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

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Message-ID:
 <TYZP153MB07963DDE4B7E01C575B143E2BE882@TYZP153MB0796.APCP153.PROD.OUTLOOK.COM>
Date: Fri, 23 Aug 2024 09:30:29 +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>, "clameter@....com" <clameter@....com>,
	"mgorman@...hsingularity.net" <mgorman@...hsingularity.net>
Subject: RE: [PATCH v2] mm/vmstat: Defer the refresh_zone_stat_thresholds
 after all CPUs bringup



> -----Original Message-----
> From: Saurabh Sengar <ssengar@...ux.microsoft.com>
> Sent: 12 August 2024 11:44
> To: akpm@...ux-foundation.org; linux-mm@...ck.org; linux-
> kernel@...r.kernel.org
> Cc: Saurabh Singh Sengar <ssengar@...rosoft.com>; wei.liu@...nel.org;
> srivatsa@...il.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@...ux.microsoft.com>

CC: Mel Gorman and Christoph Lameter