linux-kernel - Re: [PATCH] mm: cma: fix accounting of CMA pages placed in high memory

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Date:	Tue, 5 Feb 2013 17:47:05 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	Kyungmin Park <kmpark@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mgorman@...e.de
Subject: Re: [PATCH] mm: cma: fix accounting of CMA pages placed in high
 memory

On Tue, Feb 05, 2013 at 09:38:30AM +0100, Marek Szyprowski wrote:
> Hello,
> 
> On 2/5/2013 1:40 AM, Minchan Kim wrote:
> 
> ...
> 
> >> Previous time, it's not fully tested and now we checked it with
> >> highmem support patches.
> >
> >I get it. Sigh. then [1] inline attached below wan't good.
> >We have to code like this?
> >
> >[1] 6a6dccba, mm: cma: don't replace lowmem pages with highmem
> >
> >diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >index b97cf12..0707e0a 100644
> >--- a/mm/page_alloc.c
> >+++ b/mm/page_alloc.c
> >@@ -5671,11 +5671,10 @@ static struct page *
> >  __alloc_contig_migrate_alloc(struct page *page, unsigned long private,
> >                              int **resultp)
> >  {
> >-       gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
> >-
> >-       if (PageHighMem(page))
> >-               gfp_mask |= __GFP_HIGHMEM;
> >-
> >+       gfp_t gfp_mask = GFP_HIGHUSER_MOVABLE;
> >+       struct address_space *mapping = page_mapping(page);
> >+       if (mapping)
> >+               gfp_mask = mapping_gfp_mask(mapping);
> >         return alloc_page(gfp_mask);
> >  }
> 
> Am I right that this code will allocate more pages from himem? Old approach

Yes.

> never migrate lowmem page to himem, what is now possible as gfp mask
> is always
> taken from mapping_gfp flags. I only wonder if forcing GFP_HIGHUSER_MOVABLE

-ENOPARSE. What is not possbile ~~ take from mapping_gfp flags.
Could you clarify your statement?

> for pages without the mapping is a correct. Shouldn't we use avoid himem in

CMA pages is for pages for user, NOT kernel so HIGHUSER_MOVABLE makes sense.

> such case?

I don't get it. :(
We have to recomment use of highmem for user space pages.
Am I missing something?

Sorry, I should go out of office now so forgive my late response.



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