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Subject: Re: [PATCH v4 01/11] powerpc/mm: Adds counting method to monitor
 lockless pgtable walks
From: John Hubbard <jhubbard@nvidia.com>
To: Leonardo Bras <leonardo@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>,
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On 9/29/19 3:40 PM, John Hubbard wrote:
> On 9/27/19 4:39 PM, Leonardo Bras wrote:
...
> +config LOCKLESS_PAGE_TABLE_WALK_TRACKING
> +=C2=A0=C2=A0=C2=A0 bool "Tracking (and optimization) of lockless page ta=
ble walkers"
> +=C2=A0=C2=A0=C2=A0 default n
> +
> +=C2=A0=C2=A0=C2=A0 help
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Maintain a reference count of active lock=
less page table
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 walkers. This adds 4 bytes to struct mm s=
ize, and two atomic
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 operations to calls such as get_user_page=
s_fast(). Some
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 architectures can optimize page table ope=
rations if this
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 is enabled.
> +
>  =C2=A0endmenu

Actually, the above should be an internal-only config option (PPC arch can
auto-select it), so just:

+config LOCKLESS_PAGE_TABLE_WALK_TRACKING
+	bool

...because it's entirely up to other code (as opposed to other people)
as to whether this should be selected.

I got carried away. :)

thanks,
--=20
John Hubbard
NVIDIA