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    SubjectRe: [RFC PATCH 0/3] Add mmap(MAP_CONTIG) support
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    On 10/12/2017 04:06 PM, Anshuman Khandual wrote:
    > On 10/12/2017 07:16 AM, Mike Kravetz wrote:
    >> The following is a 'possible' way to add such functionality. I just
    >> did what was easy and pre-allocated contiguous pages which are used
    >> to populate the mapping. I did not use any of the higher order
    >> allocators such as alloc_contig_range. Therefore, it is limited to
    > Just tried with a small prototype with an implementation similar to that
    > of alloc_gigantic_page() where we scan the zones (applicable zonelist)
    > for contiguous valid PFN range and try allocating with alloc_contig_range.
    > Will share it soon.
    >

    With this patch on top of the series can allocate little more than
    twice of 1UL << (MAX_ORDER - 1) number of pages on POWER. But the
    problem is it keeps on reducing every attempt till it reaches
    1UL << (MAX_ORDER - 1). Will look into it.

    diff --git a/arch/powerpc/include/uapi/asm/mman.h b/arch/powerpc/include/uapi/asm/mman.h
    index 03c06ba..ce13b36 100644
    --- a/arch/powerpc/include/uapi/asm/mman.h
    +++ b/arch/powerpc/include/uapi/asm/mman.h
    @@ -28,5 +28,6 @@
    #define MAP_NONBLOCK 0x10000 /* do not block on IO */
    #define MAP_STACK 0x20000 /* give out an address that is best suited for process/thread stacks */
    #define MAP_HUGETLB 0x40000 /* create a huge page mapping */
    +#define MAP_CONTIG 0x80000 /* back with contiguous pages */

    #endif /* _UAPI_ASM_POWERPC_MMAN_H */
    diff --git a/mm/mmap.c b/mm/mmap.c
    index aee7917..4e6588d 100644
    --- a/mm/mmap.c
    +++ b/mm/mmap.c
    @@ -1568,6 +1568,60 @@ struct mmap_arg_struct {
    }
    #endif /* __ARCH_WANT_SYS_OLD_MMAP */

    +static bool is_pfn_range_valid(struct zone *z,
    + unsigned long start_pfn, unsigned long nr_pages)
    +{
    + unsigned long i, end_pfn = start_pfn + nr_pages;
    + struct page *page;
    +
    + for (i = start_pfn; i < end_pfn; i++) {
    + if (!pfn_valid(i))
    + return false;
    +
    + page = pfn_to_page(i);
    + if (page_zone(page) != z)
    + return false;
    +
    + if (PageReserved(page))
    + return false;
    +
    + if (page_count(page) > 0)
    + return false;
    +
    + if (PageHuge(page))
    + return false;
    + }
    + return true;
    +}
    +
    +struct page *
    +alloc_pages_vma_contig(gfp_t gfp, int order, struct vm_area_struct *vma,
    + unsigned long addr, int node, bool hugepage)
    +{
    + struct zonelist *zonelist = node_zonelist(node, gfp);
    + struct zoneref *z;
    + struct zone *zone;
    + unsigned long pfn, nr_pages, flags, ret;
    +
    + nr_pages = 1 << order;
    + for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp), NULL) {
    + spin_lock_irqsave(&zone->lock, flags);
    + pfn = ALIGN(zone->zone_start_pfn, nr_pages);
    + while (zone_spans_pfn(zone, pfn + nr_pages - 1)) {
    + if (is_pfn_range_valid(zone, pfn, nr_pages)) {
    + spin_unlock_irqrestore(&zone->lock, flags);
    + ret = alloc_contig_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE, gfp);
    + if (!ret)
    + return pfn_to_page(pfn);
    + spin_lock_irqsave(&zone->lock, flags);
    + }
    + pfn += nr_pages;
    + }
    + spin_unlock_irqrestore(&zone->lock, flags);
    + }
    + return NULL;
    +}
    +
    /*
    * Attempt to allocate a contiguous range of pages to back the
    * specified vma. vm_private_data is used as a 'pointer' to the
    @@ -1588,11 +1642,19 @@ static long __alloc_vma_contig_range(struct vm_area_struct *vma)
    * allocations < MAX_ORDER in size. However, this should really
    * handle arbitrary size allocations.
    */
    +
    + /*
    if (order >= MAX_ORDER)
    return -ENOMEM;

    - vma->vm_private_data = alloc_pages_vma(gfp, order, vma, vma->vm_start,
    - numa_node_id(), false);
    + */
    +
    + if (order >= MAX_ORDER)
    + vma->vm_private_data = alloc_pages_vma_contig(gfp, order, vma,
    + vma->vm_start, numa_node_id(), false);
    + else
    + vma->vm_private_data = alloc_pages_vma(gfp, order, vma,
    + vma->vm_start, numa_node_id(), false);
    if (!vma->vm_private_data)
    return -ENOMEM;

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