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SubjectRe: [PATCH] Tight check of pfn_valid on sparsemem - v2
On Sun, 18 Jul 2010 19:18:31 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:

> Kukjin reported oops happen while he change min_free_kbytes
> http://www.spinics.net/lists/arm-kernel/msg92894.html
> It happen by memory map on sparsemem.
>
> The system has a memory map following as.
> section 0 section 1 section 2
> 0x20000000-0x25000000, 0x40000000-0x50000000, 0x50000000-0x58000000
> SECTION_SIZE_BITS 28(256M)
>
> It means section 0 is an incompletely filled section.
> Nontheless, current pfn_valid of sparsemem checks pfn loosely.
> It checks only mem_section's validation but ARM can free mem_map on hole
> to save memory space. So in above case, pfn on 0x25000000 can pass pfn_valid's
> validation check. It's not what we want.
>
> We can match section size to smallest valid size.(ex, above case, 16M)
> But Russell doesn't like it due to mem_section's memory overhead with different
> configuration(ex, 512K section).
>
> I tried to add valid pfn range in mem_section but everyone doesn't like it
> due to size overhead. This patch is suggested by KAMEZAWA-san.
> I just fixed compile error and change some naming.
>
> This patch registers address of mem_section to memmap itself's page struct's
> pg->private field. This means the page is used for memmap of the section.
> Otherwise, the page is used for other purpose and memmap has a hole.
>
> This patch is based on mmotm-2010-07-01-12-19.
>
> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Reported-by: Kukjin Kim <kgene.kim@samsung.com>

Thank you for working on this. I myself like this solution.
I think ARM guys can make this default later (after rc period ?)

Thanks,
-Kame



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