Re: [PATCH/RFC] mm/debug_pagealloc: enable it by default

From: Christian Borntraeger
Date: Mon Jan 25 2016 - 14:52:11 EST


On 01/25/2016 08:38 PM, Dave Jones wrote:
> Content preview: On Mon, Jan 25, 2016 at 02:22:10PM -0500, Dave Jones wrote:
> > > A default mode would be ok for me as it makes things obvious. Will send
> > > a patch. > > The messaging around changing a default like this was really
> poor. > When we do behaviour changes like this, we typically rename the CONFIG
> option > to make it obvious that things aren't as they used to be. [...]
>
> Content analysis details: (-2.9 points, 5.0 required)
>
> pts rule name description
> ---- ---------------------- --------------------------------------------------
> -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP
> -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1%
> [score: 0.0000]
> X-ZLA-Header: unknown; 0
> X-ZLA-DetailInfo: BA=6.00004114; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZH=6.00000000; ZP=6.00000000; ZU=6.00000002; UDB=6.00294159; UTC=2016-01-25 19:38:24
> x-cbid: 16012519-0041-0000-0000-0000074865D5
> X-IBM-ISS-SpamDetectors: Score=0.40962; FLB=0; FLI=0; BY=0; FL=0; FP=0; FZ=0;
> HX=0; KW=0; PH=0; RB=0; SC=0.40962; ST=0; TS=0; UL=0; ISC=
> X-IBM-ISS-DetailInfo: BY=3.00004831; HX=3.00000240; KW=3.00000007;
> PH=3.00000004; SC=3.00000137; SDB=6.00650474; UDB=6.00294159; UTC=2016-01-25
> 19:38:24
> X-TM-AS-MML: disable
>
> On Mon, Jan 25, 2016 at 02:22:10PM -0500, Dave Jones wrote:
>
> > > A default mode would be ok for me as it makes things obvious. Will send
> > > a patch.
> >
> > The messaging around changing a default like this was really poor.
> > When we do behaviour changes like this, we typically rename the CONFIG option
> > to make it obvious that things aren't as they used to be.
>
> Looking at this closer, shouldn't the original diff to make this runtime
> have also changed the x86 implementation details in arch/x86/mm/pageattr.c ?
> Even when we don't boot with the enable flag, we're doing the "split 2M page into 4Ks"
> thing. It looks like a s/debug_pagealloc/debug_pagealloc_enabled()/ might
> do the right thing maybe ?

I have some patches ready, that fix the identity mapping for s390 and x86. sparc
is hard to do as it allocates the TSB very early. Will send around what I have soon.