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    Subject[PATCH v5 2/5] arm: arm64: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()
    Date
    Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
    where possible") optimized the loop in memmap_init_zone(). But there is
    still some room for improvement. E.g. if pfn and pfn+1 are in the same
    memblock region, we can simply pfn++ instead of doing the binary search
    in memblock_next_valid_pfn.

    Signed-off-by: Jia He <jia.he@hxt-semitech.com>
    ---
    arch/arm/include/asm/page.h | 1 +
    arch/arm/mm/init.c | 28 ++++++++++++++++++++++------
    arch/arm64/include/asm/page.h | 1 +
    arch/arm64/mm/init.c | 28 ++++++++++++++++++++++------
    4 files changed, 46 insertions(+), 12 deletions(-)

    diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
    index 489875c..f38909c 100644
    --- a/arch/arm/include/asm/page.h
    +++ b/arch/arm/include/asm/page.h
    @@ -157,6 +157,7 @@ extern void copy_page(void *to, const void *from);
    typedef struct page *pgtable_t;

    #ifdef CONFIG_HAVE_ARCH_PFN_VALID
    +extern int early_region_idx;
    extern int pfn_valid(unsigned long);
    extern unsigned long memblock_next_valid_pfn(unsigned long pfn);
    #define skip_to_last_invalid_pfn(pfn) (memblock_next_valid_pfn(pfn) - 1)
    diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
    index 0fb85ca..06ed190 100644
    --- a/arch/arm/mm/init.c
    +++ b/arch/arm/mm/init.c
    @@ -193,6 +193,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
    }

    #ifdef CONFIG_HAVE_ARCH_PFN_VALID
    +int early_region_idx __meminitdata = -1;
    +
    int pfn_valid(unsigned long pfn)
    {
    return memblock_is_map_memory(__pfn_to_phys(pfn));
    @@ -203,28 +205,42 @@ EXPORT_SYMBOL(pfn_valid);
    unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
    {
    struct memblock_type *type = &memblock.memory;
    + struct memblock_region *regions = type->regions;
    unsigned int right = type->cnt;
    unsigned int mid, left = 0;
    + unsigned long start_pfn, end_pfn;
    phys_addr_t addr = PFN_PHYS(++pfn);

    + /* fast path, return pfn+1 if next pfn is in the same region */
    + if (early_region_idx != -1) {
    + start_pfn = PFN_DOWN(regions[early_region_idx].base);
    + end_pfn = PFN_DOWN(regions[early_region_idx].base +
    + regions[early_region_idx].size);
    +
    + if (pfn >= start_pfn && pfn < end_pfn)
    + return pfn;
    + }
    +
    + /* slow path, do the binary searching */
    do {
    mid = (right + left) / 2;

    - if (addr < type->regions[mid].base)
    + if (addr < regions[mid].base)
    right = mid;
    - else if (addr >= (type->regions[mid].base +
    - type->regions[mid].size))
    + else if (addr >= (regions[mid].base + regions[mid].size))
    left = mid + 1;
    else {
    - /* addr is within the region, so pfn is valid */
    + early_region_idx = mid;
    return pfn;
    }
    } while (left < right);

    if (right == type->cnt)
    return -1UL;
    - else
    - return PHYS_PFN(type->regions[right].base);
    +
    + early_region_idx = right;
    +
    + return PHYS_PFN(regions[early_region_idx].base);
    }
    EXPORT_SYMBOL(memblock_next_valid_pfn);
    #endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
    diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
    index e57d3f2..f0d8c8e5 100644
    --- a/arch/arm64/include/asm/page.h
    +++ b/arch/arm64/include/asm/page.h
    @@ -38,6 +38,7 @@ extern void clear_page(void *to);
    typedef struct page *pgtable_t;

    #ifdef CONFIG_HAVE_ARCH_PFN_VALID
    +extern int early_region_idx;
    extern int pfn_valid(unsigned long);
    extern unsigned long memblock_next_valid_pfn(unsigned long pfn);
    #define skip_to_last_invalid_pfn(pfn) (memblock_next_valid_pfn(pfn) - 1)
    diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
    index 13e43ff..342e4e2 100644
    --- a/arch/arm64/mm/init.c
    +++ b/arch/arm64/mm/init.c
    @@ -285,6 +285,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
    #endif /* CONFIG_NUMA */

    #ifdef CONFIG_HAVE_ARCH_PFN_VALID
    +int early_region_idx __meminitdata = -1;
    +
    int pfn_valid(unsigned long pfn)
    {
    return memblock_is_map_memory(pfn << PAGE_SHIFT);
    @@ -295,28 +297,42 @@ EXPORT_SYMBOL(pfn_valid);
    unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
    {
    struct memblock_type *type = &memblock.memory;
    + struct memblock_region *regions = type->regions;
    unsigned int right = type->cnt;
    unsigned int mid, left = 0;
    + unsigned long start_pfn, end_pfn;
    phys_addr_t addr = PFN_PHYS(++pfn);

    + /* fast path, return pfn+1 if next pfn is in the same region */
    + if (early_region_idx != -1) {
    + start_pfn = PFN_DOWN(regions[early_region_idx].base);
    + end_pfn = PFN_DOWN(regions[early_region_idx].base +
    + regions[early_region_idx].size);
    +
    + if (pfn >= start_pfn && pfn < end_pfn)
    + return pfn;
    + }
    +
    + /* slow path, do the binary searching */
    do {
    mid = (right + left) / 2;

    - if (addr < type->regions[mid].base)
    + if (addr < regions[mid].base)
    right = mid;
    - else if (addr >= (type->regions[mid].base +
    - type->regions[mid].size))
    + else if (addr >= (regions[mid].base + regions[mid].size))
    left = mid + 1;
    else {
    - /* addr is within the region, so pfn is valid */
    + early_region_idx = mid;
    return pfn;
    }
    } while (left < right);

    if (right == type->cnt)
    return -1UL;
    - else
    - return PHYS_PFN(type->regions[right].base);
    +
    + early_region_idx = right;
    +
    + return PHYS_PFN(regions[early_region_idx].base);
    }
    EXPORT_SYMBOL(memblock_next_valid_pfn);
    #endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
    --
    2.7.4
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