From: Hugh Dickins Date: Sat, 3 Sep 2005 22:54:38 +0000 (-0700) Subject: [PATCH] swap: scan_swap_map restyled X-Git-Tag: v2.6.14-rc1~981 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=7dfad4183bf9cd92f977caa3c12cc74f0eefc0e6;p=linux-2.6-omap-h63xx.git [PATCH] swap: scan_swap_map restyled Rewrite scan_swap_map to allocate in just the same way as before (taking the next free entry SWAPFILE_CLUSTER-1 times, then restarting at the lowest wholly empty cluster, falling back to lowest entry if none), but with a view towards dropping the lock in the next patch. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/swapfile.c b/mm/swapfile.c index e54d60af6b5..c70248aab53 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -86,64 +86,67 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page) static inline unsigned long scan_swap_map(struct swap_info_struct *si) { - unsigned long offset; + unsigned long offset, last_in_cluster; + /* - * We try to cluster swap pages by allocating them - * sequentially in swap. Once we've allocated - * SWAPFILE_CLUSTER pages this way, however, we resort to - * first-free allocation, starting a new cluster. This - * prevents us from scattering swap pages all over the entire - * swap partition, so that we reduce overall disk seek times - * between swap pages. -- sct */ - if (si->cluster_nr) { - while (si->cluster_next <= si->highest_bit) { - offset = si->cluster_next++; + * We try to cluster swap pages by allocating them sequentially + * in swap. Once we've allocated SWAPFILE_CLUSTER pages this + * way, however, we resort to first-free allocation, starting + * a new cluster. This prevents us from scattering swap pages + * all over the entire swap partition, so that we reduce + * overall disk seek times between swap pages. -- sct + * But we do now try to find an empty cluster. -Andrea + */ + + if (unlikely(!si->cluster_nr)) { + si->cluster_nr = SWAPFILE_CLUSTER - 1; + if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) + goto lowest; + + offset = si->lowest_bit; + last_in_cluster = offset + SWAPFILE_CLUSTER - 1; + + /* Locate the first empty (unaligned) cluster */ + for (; last_in_cluster <= si->highest_bit; offset++) { if (si->swap_map[offset]) - continue; - si->cluster_nr--; - goto got_page; - } - } - si->cluster_nr = SWAPFILE_CLUSTER; - - /* try to find an empty (even not aligned) cluster. */ - offset = si->lowest_bit; - check_next_cluster: - if (offset+SWAPFILE_CLUSTER-1 <= si->highest_bit) - { - unsigned long nr; - for (nr = offset; nr < offset+SWAPFILE_CLUSTER; nr++) - if (si->swap_map[nr]) - { - offset = nr+1; - goto check_next_cluster; + last_in_cluster = offset + SWAPFILE_CLUSTER; + else if (offset == last_in_cluster) { + si->cluster_next = offset-SWAPFILE_CLUSTER-1; + goto cluster; } - /* We found a completly empty cluster, so start - * using it. - */ - goto got_page; + } + goto lowest; } - /* No luck, so now go finegrined as usual. -Andrea */ - for (offset = si->lowest_bit; offset <= si->highest_bit ; offset++) { - if (si->swap_map[offset]) - continue; - si->lowest_bit = offset+1; - got_page: - if (offset == si->lowest_bit) + + si->cluster_nr--; +cluster: + offset = si->cluster_next; + if (offset > si->highest_bit) +lowest: offset = si->lowest_bit; + if (!si->highest_bit) + goto no_page; + if (!si->swap_map[offset]) { +got_page: if (offset == si->lowest_bit) si->lowest_bit++; if (offset == si->highest_bit) si->highest_bit--; - if (si->lowest_bit > si->highest_bit) { + si->inuse_pages++; + if (si->inuse_pages == si->pages) { si->lowest_bit = si->max; si->highest_bit = 0; } si->swap_map[offset] = 1; - si->inuse_pages++; - si->cluster_next = offset+1; + si->cluster_next = offset + 1; return offset; } - si->lowest_bit = si->max; - si->highest_bit = 0; + + while (++offset <= si->highest_bit) { + if (!si->swap_map[offset]) + goto got_page; + } + goto lowest; + +no_page: return 0; }