Re: CMA and zone watermarks

From: Marek Szyprowski
Date: Tue Oct 09 2012 - 01:15:47 EST


Hello,

On 10/9/2012 7:07 AM, Minchan Kim wrote:
On Tue, Oct 09, 2012 at 06:53:29AM +0200, Marek Szyprowski wrote:
Hello,

On 10/9/2012 6:43 AM, Minchan Kim wrote:
On Tue, Oct 09, 2012 at 05:12:21AM +0200, Marek Szyprowski wrote:
On 10/9/2012 5:10 AM, Minchan Kim wrote:
On Mon, Oct 08, 2012 at 05:41:14PM +0200, Rabin Vincent wrote:

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?

I just remember we ran into such strange negative number of free cma
pages issue without that patch, but maybe the final patchset will
simply fail to apply without the first patch.

I have no objection to apply them all, of course.
But note that if you suffer from such strange bug without [1/4],
it should be dug in without buring into just "fixing of the trace"
comment. As I saw the code without [1/4], I can't find any fault.
Could you elaborate it more if you have any guessing in mind?

I remember that in one version of the Bartek's patches, page_private(page) has been used directly for getting the migratetype after a call to __free_one_page() (the same way as trace_mm_page_pcpu_drain() used it), what resulted in incorrect counting of free pages. The issue has been fixed then by the patch [1/4].

Now I've check that the next patches use mt variable instead of page_private(page), so they will simply not apply without [1/4]. No other issues should be expected. I'm sorry for confusion.

Best regards
--
Marek Szyprowski
Samsung Poland R&D Center
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