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    Subject[ 55/70] mm: setup pageblock_order before its used by sparsemem
    3.2-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Xishi Qiu <qiuxishi@huawei.com>

    commit ca57df79d4f64e1a4886606af4289d40636189c5 upstream.

    On architectures with CONFIG_HUGETLB_PAGE_SIZE_VARIABLE set, such as
    Itanium, pageblock_order is a variable with default value of 0. It's set
    to the right value by set_pageblock_order() in function
    free_area_init_core().

    But pageblock_order may be used by sparse_init() before free_area_init_core()
    is called along path:
    sparse_init()
    ->sparse_early_usemaps_alloc_node()
    ->usemap_size()
    ->SECTION_BLOCKFLAGS_BITS
    ->((1UL << (PFN_SECTION_SHIFT - pageblock_order)) *
    NR_PAGEBLOCK_BITS)

    The uninitialized pageblock_size will cause memory wasting because
    usemap_size() returns a much bigger value then it's really needed.

    For example, on an Itanium platform,
    sparse_init() pageblock_order=0 usemap_size=24576
    free_area_init_core() before pageblock_order=0, usemap_size=24576
    free_area_init_core() after pageblock_order=12, usemap_size=8

    That means 24K memory has been wasted for each section, so fix it by calling
    set_pageblock_order() from sparse_init().

    Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
    Signed-off-by: Jiang Liu <liuj97@gmail.com>
    Cc: Tony Luck <tony.luck@intel.com>
    Cc: Yinghai Lu <yinghai@kernel.org>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Keping Chen <chenkeping@huawei.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    [bwh: Backported to 3.2: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    mm/internal.h | 2 ++
    mm/page_alloc.c | 4 ++--
    mm/sparse.c | 3 +++
    3 files changed, 7 insertions(+), 2 deletions(-)

    --- a/mm/internal.h
    +++ b/mm/internal.h
    @@ -309,3 +309,5 @@ extern u64 hwpoison_filter_flags_mask;
    extern u64 hwpoison_filter_flags_value;
    extern u64 hwpoison_filter_memcg;
    extern u32 hwpoison_filter_enable;
    +
    +extern void set_pageblock_order(void);
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -4282,7 +4282,7 @@ static inline void setup_usemap(struct p
    #ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE

    /* Initialise the number of pages represented by NR_PAGEBLOCK_BITS */
    -static inline void __init set_pageblock_order(void)
    +void __init set_pageblock_order(void)
    {
    unsigned int order;

    @@ -4310,7 +4310,7 @@ static inline void __init set_pageblock_
    * include/linux/pageblock-flags.h for the values of pageblock_order based on
    * the kernel config
    */
    -static inline void set_pageblock_order(void)
    +void __init set_pageblock_order(void)
    {
    }

    --- a/mm/sparse.c
    +++ b/mm/sparse.c
    @@ -486,6 +486,9 @@ void __init sparse_init(void)
    struct page **map_map;
    #endif

    + /* Setup pageblock_order for HUGETLB_PAGE_SIZE_VARIABLE */
    + set_pageblock_order();
    +
    /*
    * map is using big page (aka 2M in x86 64 bit)
    * usemap is less one page (aka 24 bytes)



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