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

From: Simon Jeons
Date: Wed Feb 20 2013 - 00:31:57 EST

On 02/20/2013 10:57 AM, Kyungmin Park wrote:
On Tue, Feb 19, 2013 at 10:27 PM, Simon Jeons <simon.jeons@xxxxxxxxx> wrote:
On 02/05/2013 03:10 PM, Marek Szyprowski wrote:

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@xxxxxxxxxxx>
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;
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?
Some vendors use reserved memory at highmem, and it's hard to modify
to use lowmem, so just CMA can support highmem and no need to adjust
address used at reserved memory.
CMA is for dma buffer, correct? Then how can old dma device access highmem?
What's the "old dma device"? To support it, we also modify

I mean dma devices which should still use bounce buffer, then these devices will use bounce buffer to access CMA region in highmem or ...?

arch/arm/mm/dma-mapping.c for handling highmem address.

2) Why there is no totalhigh_pages variable define in the case of config
I don't know. it's just defined in case of highmem. that's reason to
use #ifdef/endif. we don't know hisotrical reason.

Thank you,
Kyungmin Park

+ if (PageHighMem(page))
+ totalhigh_pages += pageblock_nr_pages;

Best regards

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