1 files changed, 60 insertions, 3 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 98e85e9c2b2d..e76ace30d436 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -63,6 +63,8 @@ unsigned long total_swapcache_pages(void)
         return ret;
 }
 
+static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
+
 void show_swap_cache_info(void)
 {
         printk("%lu pages in swap cache\n", total_swapcache_pages());
@@ -286,8 +288,11 @@ struct page * lookup_swap_cache(swp_entry_t entry)
 
         page = find_get_page(swap_address_space(entry), entry.val);
 
-        if (page)
+        if (page) {
                 INC_CACHE_INFO(find_success);
+                if (TestClearPageReadahead(page))
+                        atomic_inc(&swapin_readahead_hits);
+        }
 
         INC_CACHE_INFO(find_total);
         return page;
@@ -389,6 +394,50 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
         return found_page;
 }
 
+static unsigned long swapin_nr_pages(unsigned long offset)
+{
+        static unsigned long prev_offset;
+        unsigned int pages, max_pages, last_ra;
+        static atomic_t last_readahead_pages;
+
+        max_pages = 1 << ACCESS_ONCE(page_cluster);
+        if (max_pages <= 1)
+                return 1;
+
+        /*
+         * This heuristic has been found to work well on both sequential and
+         * random loads, swapping to hard disk or to SSD: please don't ask
+         * what the "+ 2" means, it just happens to work well, that's all.
+         */
+        pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
+        if (pages == 2) {
+                /*
+                 * We can have no readahead hits to judge by: but must not get
+                 * stuck here forever, so check for an adjacent offset instead
+                 * (and don't even bother to check whether swap type is same).
+                 */
+                if (offset != prev_offset + 1 && offset != prev_offset - 1)
+                        pages = 1;
+                prev_offset = offset;
+        } else {
+                unsigned int roundup = 4;
+                while (roundup < pages)
+                        roundup <<= 1;
+                pages = roundup;
+        }
+
+        if (pages > max_pages)
+                pages = max_pages;
+
+        /* Don't shrink readahead too fast */
+        last_ra = atomic_read(&last_readahead_pages) / 2;
+        if (pages < last_ra)
+                pages = last_ra;
+        atomic_set(&last_readahead_pages, pages);
+
+        return pages;
+}
+
 /**
  * swapin_readahead - swap in pages in hope we need them soon
  * @entry: swap entry of this memory
@@ -412,11 +461,16 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
                         struct vm_area_struct *vma, unsigned long addr)
 {
         struct page *page;
-        unsigned long offset = swp_offset(entry);
+        unsigned long entry_offset = swp_offset(entry);
+        unsigned long offset = entry_offset;
         unsigned long start_offset, end_offset;
-        unsigned long mask = (1UL << page_cluster) - 1;
+        unsigned long mask;
         struct blk_plug plug;
 
+        mask = swapin_nr_pages(offset) - 1;
+        if (!mask)
+                goto skip;
+
         /* Read a page_cluster sized and aligned cluster around offset. */
         start_offset = offset & ~mask;
         end_offset = offset | mask;
@@ -430,10 +484,13 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
                                                 gfp_mask, vma, addr);
                 if (!page)
                         continue;
+                if (offset != entry_offset)
+                        SetPageReadahead(page);
                 page_cache_release(page);
         }
         blk_finish_plug(&plug);
 
         lru_add_drain();        /* Push any new pages onto the LRU now */
+skip:
         return read_swap_cache_async(entry, gfp_mask, vma, addr);
 }