linux-kernel - Re: [PATCH 1/4] mm: Provide kernel parameter to allow disabling page init poisoning

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Date:   Wed, 12 Sep 2018 08:23:58 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Alexander Duyck <alexander.duyck@...il.com>, mhocko@...nel.org
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-nvdimm@...ts.01.org, pavel.tatashin@...rosoft.com,
        dave.jiang@...el.com, Ingo Molnar <mingo@...nel.org>,
        jglisse@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
        logang@...tatee.com, dan.j.williams@...el.com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 1/4] mm: Provide kernel parameter to allow disabling page
 init poisoning

On 09/12/2018 07:49 AM, Alexander Duyck wrote:
>>> +     page_init_poison=       [KNL] Boot-time parameter changing the
>>> +                     state of poisoning of page structures during early
>>> +                     boot. Used to verify page metadata is not accessed
>>> +                     prior to initialization. Available with
>>> +                     CONFIG_DEBUG_VM=y.
>>> +                     off: turn off poisoning
>>> +                     on: turn on poisoning (default)
>>> +
>> what about the following wording or something along those lines
>>
>> Boot-time parameter to control struct page poisoning which is a
>> debugging feature to catch unitialized struct page access. This option
>> is available only for CONFIG_DEBUG_VM=y and it affects boot time
>> (especially on large systems). If there are no poisoning bugs reported
>> on the particular system and workload it should be safe to disable it to
>> speed up the boot time.
> That works for me. I will update it for the next release.

FWIW, I rather liked Dan's idea of wrapping this under
vm_debug=<something>.  We've got a zoo of boot options and it's really
hard to _remember_ what does what.  For this case, we're creating one
that's only available under a specific debug option and I think it makes
total sense to name the boot option accordingly.

For now, I think it makes total sense to do vm_debug=all/off.  If, in
the future, we get more options, we can do things like slab does and do
vm_debug=P (for Page poison) for this feature specifically.

	vm_debug =	[KNL] Available with CONFIG_DEBUG_VM=y.
			May slow down boot speed, especially on larger-
			memory systems when enabled.
			off: turn off all runtime VM debug features
			all: turn on all debug features (default)