[PATCH] Caches that shrink automatically

[Andreas Gruenbacher <agruen@suse.de>]

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Hello,

Currently there is no way for modules to define dynamically sized caches that 
shrink upon memory pressure. We need this for implementing Extended Attribute 
caches on ext2, ext3, and ReiserFS. Other caches could also make use of the 
same mechanism (e.g., nfsd's permission cache, dcache, icache, dqache).

I propose this patch, which adds the register_cache() and unregister_cache() 
functions. They allow to register a callback which is invoked on memory 
pressure. This callback shall then try to free some memory; the parameters 
and semantics are similar to the other shrink functions in mm/vmscan.c.


Regards,
Andreas.

------------------------------------------------------------------
 Andreas Gruenbacher                                SuSE Linux AG
 mailto:agruen@suse.de                     Deutschherrnstr. 15-19
 http://www.suse.de/                   D-90429 Nuernberg, Germany

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Modular caches that shrink automatically

This patch adds the register_cache() and unregister_cache() functions which
register a callback that is invoked on memory pressure to free some memory. The
parameters and semantics to the callback are similar to the other shrink
functions.

diff -Nur linux-2.5.30/include/linux/cache_def.h linux-2.5.30.patch/include/linux/cache_def.h
--- linux-2.5.30/include/linux/cache_def.h	Thu Jan  1 01:00:00 1970
+++ linux-2.5.30.patch/include/linux/cache_def.h	Sat Aug  3 13:58:07 2002
@@ -0,0 +1,15 @@
+/*
+ * linux/cache_def.h
+ * Modular caches that shrink automatically
+ *
+ * Copyright (C) 2002 by Andreas Gruenbacher, <a.gruenbacher@computer.org>
+ */
+
+struct cache_definition {
+	const char *name;
+	void (*shrink)(int, unsigned int);
+	struct list_head link;
+};
+
+extern void register_cache(struct cache_definition *);
+extern void unregister_cache(struct cache_definition *);
diff -Nur linux-2.5.30/kernel/ksyms.c linux-2.5.30.patch/kernel/ksyms.c
--- linux-2.5.30/kernel/ksyms.c	Thu Aug  1 23:16:02 2002
+++ linux-2.5.30.patch/kernel/ksyms.c	Fri Aug  2 15:57:42 2002
@@ -31,6 +31,7 @@
 #include <linux/genhd.h>
 #include <linux/blkpg.h>
 #include <linux/swap.h>
+#include <linux/cache_def.h>
 #include <linux/ctype.h>
 #include <linux/file.h>
 #include <linux/iobuf.h>
@@ -106,6 +107,8 @@
 EXPORT_SYMBOL(kmem_cache_alloc);
 EXPORT_SYMBOL(kmem_cache_free);
 EXPORT_SYMBOL(kmem_cache_size);
+EXPORT_SYMBOL(register_cache);
+EXPORT_SYMBOL(unregister_cache);
 EXPORT_SYMBOL(kmalloc);
 EXPORT_SYMBOL(kfree);
 EXPORT_SYMBOL(vfree);
Binary files linux-2.5.30/mm/.vmscan.c.swp and linux-2.5.30.patch/mm/.vmscan.c.swp differ
diff -Nur linux-2.5.30/mm/vmscan.c linux-2.5.30.patch/mm/vmscan.c
--- linux-2.5.30/mm/vmscan.c	Thu Aug  1 23:16:08 2002
+++ linux-2.5.30.patch/mm/vmscan.c	Sat Aug  3 13:56:55 2002
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/kernel_stat.h>
 #include <linux/swap.h>
+#include <linux/cache_def.h>
 #include <linux/smp_lock.h>
 #include <linux/pagemap.h>
 #include <linux/init.h>
@@ -61,6 +62,39 @@
 	return 0;
 }
 
+static DECLARE_MUTEX(other_caches_lock);
+static LIST_HEAD(other_caches);
+
+void register_cache(struct cache_definition *cache)
+{
+	down(&other_caches_lock);
+	list_add(&cache->link, &other_caches);
+	up(&other_caches_lock);
+}
+
+void unregister_cache(struct cache_definition *cache)
+{
+	down(&other_caches_lock);
+	list_del(&cache->link);
+	up(&other_caches_lock);
+}
+
+static void shrink_other_caches(unsigned int priority, int gfp_mask)
+{
+	struct list_head *p = other_caches.prev;
+
+	down(&other_caches_lock);
+	while (p != &other_caches) {
+		struct cache_definition *cache =
+			list_entry(p, struct cache_definition, link);
+
+		cache->shrink(priority, gfp_mask);
+		p = p->prev;
+	}
+	up(&other_caches_lock);
+}
+
+
 static int
 shrink_cache(int nr_pages, zone_t *classzone,
 		unsigned int gfp_mask, int priority, int max_scan)
@@ -395,6 +429,7 @@
 #ifdef CONFIG_QUOTA
 	shrink_dqcache_memory(DEF_PRIORITY, gfp_mask);
 #endif
+	shrink_other_caches(priority, gfp_mask);
 
 	return nr_pages;
 }