Re: [PATCH 5/5] mm/memcg: Optimize user context object stock access

[Waiman Long]

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