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

[Chen Wandun <chenwandun@huawei.com>]

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,
Wandun

> 
>> -                       nr = alloc_pages_bulk_array_node(gfp, nid,
>> -                               nr_pages_request, pages + nr_allocated);
>> -
>> +                       if (nid == NUMA_NO_NODE) {
>> +                               for (i = 0; i < nr_pages_request; i++) {
>> +                                       page = alloc_page(gfp);
>> +                                       if (page)
>> +                                               pages[nr_allocated + i] = page;
>> +                                       else {
>> +                                               nr = i;
>> +                                               break;
>> +                                       }
>> +                               }
>> +                               if (i >= nr_pages_request)
>> +                                       nr = nr_pages_request;
>> +                       } else {
>> +                               nr = alloc_pages_bulk_array_node(gfp, nid,
>> +                                                       nr_pages_request,
>> +                                                       pages + nr_allocated);
>> +                       }
>>                          nr_allocated += nr;
>>                          cond_resched();
>>
>> @@ -2863,11 +2880,13 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> 
> Put the following line under "else if (order)"
> 
>>                  gfp |= __GFP_COMP;
>>
>>          /* High-order pages or fallback path if "bulk" fails. */
>> -       while (nr_allocated < nr_pages) {
> 
> Keep the following declarations inside the while loop.
> 
>> -               struct page *page;
>> -               int i;
>>
>> -               page = alloc_pages_node(nid, gfp, order);
>> +       page = NULL;
>> +       while (nr_allocated < nr_pages) {
>> +               if (nid == NUMA_NO_NODE)
>> +                       page = alloc_pages(gfp, order);
>> +               else
>> +                       page = alloc_pages_node(nid, gfp, order);
>>                  if (unlikely(!page))
>>                          break;
>>
>> --
>> 2.25.1
>>
> . 
>