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    Subject[RFC PATCH 2/3] mm: add find_alloc_contig_pages() interface
    Date
    find_alloc_contig_pages() is a new interface that attempts to locate
    and allocate a contiguous range of pages. It is provided as a more
    convenient interface to the existing alloc_contig_range() interface
    which is used by CMA, memory hotplug and gigantic huge pages.

    When attempting to allocate a range of pages, migration is employed
    if possible. There is no guarantee that the routine will succeed.
    So, the user must be prepared for failure and have a fall back plan.

    Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
    ---
    include/linux/gfp.h | 12 ++++++++
    mm/page_alloc.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++--
    2 files changed, 99 insertions(+), 2 deletions(-)

    diff --git a/include/linux/gfp.h b/include/linux/gfp.h
    index 1a4582b44d32..456979022956 100644
    --- a/include/linux/gfp.h
    +++ b/include/linux/gfp.h
    @@ -573,6 +573,18 @@ static inline bool pm_suspended_storage(void)
    extern int alloc_contig_range(unsigned long start, unsigned long end,
    unsigned migratetype, gfp_t gfp_mask);
    extern void free_contig_range(unsigned long pfn, unsigned nr_pages);
    +extern struct page *find_alloc_contig_pages(unsigned int order, gfp_t gfp,
    + int nid, nodemask_t *nodemask);
    +extern void free_contig_pages(struct page *page, unsigned nr_pages);
    +#else
    +static inline page *find_alloc_contig_pages(unsigned int order, gfp_t gfp,
    + int nid, nodemask_t *nodemask)
    +{
    + return NULL;
    +}
    +static void free_contig_pages(struct page *page, unsigned nr_pages)
    +{
    +}
    #endif

    #ifdef CONFIG_CMA
    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index 064458f317bf..0a5a547acdbf 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -67,6 +67,7 @@
    #include <linux/ftrace.h>
    #include <linux/lockdep.h>
    #include <linux/nmi.h>
    +#include <linux/mmzone.h>

    #include <asm/sections.h>
    #include <asm/tlbflush.h>
    @@ -1873,9 +1874,13 @@ static __always_inline struct page *__rmqueue_cma_fallback(struct zone *zone,
    {
    return __rmqueue_smallest(zone, order, MIGRATE_CMA);
    }
    +#define contig_alloc_migratetype_ok(migratetype) \
    + ((migratetype) == MIGRATE_CMA || (migratetype) == MIGRATE_MOVABLE)
    #else
    static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
    unsigned int order) { return NULL; }
    +#define contig_alloc_migratetype_ok(migratetype) \
    + ((migratetype) == MIGRATE_MOVABLE)
    #endif

    /*
    @@ -7633,6 +7638,9 @@ int alloc_contig_range(unsigned long start, unsigned long end,
    };
    INIT_LIST_HEAD(&cc.migratepages);

    + if (!contig_alloc_migratetype_ok(migratetype))
    + return -EINVAL;
    +
    /*
    * What we do here is we mark all pageblocks in range as
    * MIGRATE_ISOLATE. Because pageblock and max order pages may
    @@ -7723,8 +7731,9 @@ int alloc_contig_range(unsigned long start, unsigned long end,

    /* Make sure the range is really isolated. */
    if (test_pages_isolated(outer_start, end, false)) {
    - pr_info_ratelimited("%s: [%lx, %lx) PFNs busy\n",
    - __func__, outer_start, end);
    + if (!(migratetype == MIGRATE_MOVABLE)) /* only print for CMA */
    + pr_info_ratelimited("%s: [%lx, %lx) PFNs busy\n",
    + __func__, outer_start, end);
    ret = -EBUSY;
    goto done;
    }
    @@ -7760,6 +7769,82 @@ void free_contig_range(unsigned long pfn, unsigned nr_pages)
    }
    WARN(count != 0, "%d pages are still in use!\n", count);
    }
    +
    +static bool contig_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;
    +
    + }
    +
    + return true;
    +}
    +
    +/**
    + * find_alloc_contig_pages() -- attempt to find and allocate a contiguous
    + * range of pages
    + * @order: number of pages
    + * @gfp: gfp mask used to limit search as well as during compaction
    + * @nid: target node
    + * @nodemask: mask of other possible nodes
    + *
    + * Returns pointer to 'order' pages on success, or NULL if not successful.
    + *
    + * Pages can be freed with a call to free_contig_pages(), or by manually
    + * calling __free_page() for each page allocated.
    + */
    +struct page *find_alloc_contig_pages(unsigned int order, gfp_t gfp,
    + int nid, nodemask_t *nodemask)
    +{
    + unsigned long pfn, nr_pages, flags;
    + struct page *ret_page = NULL;
    + struct zonelist *zonelist;
    + struct zoneref *z;
    + struct zone *zone;
    + int rc;
    +
    + nr_pages = 1 << order;
    + zonelist = node_zonelist(nid, gfp);
    + for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp),
    + nodemask) {
    + spin_lock_irqsave(&zone->lock, flags);
    + pfn = ALIGN(zone->zone_start_pfn, nr_pages);
    + while (zone_spans_pfn(zone, pfn + nr_pages - 1)) {
    + if (contig_pfn_range_valid(zone, pfn, nr_pages)) {
    + spin_unlock_irqrestore(&zone->lock, flags);
    +
    + rc = alloc_contig_range(pfn, pfn + nr_pages,
    + MIGRATE_MOVABLE, gfp);
    + if (!rc) {
    + ret_page = pfn_to_page(pfn);
    + return ret_page;
    + }
    + spin_lock_irqsave(&zone->lock, flags);
    + }
    + pfn += nr_pages;
    + }
    + spin_unlock_irqrestore(&zone->lock, flags);
    + }
    +
    + return ret_page;
    +}
    +EXPORT_SYMBOL_GPL(find_alloc_contig_pages);
    +
    +void free_contig_pages(struct page *page, unsigned nr_pages)
    +{
    + free_contig_range(page_to_pfn(page), nr_pages);
    +}
    +EXPORT_SYMBOL_GPL(free_contig_pages);
    #endif

    #ifdef CONFIG_MEMORY_HOTPLUG
    --
    2.13.6
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