Re: CMA and zone watermarks

Minchan Kim
2012-10-09T04:39:11Z

On Tue, Oct 09, 2012 at 05:12:21AM +0200, Marek Szyprowski wrote:
> Hello,
>
> On 10/9/2012 5:10 AM, Minchan Kim wrote:
>
> >On Mon, Oct 08, 2012 at 05:41:14PM +0200, Rabin Vincent wrote:
> >>It appears that when CMA is enabled, the zone watermarks are not properly
> >>respected, leading to for example GFP_NOWAIT allocations getting access to the
> >>high pools.
> >>
> >>I ran the following test code which simply allocates pages with GFP_NOWAIT
> >>until it fails, and then tries GFP_ATOMIC. Without CMA, the GFP_ATOMIC
> >>allocation succeeds, with CMA, it fails too.
> >
> >Good spot. By wrong zone_watermark_check, it can consume reserved memory pool.
>
> That was the main reason for the Bartek's research.

Okay. It shoud have written down for more good description at that time. :)

>
> >>Logs attached (includes my patch which prints the migration type in the failure
> >>message http://marc.info/?l=linux-mm&m=134971041701306&w=2), taken on 3.6
> >>kernel.
> >>
> >
> >Fortunately, recently, Bart sent a patch about that.
> >http://marc.info/?l=linux-mm&m=134763299016693&w=2
> >
> >Could you test above patches in your kernel?
> >You have to apply [2/4], [3/4], [4/4] and don't need [1/4].
>
> AFAIR without patch [1/4], free cma page counter will go below zero
> and weird thing will happen, so better apply the complete patchset.

I can't understand your point. [1/4] is just fix for correcting trace
No?

http://marc.info/?l=linux-mm&m=134763301216713&w=2

>
> Best regards
> --
> Marek Szyprowski
> Samsung Poland R&D Center
>
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--
Kind regards,
Minchan Kim