linux-kernel - Re: [PATCH V6] x86/mm: Tracking linear mapping split events

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Date:   Fri, 5 Mar 2021 16:57:15 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Saravanan D <saravanand@...com>
Cc:     <mingo@...hat.com>, <x86@...nel.org>,
        <dave.hansen@...ux.intel.com>, <tj@...nel.org>,
        <hannes@...xchg.org>, <linux-kernel@...r.kernel.org>,
        <kernel-team@...com>
Subject: Re: [PATCH V6] x86/mm: Tracking linear mapping split events

On Thu, 18 Feb 2021 15:57:44 -0800 Saravanan D <saravanand@...com> wrote:

> To help with debugging the sluggishness caused by TLB miss/reload,
> we introduce monotonic hugepage [direct mapped] split event counts since
> system state: SYSTEM_RUNNING to be displayed as part of
> /proc/vmstat in x86 servers
>
> ...
>
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -120,6 +120,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>  #ifdef CONFIG_SWAP
>  		SWAP_RA,
>  		SWAP_RA_HIT,
> +#endif
> +#ifdef CONFIG_X86
> +		DIRECT_MAP_LEVEL2_SPLIT,
> +		DIRECT_MAP_LEVEL3_SPLIT,
>  #endif
>  		NR_VM_EVENT_ITEMS
>  };

This is the first appearance of arch-specific fields in /proc/vmstat.

I don't really see a problem with this - vmstat is basically a dumping
ground of random developer stuff.  But was this the best place in which
to present this data?