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DateWed, 27 May 2009 14:14:42 +0900
FromKAMEZAWA Hiroyuki <>
SubjectRe: [RFC][PATCH 5/5] (experimental) chase and free cache only swap
On Tue, 26 May 2009 12:18:34 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

>
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
This is a replacement for this. (just an idea, not testd.)

I think this works well. Does anyone has concerns ?
Do I have to modify swap-cluster code to do this in sane way ?

---
mm/swapfile.c | 40 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)
Index: new-trial-swapcount/mm/swapfile.c
===================================================================
--- new-trial-swapcount.orig/mm/swapfile.c
+++ new-trial-swapcount/mm/swapfile.c
@@ -74,6 +74,26 @@ static inline unsigned short make_swap_c
return ret;
}

+static int try_to_reuse_swap(struct swap_info_struct *si, unsigned long offset)
+{
+ int type = si - swap_info;
+ swp_entry_t entry = swp_entry(type, offset);
+ struct page *page;
+
+ page = find_get_page(page);
+ if (!page)
+ return 0;
+ if (!trylock_page(page)) {
+ page_cache_release(page);
+ return 0;
+ }
+ try_to_free_swap(page);
+ unlock_page(page);
+ page_cache_release(page);
+ return 1;
+}
+
+
/*
* We need this because the bdev->unplug_fn can sleep and we cannot
* hold swap_lock while calling the unplug_fn. And swap_lock
@@ -295,6 +315,18 @@ checks:
goto no_page;
if (offset > si->highest_bit)
scan_base = offset = si->lowest_bit;
+
+ /* reuse swap entry of cache-only swap if not busy. */
+ if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
+ int ret;
+ spin_unlock(&swap_lock);
+ ret = try_to_reuse_swap(si, offset));
+ spin_lock(&swap_lock);
+ if (ret)
+ goto checks; /* we released swap_lock */
+ goto scan;
+ }
+
if (si->swap_map[offset])
goto scan;

@@ -378,6 +410,10 @@ scan:
spin_lock(&swap_lock);
goto checks;
}
+ if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
+ spin_lock(&swap_lock);
+ goto checks;
+ }
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
@@ -389,6 +425,10 @@ scan:
spin_lock(&swap_lock);
goto checks;
}
+ if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
+ spin_lock(&swap_lock);
+ goto checks;
+ }
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;


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