From c60aa176c6de82703f064082b909496fc4fee956 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 6 Jan 2009 14:39:55 -0800 Subject: [PATCH] swapfile: swap allocation cycle if nonrot Though attempting to find free clusters (Andrea), swap allocation has always restarted its searches from the beginning of the swap area (sct), to reduce seek times between swap pages, by not scattering them all over the partition. But on a solidstate swap device, seeks are cheap, and block remapping to level the wear may be limited by zones: in that case it's better to cycle around the whole partition. Signed-off-by: Hugh Dickins Cc: KAMEZAWA Hiroyuki Cc: Nick Piggin Cc: David Woodhouse Cc: Jens Axboe Cc: Matthew Wilcox Cc: Joern Engel Cc: James Bottomley Cc: Donjun Shin Cc: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swapfile.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 46 insertions(+), 4 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index b0f56603b9be..763210732b5f 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -169,6 +169,7 @@ static int wait_for_discard(void *word) static inline unsigned long scan_swap_map(struct swap_info_struct *si) { unsigned long offset; + unsigned long scan_base; unsigned long last_in_cluster = 0; int latency_ration = LATENCY_LIMIT; int found_free_cluster = 0; @@ -181,10 +182,11 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si) * 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 + * And we let swap pages go all over an SSD partition. Hugh */ si->flags += SWP_SCANNING; - offset = si->cluster_next; + scan_base = offset = si->cluster_next; if (unlikely(!si->cluster_nr--)) { if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) { @@ -206,7 +208,16 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si) } spin_unlock(&swap_lock); - offset = si->lowest_bit; + /* + * If seek is expensive, start searching for new cluster from + * start of partition, to minimize the span of allocated swap. + * But if seek is cheap, search from our current position, so + * that swap is allocated from all over the partition: if the + * Flash Translation Layer only remaps within limited zones, + * we don't want to wear out the first zone too quickly. + */ + if (!(si->flags & SWP_SOLIDSTATE)) + scan_base = offset = si->lowest_bit; last_in_cluster = offset + SWAPFILE_CLUSTER - 1; /* Locate the first empty (unaligned) cluster */ @@ -228,6 +239,27 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si) } offset = si->lowest_bit; + last_in_cluster = offset + SWAPFILE_CLUSTER - 1; + + /* Locate the first empty (unaligned) cluster */ + for (; last_in_cluster < scan_base; offset++) { + if (si->swap_map[offset]) + last_in_cluster = offset + SWAPFILE_CLUSTER; + else if (offset == last_in_cluster) { + spin_lock(&swap_lock); + offset -= SWAPFILE_CLUSTER - 1; + si->cluster_next = offset; + si->cluster_nr = SWAPFILE_CLUSTER - 1; + found_free_cluster = 1; + goto checks; + } + if (unlikely(--latency_ration < 0)) { + cond_resched(); + latency_ration = LATENCY_LIMIT; + } + } + + offset = scan_base; spin_lock(&swap_lock); si->cluster_nr = SWAPFILE_CLUSTER - 1; si->lowest_alloc = 0; @@ -239,7 +271,7 @@ checks: if (!si->highest_bit) goto no_page; if (offset > si->highest_bit) - offset = si->lowest_bit; + scan_base = offset = si->lowest_bit; if (si->swap_map[offset]) goto scan; @@ -323,8 +355,18 @@ scan: latency_ration = LATENCY_LIMIT; } } + offset = si->lowest_bit; + while (++offset < scan_base) { + if (!si->swap_map[offset]) { + spin_lock(&swap_lock); + goto checks; + } + if (unlikely(--latency_ration < 0)) { + cond_resched(); + latency_ration = LATENCY_LIMIT; + } + } spin_lock(&swap_lock); - goto checks; no_page: si->flags -= SWP_SCANNING; -- 2.20.1