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    Subject[PATCH 4.19 189/195] mm: return zero_resv_unavail optimization
    Date
    From: Pavel Tatashin <pavel.tatashin@microsoft.com>

    [ Upstream commit ec393a0f014eaf688a3dbe8c8a4cbb52d7f535f9 ]

    When checking for valid pfns in zero_resv_unavail(), it is not necessary
    to verify that pfns within pageblock_nr_pages ranges are valid, only the
    first one needs to be checked. This is because memory for pages are
    allocated in contiguous chunks that contain pageblock_nr_pages struct
    pages.

    Link: http://lkml.kernel.org/r/20181002143821.5112-3-msys.mizuma@gmail.com
    Signed-off-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
    Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
    Reviewed-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
    Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Reviewed-by: Oscar Salvador <osalvador@suse.de>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    mm/page_alloc.c | 46 ++++++++++++++++++++++++++--------------------
    1 file changed, 26 insertions(+), 20 deletions(-)

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index 19f2e77d1c50b..8a00c32191263 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -6456,6 +6456,29 @@ void __init free_area_init_node(int nid, unsigned long *zones_size,
    }

    #if defined(CONFIG_HAVE_MEMBLOCK) && !defined(CONFIG_FLAT_NODE_MEM_MAP)
    +
    +/*
    + * Zero all valid struct pages in range [spfn, epfn), return number of struct
    + * pages zeroed
    + */
    +static u64 zero_pfn_range(unsigned long spfn, unsigned long epfn)
    +{
    + unsigned long pfn;
    + u64 pgcnt = 0;
    +
    + for (pfn = spfn; pfn < epfn; pfn++) {
    + if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
    + pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
    + + pageblock_nr_pages - 1;
    + continue;
    + }
    + mm_zero_struct_page(pfn_to_page(pfn));
    + pgcnt++;
    + }
    +
    + return pgcnt;
    +}
    +
    /*
    * Only struct pages that are backed by physical memory are zeroed and
    * initialized by going through __init_single_page(). But, there are some
    @@ -6471,7 +6494,6 @@ void __init free_area_init_node(int nid, unsigned long *zones_size,
    void __init zero_resv_unavail(void)
    {
    phys_addr_t start, end;
    - unsigned long pfn;
    u64 i, pgcnt;
    phys_addr_t next = 0;

    @@ -6481,34 +6503,18 @@ void __init zero_resv_unavail(void)
    pgcnt = 0;
    for_each_mem_range(i, &memblock.memory, NULL,
    NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, NULL) {
    - if (next < start) {
    - for (pfn = PFN_DOWN(next); pfn < PFN_UP(start); pfn++) {
    - if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
    - continue;
    - mm_zero_struct_page(pfn_to_page(pfn));
    - pgcnt++;
    - }
    - }
    + if (next < start)
    + pgcnt += zero_pfn_range(PFN_DOWN(next), PFN_UP(start));
    next = end;
    }
    - for (pfn = PFN_DOWN(next); pfn < max_pfn; pfn++) {
    - if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
    - continue;
    - mm_zero_struct_page(pfn_to_page(pfn));
    - pgcnt++;
    - }
    -
    + pgcnt += zero_pfn_range(PFN_DOWN(next), max_pfn);

    /*
    * Struct pages that do not have backing memory. This could be because
    * firmware is using some of this memory, or for some other reasons.
    - * Once memblock is changed so such behaviour is not allowed: i.e.
    - * list of "reserved" memory must be a subset of list of "memory", then
    - * this code can be removed.
    */
    if (pgcnt)
    pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);
    -
    }
    #endif /* CONFIG_HAVE_MEMBLOCK && !CONFIG_FLAT_NODE_MEM_MAP */

    --
    2.20.1


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