Re: A couple of 2.4.23-pre4 VM nits

[Shantanu Goel <sgoel01@yahoo.com>]

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I just realized the original code had one desirable
behaviour that my patch is missing, namely, it
reclaimed memory from dcache/inode every time swap_out
is called.  Please use the attached patch that
restores the original behaviour.  Otherwise, if the
interval is very long, no reclamation will happen
until swap_out() fails which in the common case is
unlikely.

Thanks,
Shantanu

--- Andrea Arcangeli <andrea@suse.de> wrote:
> On Sat, Sep 20, 2003 at 10:32:09PM -0700, Shantanu
> Goel wrote:
> > Agreed on all counts.  I just blindly copied the
> > max_scan decrement from 2.4.22.  Even there your
> > suggestion would make sense.  Attached is a new
> patch
> > which adds support for vm_vfs_scan_interval sysctl
> and
> > also fixes the location of max_scan decrement.
> 
> this patch looks fine to me thanks. Marcelo, feel
> free to merge this one
> instead of my one liner fix.
> 
> Andrea - If you prefer relying on open source
> software, check these links:
> 	   
>
rsync.kernel.org::pub/scm/linux/kernel/bkcvs/linux-2.[45]/
> 	    http://www.cobite.com/cvsps/
> 	    svn://svn.kernel.org/linux-2.[46]/trunk

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[-- Attachment #2: vfs-interval2.patch --]
[-- Type: application/octet-stream, Size: 4032 bytes --]

--- ./kernel/sysctl.c.~1~	2003-09-16 20:44:14.000000000 -0400
+++ ./kernel/sysctl.c	2003-09-21 00:49:32.000000000 -0400
@@ -281,6 +281,8 @@
 	 &vm_gfp_debug, sizeof(int), 0644, NULL, &proc_dointvec},
 	{VM_VFS_SCAN_RATIO, "vm_vfs_scan_ratio", 
 	 &vm_vfs_scan_ratio, sizeof(int), 0644, NULL, &proc_dointvec},
+	{VM_VFS_SCAN_INTERVAL, "vm_vfs_scan_interval", 
+	 &vm_vfs_scan_interval, sizeof(int), 0644, NULL, &proc_dointvec},
 	{VM_CACHE_SCAN_RATIO, "vm_cache_scan_ratio", 
 	 &vm_cache_scan_ratio, sizeof(int), 0644, NULL, &proc_dointvec},
 	{VM_MAPPED_RATIO, "vm_mapped_ratio", 
--- ./mm/vmscan.c.~1~	2003-09-16 20:44:14.000000000 -0400
+++ ./mm/vmscan.c	2003-09-21 02:47:49.000000000 -0400
@@ -65,6 +65,12 @@
 int vm_vfs_scan_ratio = 6;
 
 /*
+ * "vm_vfs_scan_interval" is how often (in seconds)
+ * memory gets reclaimed from inode/dentry cache.
+ */
+int vm_vfs_scan_interval = MAX_SCHEDULE_TIMEOUT / HZ;
+
+/*
  * The swap-out function returns 1 if it successfully
  * scanned all the pages it was asked to (`count').
  * It returns zero if it couldn't do anything,
@@ -364,6 +370,20 @@
 	return 0;
 }
 
+static void shrink_vfs_caches(int force, unsigned int gfp_mask)
+{
+	static unsigned long last_scan = 0;
+
+	if (force || time_after(jiffies, last_scan + vm_vfs_scan_interval * HZ)) {
+		shrink_dcache_memory(vm_vfs_scan_ratio, gfp_mask);
+		shrink_icache_memory(vm_vfs_scan_ratio, gfp_mask);
+#ifdef CONFIG_QUOTA
+		shrink_dqcache_memory(vm_vfs_scan_ratio, gfp_mask);
+#endif
+		last_scan = jiffies;
+	}
+}
+
 static void FASTCALL(refill_inactive(int nr_pages, zone_t * classzone));
 static int FASTCALL(shrink_cache(int nr_pages, zone_t * classzone, unsigned int gfp_mask, int * failed_swapout));
 static int shrink_cache(int nr_pages, zone_t * classzone, unsigned int gfp_mask, int * failed_swapout)
@@ -401,6 +421,8 @@
 		if (!memclass(page_zone(page), classzone))
 			continue;
 
+		max_scan--;
+
 		/* Racy check to avoid trylocking when not worthwhile */
 		if (!page->buffers && (page_count(page) != 1 || !page->mapping))
 			goto page_mapped;
@@ -516,11 +538,7 @@
 				if (nr_pages <= 0)
 					goto out;
 
-				shrink_dcache_memory(vm_vfs_scan_ratio, gfp_mask);
-				shrink_icache_memory(vm_vfs_scan_ratio, gfp_mask);
-#ifdef CONFIG_QUOTA
-				shrink_dqcache_memory(vm_vfs_scan_ratio, gfp_mask);
-#endif
+				shrink_vfs_caches(1, gfp_mask);
 
 				if (!*failed_swapout)
 					*failed_swapout = !swap_out(classzone);
@@ -614,6 +632,8 @@
 	if (nr_pages <= 0)
 		goto out;
 
+	shrink_vfs_caches(0, gfp_mask);
+
 	spin_lock(&pagemap_lru_lock);
 	refill_inactive(nr_pages, classzone);
 
@@ -638,11 +658,9 @@
 			nr_pages = shrink_caches(classzone, gfp_mask, nr_pages, &failed_swapout);
 			if (nr_pages <= 0)
 				return 1;
-			shrink_dcache_memory(vm_vfs_scan_ratio, gfp_mask);
-			shrink_icache_memory(vm_vfs_scan_ratio, gfp_mask);
-#ifdef CONFIG_QUOTA
-			shrink_dqcache_memory(vm_vfs_scan_ratio, gfp_mask);
-#endif
+
+			shrink_vfs_caches(1, gfp_mask);
+
 			if (!failed_swapout)
 				failed_swapout = !swap_out(classzone);
 		} while (--tries);
--- ./include/linux/swap.h.~1~	2003-09-16 20:46:35.000000000 -0400
+++ ./include/linux/swap.h	2003-09-21 00:56:23.000000000 -0400
@@ -116,6 +116,7 @@
 extern int FASTCALL(try_to_free_pages_zone(zone_t *, unsigned int));
 extern int FASTCALL(try_to_free_pages(unsigned int));
 extern int vm_vfs_scan_ratio, vm_cache_scan_ratio, vm_lru_balance_ratio, vm_passes, vm_gfp_debug, vm_mapped_ratio;
+extern int vm_vfs_scan_interval;
 
 /* linux/mm/page_io.c */
 extern void rw_swap_page(int, struct page *);
--- ./include/linux/sysctl.h.~1~	2003-09-16 20:46:35.000000000 -0400
+++ ./include/linux/sysctl.h	2003-09-21 00:59:37.000000000 -0400
@@ -154,6 +154,7 @@
 	VM_GFP_DEBUG=18,        /* debug GFP failures */
 	VM_CACHE_SCAN_RATIO=19, /* part of the inactive cache list to scan */
 	VM_MAPPED_RATIO=20,     /* amount of unfreeable pages that triggers swapout */
+	VM_VFS_SCAN_INTERVAL=21,/* interval (in secs) between reclaiming memory from inode/dentry cache */
 };