swapin: fix valid_swaphandles defect
valid_swaphandles is supposed to do a quick pass over the swap map entries
neigbouring the entry which swapin_readahead is targetting, to determine for
it a range worth reading all together. But since it always starts its search
from the beginning of the swap "cluster", a reject (free entry) there
immediately curtails the readaround, and every swapin_readahead from that
cluster is for just a single page. Instead scan forwards and backwards around
the target entry.
Use better names for some variables: a swap_info pointer is usually called
"si" not "swapdev". And at the end, if only the target page should be read,
return count of 0 to disable readaround, to avoid the unnecessarily repeated
call to read_swap_cache_async.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/swapfile.c b/mm/swapfile.c
index ab93505..f5ba723 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1769,31 +1769,48 @@
*/
int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
{
+ struct swap_info_struct *si;
int our_page_cluster = page_cluster;
- int ret = 0, i = 1 << our_page_cluster;
- unsigned long toff;
- struct swap_info_struct *swapdev = swp_type(entry) + swap_info;
+ pgoff_t target, toff;
+ pgoff_t base, end;
+ int nr_pages = 0;
if (!our_page_cluster) /* no readahead */
return 0;
- toff = (swp_offset(entry) >> our_page_cluster) << our_page_cluster;
- if (!toff) /* first page is swap header */
- toff++, i--;
- *offset = toff;
+
+ si = &swap_info[swp_type(entry)];
+ target = swp_offset(entry);
+ base = (target >> our_page_cluster) << our_page_cluster;
+ end = base + (1 << our_page_cluster);
+ if (!base) /* first page is swap header */
+ base++;
spin_lock(&swap_lock);
- do {
- /* Don't read-ahead past the end of the swap area */
- if (toff >= swapdev->max)
- break;
+ if (end > si->max) /* don't go beyond end of map */
+ end = si->max;
+
+ /* Count contiguous allocated slots above our target */
+ for (toff = target; ++toff < end; nr_pages++) {
/* Don't read in free or bad pages */
- if (!swapdev->swap_map[toff])
+ if (!si->swap_map[toff])
break;
- if (swapdev->swap_map[toff] == SWAP_MAP_BAD)
+ if (si->swap_map[toff] == SWAP_MAP_BAD)
break;
- toff++;
- ret++;
- } while (--i);
+ }
+ /* Count contiguous allocated slots below our target */
+ for (toff = target; --toff >= base; nr_pages++) {
+ /* Don't read in free or bad pages */
+ if (!si->swap_map[toff])
+ break;
+ if (si->swap_map[toff] == SWAP_MAP_BAD)
+ break;
+ }
spin_unlock(&swap_lock);
- return ret;
+
+ /*
+ * Indicate starting offset, and return number of pages to get:
+ * if only 1, say 0, since there's then no readahead to be done.
+ */
+ *offset = ++toff;
+ return nr_pages? ++nr_pages: 0;
}