linux-kernel - Re: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning

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Message-ID: <98411844-19b7-a75b-d52c-6e2c46b40d57@intel.com>
Date:   Wed, 26 Sep 2018 08:41:29 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        pavel.tatashin@...rosoft.com, dave.jiang@...el.com,
        jglisse@...hat.com, rppt@...ux.vnet.ibm.com,
        dan.j.williams@...el.com, logang@...tatee.com, mingo@...nel.org,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling
 page init poisoning

On 09/26/2018 08:24 AM, Alexander Duyck wrote:
> With no options it works just like slub_debug and enables all
> available options. So in our case it is a NOP since we wanted the
> debugging enabled by default.

Yeah, but slub_debug is different.

First, nobody uses the slub_debug=- option because *that* is only used
when you have SLUB_DEBUG=y *and* CONFIG_SLUB_DEBUG_ON=y, which not even
Fedora does.

slub_debug is *primarily* for *adding* debug features.  For this, we
need to turn them off.

It sounds like following slub_debug was a bad idea, especially following
its semantics too closely when it doesn't make sense.