KOSAKI Motohiro wrote:
>> Then we have another mechanism that will avoid
>> off node memory references by allocating new slabs. Can you set the
>> node_defrag parameter to 0? (Noted by Adrian).
>
> Please let me know that operations ?
The control over the preferences of node local vs. remote defrag is occurring
via /sys/kernel/slab/<slabcache>/remote_node_defrag ratio. Default is 10%.
Comments in get_any_partial explain the operations.
The default setting means that in 9 out of 10 cases slub will prefer creating
a new slab over taking one from the remote node (meaning the memory is node
local, probably not important in your 2 node case). It will therefore waste
memory because local memory may be more efficient to use.
Setting remote_node_defrag_ratio to 100 will make slub always take the remote
slab instead of allocating a new one.
/*
* The defrag ratio allows a configuration of the tradeoffs between
* inter node defragmentation and node local allocations. A lower
* defrag_ratio increases the tendency to do local allocations
* instead of attempting to obtain partial slabs from other nodes.
*
* If the defrag_ratio is set to 0 then kmalloc() always
* returns node local objects. If the ratio is higher then kmalloc()
* may return off node objects because partial slabs are obtained
* from other nodes and filled up.
*
* If /sys/kernel/slab/xx/defrag_ratio is set to 100 (which makes
* defrag_ratio = 1000) then every (well almost) allocation will
* first attempt to defrag slab caches on other nodes. This means
* scanning over all nodes to look for partial slabs which may be
* expensive if we do it every time we are trying to find a slab
* with available objects.
*/
if (!s->remote_node_defrag_ratio ||
get_cycles() % 1024 > s->remote_node_defrag_ratio)
return NULL;
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