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Re: __GFP_REPEAT usage in fq_alloc_node

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On 01/06/2017 04:39 PM, Eric Dumazet wrote:
> On Fri, Jan 6, 2017 at 7:20 AM, Michal Hocko <mhocko@kernel.org> wrote:
>>
>> Hi Eric,
>> I am currently checking kmalloc with vmalloc fallback users and convert
>> them to a new kvmalloc helper [1]. While I am adding a support for
>> __GFP_REPEAT to kvmalloc [2] I was wondering what is the reason to use
>> __GFP_REPEAT in fq_alloc_node in the first place. c3bd85495aef
>> ("pkt_sched: fq: more robust memory allocation") doesn't mention
>> anything. Could you clarify this please?
>>
>> Thanks!
> 
> I guess this question applies to all __GFP_REPEAT usages in net/ ?
> 
> At the time, tests on the hardware I had in my labs showed that
> vmalloc() could deliver pages spread
> all over the memory and that was a small penalty (once memory is
> fragmented enough, not at boot time)

I wonder what's that cause of the penalty (when accessing the vmapped
area I suppose?) Is it higher risk of collisions cache misses within the
area, compared to consecutive physical adresses?

> I guess this wont be anymore a concern if I can finish my pending work
> about vmalloc() trying to get adjacent pages
> https://lkml.org/lkml/2016/12/21/285
> 
> Thanks.
> 
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__GFP_REPEAT usage in fq_alloc_node Michal Hocko <mhocko@kernel.org> - 2017-01-06 16:30 +0100
  Re: __GFP_REPEAT usage in fq_alloc_node Eric Dumazet <edumazet@google.com> - 2017-01-06 16:40 +0100
    Re: __GFP_REPEAT usage in fq_alloc_node Michal Hocko <mhocko@kernel.org> - 2017-01-06 17:10 +0100
      Re: __GFP_REPEAT usage in fq_alloc_node Michal Hocko <mhocko@kernel.org> - 2017-01-06 17:20 +0100
        Re: [PATCH] net: use kvmalloc rather than open coded variant kbuild test robot <lkp@intel.com> - 2017-01-07 04:40 +0100
          Re: [PATCH] net: use kvmalloc rather than open coded variant Michal Hocko <mhocko@kernel.org> - 2017-01-07 10:30 +0100
        Re: [PATCH] net: use kvmalloc rather than open coded variant kbuild test robot <lkp@intel.com> - 2017-01-07 04:40 +0100
        Re: __GFP_REPEAT usage in fq_alloc_node Michal Hocko <mhocko@kernel.org> - 2017-01-09 11:30 +0100
          Re: __GFP_REPEAT usage in fq_alloc_node Eric Dumazet <edumazet@google.com> - 2017-01-09 17:10 +0100
            Re: __GFP_REPEAT usage in fq_alloc_node Michal Hocko <mhocko@kernel.org> - 2017-01-09 18:50 +0100
              Re: __GFP_REPEAT usage in fq_alloc_node Eric Dumazet <edumazet@google.com> - 2017-01-09 19:00 +0100
      Re: [PATCH] net_sched: use kvmalloc rather than opencoded variant Michal Hocko <mhocko@kernel.org> - 2017-01-16 10:00 +0100
    Re: __GFP_REPEAT usage in fq_alloc_node Vlastimil Babka <vbabka@suse.cz> - 2017-01-06 17:40 +0100
      Re: __GFP_REPEAT usage in fq_alloc_node Eric Dumazet <edumazet@google.com> - 2017-01-06 17:50 +0100
        Re: __GFP_REPEAT usage in fq_alloc_node Vlastimil Babka <vbabka@suse.cz> - 2017-01-06 18:00 +0100
          Re: __GFP_REPEAT usage in fq_alloc_node Eric Dumazet <edumazet@google.com> - 2017-01-06 18:10 +0100
            Re: __GFP_REPEAT usage in fq_alloc_node Vlastimil Babka <vbabka@suse.cz> - 2017-01-06 18:20 +0100
        Re: __GFP_REPEAT usage in fq_alloc_node Eric Dumazet <edumazet@google.com> - 2017-01-06 18:00 +0100

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