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-rw-r--r--mm/swap_state.c63
1 files changed, 60 insertions, 3 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 98e85e9..e76ace3 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);
}
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