linux-kernel - Re: [RFC][PATCH 5/5] (experimental) chase and free cache only swap

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Date:	Wed, 27 May 2009 14:14:42 +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: Re: [RFC][PATCH 5/5] (experimental) chase and free cache only swap

On Tue, 26 May 2009 12:18:34 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> 
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...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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