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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 <> wrote:

    > Kukjin reported oops happen while he change min_free_kbytes
    > 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 <>
    > Signed-off-by: KAMEZAWA Hiroyuki <>
    > Reported-by: Kukjin Kim <>

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


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