mm/memcg: optimize user context object stock access

Most kmem_cache_alloc() calls are from user context.  With instrumentation
enabled, the measured amount of kmem_cache_alloc() calls from non-task
context was about 0.01% of the total.

The irq disable/enable sequence used in this case to access content from
object stock is slow.  To optimize for user context access, there are now
two sets of object stocks (in the new obj_stock structure) for task
context and interrupt context access respectively.

The task context object stock can be accessed after disabling preemption
which is cheap in non-preempt kernel.  The interrupt context object stock
can only be accessed after disabling interrupt.  User context code can
access interrupt object stock, but not vice versa.

The downside of this change is that there are more data stored in local
object stocks and not reflected in the charge counter and the vmstat
arrays.  However, this is a small price to pay for better performance.

[[email protected]: fix potential uninitialized variable warning]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: coding style fixes]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Waiman Long <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Alex Shi <[email protected]>
Cc: Chris Down <[email protected]>
Cc: Yafang Shao <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Masayoshi Mizuma <[email protected]>
Cc: Xing Zhengjun <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions