On 4/12/21 2:55 PM, Roman Gushchin wrote:
On Fri, Apr 09, 2021 at 07:18:42PM -0400, Waiman Long wrote:
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 object stocks 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 mod_objcg_state() function is also modified to make sure that memcg
and lruvec stat updates are done with interrupted disabled.
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.
I agree, the extra memory space is not a significant concern.
I'd be more worried about the code complexity, but the result looks
nice to me!
Acked-by: Roman Gushchin <guro@xxxxxx>
Btw, it seems that the mm tree ran a bit off, so I had to apply this series
on top of Linus's tree to review. Please, rebase.
This patchset is based on the code in Linus' tree. I had applied the
patchset to linux-next to see if there was any conflicts. Two of the
patches had minor fuzzes around the edge but no actual merge conflict
for now.
Cheers,
Longman
