heart of memoy allocation: __alloc_pages()

 

static inline struct page *
__alloc_pages(gfp_t gfp_mask, unsigned int order,
        struct zonelist *zonelist)
{
    return __alloc_pages_nodemask(gfp_mask, order, zonelist, NULL);
}

---


/*
 * This is the 'heart' of the zoned buddy allocator.
 */
struct page *
__alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
            struct zonelist *zonelist, nodemask_t *nodemask)
{

    //get zone type using gfp_mask
    enum zone_type high_zoneidx = gfp_zone(gfp_mask);
    struct zone *preferred_zone;
    struct page *page;

    //see comment 1
    int migratetype = allocflags_to_migratetype(gfp_mask);

    gfp_mask &= gfp_allowed_mask;

    lockdep_trace_alloc(gfp_mask);

    might_sleep_if(gfp_mask & __GFP_WAIT);

    if (should_fail_alloc_page(gfp_mask, order))
        return NULL;

    /*
     * Check the zones suitable for the gfp_mask contain at least one
     * valid zone. It's possible to have an empty zonelist as a result
     * of GFP_THISNODE and a memoryless node
     */
    if (unlikely(!zonelist->_zonerefs->zone))
        return NULL;

    get_mems_allowed();
    /* The preferred zone is used for statistics later */
    first_zones_zonelist(zonelist, high_zoneidx, nodemask, &preferred_zone);
    if (!preferred_zone) {
        put_mems_allowed();
        return NULL;
    }

    /* First allocation attempt */
    page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
            zonelist, high_zoneidx, ALLOC_WMARK_LOW|ALLOC_CPUSET,
            preferred_zone, migratetype);
    if (unlikely(!page))
        page = __alloc_pages_slowpath(gfp_mask, order,
                zonelist, high_zoneidx, nodemask,
                preferred_zone, migratetype);
    put_mems_allowed();

    trace_mm_page_alloc(page, order, gfp_mask, migratetype);
    return page;
}
EXPORT_SYMBOL(__alloc_pages_nodemask);

---

Comment 1:
Convert GFP flags to their corresponding migrate type. What is migrate type?
in mmzone.h:

#define MIGRATE_UNMOVABLE     0
#define MIGRATE_RECLAIMABLE   1
#define MIGRATE_MOVABLE       2
#define MIGRATE_PCPTYPES      3 /* the number of types on the pcp lists */
#define MIGRATE_RESERVE       3
#define MIGRATE_ISOLATE       4 /* can't allocate from here */
#define MIGRATE_TYPES         5

#define for_each_migratetype_order(order, type) \
    for (order = 0; order < MAX_ORDER; order++) \
        for (type = 0; type < MIGRATE_TYPES; type++)

migrate type is used to specify the index of freelist[] in struct free_area.
struct free_area {
    struct list_head    free_list[MIGRATE_TYPES];
    unsigned long        nr_free;
};

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