lkml.org 
[lkml]   [2015]   [Oct]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [Patch V3 2/9] kernel/profile.c: Replace cpu_to_mem() with cpu_to_node()
From
Date
On 2015/8/20 8:00, David Rientjes wrote:
> On Wed, 19 Aug 2015, Jiang Liu wrote:
>
>> On 2015/8/18 8:31, David Rientjes wrote:
>>> On Mon, 17 Aug 2015, Jiang Liu wrote:
>>>
>>>> Function profile_cpu_callback() allocates memory without specifying
>>>> __GFP_THISNODE flag, so replace cpu_to_mem() with cpu_to_node()
>>>> because cpu_to_mem() may cause suboptimal memory allocation if
>>>> there's no free memory on the node returned by cpu_to_mem().
>>>>
>>>
>>> Why is cpu_to_node() better with regard to free memory and NUMA locality?
>> Hi David,
>> Thanks for review. This is a special case pointed out by Tejun.
>> For the imagined topology, A<->B<->X<->C<->D, where A, B, C, D has
>> memory and X is memoryless.
>> Possible fallback lists are:
>> B: [ B, A, C, D]
>> X: [ B, C, A, D]
>> C: [ C, D, B, A]
>>
>> cpu_to_mem(X) will either return B or C. Let's assume it returns B.
>> Then we will use "B: [ B, A, C, D]" to allocate memory for X, which
>> is not the optimal fallback list for X. And cpu_to_node(X) returns
>> X, and "X: [ B, C, A, D]" is the optimal fallback list for X.
>
> Ok, that makes sense, but I would prefer that this
> alloc_pages_exact_node() change to alloc_pages_node() since, as you
> mention in your commit message, __GFP_THISNODE is not set.
Hi David,
Sorry for slow response due to personal reasons!
Function alloc_pages_exact_node() has been renamed as
__alloc_pages_node() by commit 96db800f5d73, and __alloc_pages_node()
is a slightly optimized version of alloc_pages_node() which doesn't
fallback to current node for nid == NUMA_NO_NODE case. So it would
be better to keep using __alloc_pages_node() because cpu_to_node()
always returns valid node id.
Thanks!
Gerry

>
> In the longterm, if we setup both zonelists correctly (no __GFP_THISNODE
> and with __GFP_THISNODE), then I'm not sure there's any reason to ever use
> cpu_to_mem() for alloc_pages().
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>


\
 
 \ /
  Last update: 2015-10-09 05:01    [W:0.162 / U:0.776 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site