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

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Date:	Tue, 19 Feb 2013 21:27:55 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
CC:	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mgorman@...e.de, kyungmin.park@...sung.com
Subject: Re: [PATCH] mm: cma: fix accounting of CMA pages placed in high memory

On 02/05/2013 03:10 PM, Marek Szyprowski wrote:
> Hello,
>
> On 2/5/2013 12:34 AM, Minchan Kim wrote:
>> On Mon, Feb 04, 2013 at 11:27:05AM +0100, Marek Szyprowski wrote:
>> > The total number of low memory pages is determined as
>> > totalram_pages - totalhigh_pages, so without this patch all CMA
>> > pageblocks placed in highmem were accounted to low memory.
>>
>> So what's the end user effect? With the effect, we have to decide
>> routing it on stable.
>>
>> >
>> > Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>> > ---
>> >  mm/page_alloc.c |    4 ++++
>> >  1 file changed, 4 insertions(+)
>> >
>> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> > index f5bab0a..6415d93 100644
>> > --- a/mm/page_alloc.c
>> > +++ b/mm/page_alloc.c
>> > @@ -773,6 +773,10 @@ void __init init_cma_reserved_pageblock(struct 
>> page *page)
>> >      set_pageblock_migratetype(page, MIGRATE_CMA);
>> >      __free_pages(page, pageblock_order);
>> >      totalram_pages += pageblock_nr_pages;
>> > +#ifdef CONFIG_HIGHMEM
>>
>> We don't need #ifdef/#endif.
>
> #ifdef is required to let this code compile when highmem is not enabled,
> becuase totalhigh_pages is defined as 0, see include/linux/highmem.h
>

Hi Marek,

1) Why can support CMA regions placed in highmem? CMA is for dma buffer, 
correct? Then how can old dma device access highmem?
2) Why there is no totalhigh_pages variable define in the case of config 
highmem?

>> > +    if (PageHighMem(page))
>> > +        totalhigh_pages += pageblock_nr_pages;
>> > +#endif
>> >  }
>> >  #endif
>> >
>
> Best regards

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