like this?

Yes, I sent a patch,it looks like as you show, besides it also
contains some performance optimization.

[PATCH] mm/vmalloc: introduce alloc_pages_bulk_array_mempolicy to 
accelerate memory allocation

Thanks,
Wandun

> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d77830ff604c..75ee9679f521 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2860,7 +2860,10 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>                  struct page *page;
>                  int i;
>   
> -               page = alloc_pages_node(nid, gfp, order);
> +               if (nid == NUMA_NO_NODE)
> +                       page = alloc_pages(gfp, order);
> +               else
> +                       page = alloc_pages_node(nid, gfp, order);
>                  if (unlikely(!page))
>                          break;
>   
> 
> Thanks,
> Nick
> .
> 

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