linux-kernel - Re: [PATCH V3] x86/mm: Tracking linear mapping split events

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Date:   Wed, 27 Jan 2021 15:00:11 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Saravanan D <saravanand@...com>, x86@...nel.org,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH V3] x86/mm: Tracking linear mapping split events

On 1/27/21 2:50 PM, Saravanan D wrote:
> To help with debugging the sluggishness caused by TLB miss/reload,
> we introduce monotonic lifetime hugepage split event counts since
> system state: SYSTEM_RUNNING to be displayed as part of
> /proc/vmstat in x86 servers
> 
> The lifetime split event information will be displayed at the bottom of
> /proc/vmstat
> ....
> swap_ra 0
> swap_ra_hit 0
> direct_map_2M_splits 167
> direct_map_1G_splits 6
> nr_unstable 0
> ....
> 
> One of the many lasting (as we don't coalesce back) sources for huge page
> splits is tracing as the granular page attribute/permission changes would
> force the kernel to split code segments mapped to huge pages to smaller
> ones thereby increasing the probability of TLB miss/reload even after
> tracing has been stopped.
> 
> Signed-off-by: Saravanan D <saravanand@...com>
> ---
>  arch/x86/mm/pat/set_memory.c  | 18 ++++++++++++++++++
>  include/linux/vm_event_item.h |  8 ++++++++
>  mm/vmstat.c                   |  8 ++++++++
>  3 files changed, 34 insertions(+)

Documenation/ update, please.

-- 
~Randy