RE: [PATCH v2] mm/vmstat: Defer the refresh_zone_stat_thresholds after all CPUs bringup

[Saurabh Singh Sengar <ssengar@microsoft.com>]

> -----Original Message-----
> From: Saurabh Singh Sengar <ssengar@microsoft.com>
> Sent: 23 August 2024 15:00
> To: Saurabh Sengar <ssengar@linux.microsoft.com>; akpm@linux-
> foundation.org; linux-mm@kvack.org; linux-kernel@vger.kernel.org
> Cc: wei.liu@kernel.org; srivatsa@csail.mit.edu; clameter@sgi.com;
> mgorman@techsingularity.net
> Subject: [EXTERNAL] RE: [PATCH v2] mm/vmstat: Defer the
> refresh_zone_stat_thresholds after all CPUs bringup
> 
> 
> 
> > -----Original Message-----
> > From: Saurabh Sengar <ssengar@linux.microsoft.com>
> > Sent: 12 August 2024 11:44
> > To: akpm@linux-foundation.org; linux-mm@kvack.org; linux-
> > kernel@vger.kernel.org
> > Cc: Saurabh Singh Sengar <ssengar@microsoft.com>; wei.liu@kernel.org;
> > srivatsa@csail.mit.edu
> > Subject: [PATCH v2] mm/vmstat: Defer the refresh_zone_stat_thresholds
> > after all CPUs bringup
> >
> > refresh_zone_stat_thresholds function has two loops which is expensive
> > for higher number of CPUs and NUMA nodes.
> >
> > Below is the rough estimation of total iterations done by these loops
> > based on number of NUMA and CPUs.
> >
> > Total number of iterations: nCPU * 2 * Numa * mCPU
> > Where:
> >  nCPU = total number of CPUs
> >  Numa = total number of NUMA nodes
> >  mCPU = mean value of total CPUs (e.g., 512 for 1024 total CPUs)
> >
> > For the system under test with 16 NUMA nodes and 1024 CPUs, this
> > results in a substantial increase in the number of loop iterations
> > during boot-up when NUMA is enabled:
> >
> > No NUMA = 1024*2*1*512  =   1,048,576 : Here
> refresh_zone_stat_thresholds
> > takes around 224 ms total for all the CPUs in the system under test.
> > 16 NUMA = 1024*2*16*512 =  16,777,216 : Here
> > refresh_zone_stat_thresholds takes around 4.5 seconds total for all
> > the CPUs in the system under test.
> >
> > Calling this for each CPU is expensive when there are large number of
> > CPUs along with multiple NUMAs. Fix this by deferring
> > refresh_zone_stat_thresholds to be called later at once when all the
> > secondary CPUs are up. Also, register the DYN hooks to keep the
> > existing hotplug functionality intact.
> >
> > Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> 
> CC: Mel Gorman and Christoph Lameter


Adding cl@linux.com instead of clameter@sgi.com for Christoph Lameter

- Saurabh