linux-kernel - Re: [PATCH] vmstat: Keep count of the maximum page reached by the kernel stack

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Date: Thu, 14 Mar 2024 08:19:20 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Pasha Tatashin <pasha.tatashin@...een.com>, "akpm@...ux-foundation.org"
	<akpm@...ux-foundation.org>, "jpoimboe@...nel.org" <jpoimboe@...nel.org>,
	"kent.overstreet@...ux.dev" <kent.overstreet@...ux.dev>,
	"peterz@...radead.org" <peterz@...radead.org>, "nphamcs@...il.com"
	<nphamcs@...il.com>, "cerasuolodomenico@...il.com"
	<cerasuolodomenico@...il.com>, "surenb@...gle.com" <surenb@...gle.com>,
	"lizhijian@...itsu.com" <lizhijian@...itsu.com>, "willy@...radead.org"
	<willy@...radead.org>, "shakeel.butt@...ux.dev" <shakeel.butt@...ux.dev>,
	"vbabka@...e.cz" <vbabka@...e.cz>, "ziy@...dia.com" <ziy@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] vmstat: Keep count of the maximum page reached by the
 kernel stack



Le 13/03/2024 à 04:34, Pasha Tatashin a écrit :
> CONFIG_DEBUG_STACK_USAGE provides a mechanism to know the minimum amount
> of memory that was left in stack. Every time the new anti-record is
> reached a message is printed to the console.
> 
> However, this is not useful to know how much each page within stack was
> actually used. Provide a mechanism to count the number of time each
> stack page was reached throughout the live of the stack:

by "this is not useful to know ", you mean "this does not allow us to 
know" ?

> 
> 	$ grep kstack /proc/vmstat
> 	kstack_page_1 19974
> 	kstack_page_2 94
> 	kstack_page_3 0
> 	kstack_page_4 0

That's probably only usefull when THREAD_SIZE is larger than PAGE_SIZE.

On powerpc 8xx, THREAD_SIZE is 8k by default and PAGE_SIZE can be either 
4k or 16k.

Christophe