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SubjectRe: [PATCH] mm/vmalloc: fix numa spreading for large hash tables
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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@huawei.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@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) {
>>>
>>> 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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