> -----Original Message----- > From: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx> > Sent: 12 August 2024 11:44 > To: akpm@xxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx > Cc: Saurabh Singh Sengar <ssengar@xxxxxxxxxxxxx>; wei.liu@xxxxxxxxxx; > srivatsa@xxxxxxxxxxxxx > 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@xxxxxxxxxxxxxxxxxxx> CC: Mel Gorman and Christoph Lameter
