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authorHugh Dickins <hugh@veritas.com>2008-02-04 22:28:45 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-05 09:44:15 -0800
commit8952898b0d25223f38daf46b86156fd1c4d17ad0 (patch)
tree10912460cd9d42195d4aba8250ed1c3bd3577bb4 /mm/swapfile.c
parent5402b976ae0be96b3a32f3508ab7308c380d6477 (diff)
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>
Diffstat (limited to 'mm/swapfile.c')
-rw-r--r--mm/swapfile.c49
1 files changed, 33 insertions, 16 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index ab93505dfbf..f5ba723faf8 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1769,31 +1769,48 @@ get_swap_info_struct(unsigned type)
*/
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)
+ 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 (!si->swap_map[toff])
+ break;
+ if (si->swap_map[toff] == SWAP_MAP_BAD)
break;
+ }
+ /* Count contiguous allocated slots below our target */
+ for (toff = target; --toff >= base; 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);
+ }
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;
}