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Message-Id: <20090526121834.dd9a4193.kamezawa.hiroyu@jp.fujitsu.com>
Date: Tue, 26 May 2009 12:18:34 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
"hannes@...xchg.org" <hannes@...xchg.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [RFC][PATCH 5/5] (experimental) chase and free cache only swap
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Just a trial/example patch.
I'd like to consider more. Better implementation idea is welcome.
When the system does swap-in/swap-out repeatedly, there are
cache-only swaps in general.
Typically,
- swapped out in past but on memory now while vm_swap_full() returns true
pages are cache-only swaps. (swap_map has no references.)
This cache-only swaps can be an obstacles for smooth page reclaiming.
Current implemantation is very naive, just scan & free.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
include/linux/swap.h | 1
mm/swapfile.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 89 insertions(+)
Index: new-trial-swapcount/mm/swapfile.c
===================================================================
--- new-trial-swapcount.orig/mm/swapfile.c
+++ new-trial-swapcount/mm/swapfile.c
@@ -74,6 +74,8 @@ static inline unsigned short make_swap_c
return ret;
}
+static void call_gc_cache_only_swap(void);
+
/*
* We need this because the bdev->unplug_fn can sleep and we cannot
* hold swap_lock while calling the unplug_fn. And swap_lock
@@ -432,6 +434,8 @@ swp_entry_t get_swap_page(void)
offset = scan_swap_map(si, 1);
if (offset) {
spin_unlock(&swap_lock);
+ /* reclaim cache-only swaps if vm_swap_full() */
+ call_gc_cache_only_swap();
return swp_entry(type, offset);
}
next = swap_list.next;
@@ -2147,3 +2151,87 @@ int valid_swaphandles(swp_entry_t entry,
*offset = ++toff;
return nr_pages? ++nr_pages: 0;
}
+
+/*
+ * Following code is for freeing Cache-only swap entries. These are calle in
+ * vm_swap_full() situation, and freeing cache-only swap and make some swap
+ * entries usable.
+ */
+
+static int find_free_cache_only_swap(int type)
+{
+ unsigned long buf[SWAP_CLUSTER_MAX];
+ int nr, offset, i;
+ unsigned short count;
+ struct swap_info_struct *si = swap_info + type;
+ int ret = 0;
+
+ spin_lock(&swap_lock);
+ nr = 0;
+ if (!(si->flags & SWP_WRITEOK) || si->cache_only == 0) {
+ ret = 1;
+ goto unlock;
+ }
+ offset = si->garbage_scan_offset;
+ /* Scan 2048 entries at most and free up to 32 entries per scan.*/
+ for (i = 2048; i > 0 && nr < 32; i--, offset++) {
+ if (offset >= si->max) {
+ offset = 0;
+ ret = 1;
+ break;
+ }
+ count = si->swap_map[offset];
+ if (count == SWAP_HAS_CACHE)
+ buf[nr++] = offset;
+ }
+ si->garbage_scan_offset = offset;
+unlock:
+ spin_unlock(&swap_lock);
+
+ for (i = 0; i < nr; i++) {
+ swp_entry_t ent;
+ struct page *page;
+
+ ent = swp_entry(type, buf[i]);
+
+ page = find_get_page(&swapper_space, ent.val);
+ if (page) {
+ lock_page(page);
+ try_to_free_swap(page);
+ unlock_page(page);
+ }
+ }
+ return ret;
+}
+
+#define SWAP_GC_THRESH (4096)
+static void scan_and_free_cache_only_swap_work(struct work_struct *work);
+DECLARE_DELAYED_WORK(swap_gc_work, scan_and_free_cache_only_swap_work);
+static int swap_gc_last_scan;
+
+static void scan_and_free_cache_only_swap_work(struct work_struct *work)
+{
+ int type = swap_gc_last_scan;
+ int i;
+
+ spin_lock(&swap_lock);
+ for (i = type; i < MAX_SWAPFILES; i++) {
+ if (swap_info[i].flags & SWP_WRITEOK)
+ break;
+ }
+ if (i >= MAX_SWAPFILES)
+ i = 0;
+ spin_unlock(&swap_lock);
+ if (find_free_cache_only_swap(i))
+ swap_gc_last_scan = i + 1;
+
+ if (vm_swap_full() && (nr_cache_only_swaps > SWAP_GC_THRESH))
+ schedule_delayed_work(&swap_gc_work, HZ/10);
+}
+
+static void call_gc_cache_only_swap(void)
+{
+ if (vm_swap_full() && (nr_cache_only_swaps > SWAP_GC_THRESH))
+ schedule_delayed_work(&swap_gc_work, HZ/10);
+}
+
Index: new-trial-swapcount/include/linux/swap.h
===================================================================
--- new-trial-swapcount.orig/include/linux/swap.h
+++ new-trial-swapcount/include/linux/swap.h
@@ -156,6 +156,7 @@ struct swap_info_struct {
unsigned int inuse_pages;
unsigned int old_block_size;
unsigned int cache_only;
+ unsigned int garbage_scan_offset;
};
struct swap_list_t {
--
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