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Subject[PATCH] dcache 2nd chance replacement
Hi,

I rediffed this trivial patch by Andrea (that went
into 2.2.19-pre5) which adds 2nd chance replacement
to the dentry cache, this should make our dcache
behave a little bit better than the current FIFO.

I know this probably isn't of any help under very low
and very high loads, but it should provide a nice
improvement under medium loads...

regards,

Rik
--
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Trailer at 11.

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--- linux-2.4.0-prerelease/include/linux/dcache.h.orig Wed Jan 3 16:33:43 2001
+++ linux-2.4.0-prerelease/include/linux/dcache.h Wed Jan 3 16:43:29 2001
@@ -115,6 +115,7 @@
* If this dentry points to a directory, then
* s_nfsd_free_path semaphore will be down
*/
+#define DCACHE_REFERENCED 0x0008 /* Recently used, don't discard. */

extern spinlock_t dcache_lock;

--- linux-2.4.0-prerelease/fs/dcache.c.orig Wed Jan 3 16:33:09 2001
+++ linux-2.4.0-prerelease/fs/dcache.c Wed Jan 3 16:43:10 2001
@@ -339,10 +339,18 @@

if (tmp == &dentry_unused)
break;
- dentry_stat.nr_unused--;
list_del_init(tmp);
dentry = list_entry(tmp, struct dentry, d_lru);

+ /* If the dentry was recently referenced, don't free it. */
+ if (dentry->d_flags & DCACHE_REFERENCED) {
+ dentry->d_flags &= ~DCACHE_REFERENCED;
+ list_add(&dentry->d_lru, &dentry_unused);
+ count--;
+ continue;
+ }
+ dentry_stat.nr_unused--;
+
/* Unused dentry with a count? */
if (atomic_read(&dentry->d_count))
BUG();
@@ -733,6 +741,7 @@
}
__dget_locked(dentry);
spin_unlock(&dcache_lock);
+ dentry->d_flags |= DCACHE_REFERENCED;
return dentry;
}
spin_unlock(&dcache_lock);
-
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