linux-kernel - RE: [PATCH v2] mm/vmstat: Defer the refresh_zone_stat

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Message-ID:
 <SEZP153MB0791CB961FF0D1512DC47164BE632@SEZP153MB0791.APCP153.PROD.OUTLOOK.COM>
Date: Thu, 19 Sep 2024 19:52:45 +0000
From: Saurabh Singh Sengar <ssengar@...rosoft.com>
To: Saurabh Sengar <ssengar@...ux.microsoft.com>, "akpm@...ux-foundation.org"
	<akpm@...ux-foundation.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "wei.liu@...nel.org" <wei.liu@...nel.org>, "srivatsa@...il.mit.edu"
	<srivatsa@...il.mit.edu>, "mgorman@...hsingularity.net"
	<mgorman@...hsingularity.net>, "cl@...ux.com" <cl@...ux.com>
Subject: RE: [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@...ux.microsoft.com>
> >
> > CC: Mel Gorman and Christoph Lameter
> 
> 
> Adding cl@...ux.com instead of clameter@....com for Christoph Lameter
> 
> - Saurabh

Hi Andrew,

Can we get this merge in for next kernel release.
Please let me know if there is any concern with this patch.

Regards,
Saurabh