Re: [PATCH] swapin readahead v4

[Rik van Riel <H.H.vanRiel@phys.uu.nl>]

On Thu, 3 Dec 1998, Stephen C. Tweedie wrote:

> > Stephen's messages gave away the clue to something I was just
> > about to track down myself. Anyway, here is the 4th version of
> > my swapin readahead patch.
> 
> Much better to do this after calling read_swap_cache_async(): it's bad
> policy to make the reference count of the page after calling this
> function dependent on the arguments: that is a maintenance nightmare.  
> 
> Oh, and you _still_ need to check the swap_lockmap before calling
> read_swap_cache_async(), and you still have the extra break() in the
> readahead loop...

Somebody forbid me to do coding while having a flu...

This patch (v5) should be much better (I haven't tried it
yet but it has all things Stephen told me to include -- as
far as I can see through the haze that surrounds me).

cheers,

Rik -- the flu hits, the flu hits, the flu hits -- MORE
+-------------------------------------------------------------------+
| Linux memory management tour guide.        H.H.vanRiel@phys.uu.nl |
| Scouting Vries cubscout leader.      http://www.phys.uu.nl/~riel/ |
+-------------------------------------------------------------------+

--- ./mm/vmscan.c.orig	Thu Nov 26 11:26:50 1998
+++ ./mm/vmscan.c	Tue Dec  1 07:12:28 1998
@@ -431,6 +431,8 @@
 	kmem_cache_reap(gfp_mask);
 
 	if (buffer_over_borrow() || pgcache_over_borrow())
+		state = 0;		
+	if (atomic_read(&nr_async_pages) > pager_daemon.swap_cluster / 2)
 		shrink_mmap(i, gfp_mask);
 
 	switch (state) {
--- ./mm/page_io.c.orig	Thu Nov 26 11:26:49 1998
+++ ./mm/page_io.c	Thu Nov 26 11:30:43 1998
@@ -60,7 +60,7 @@
 	}
 
 	/* Don't allow too many pending pages in flight.. */
-	if (atomic_read(&nr_async_pages) > SWAP_CLUSTER_MAX)
+	if (atomic_read(&nr_async_pages) > pager_daemon.swap_cluster)
 		wait = 1;
 
 	p = &swap_info[type];
--- ./mm/page_alloc.c.orig	Thu Nov 26 11:26:49 1998
+++ ./mm/page_alloc.c	Thu Dec  3 14:26:25 1998
@@ -370,9 +370,31 @@
 	pte_t * page_table, unsigned long entry, int write_access)
 {
 	unsigned long page;
-	struct page *page_map;
-	
+	int i;
+	struct page *new_page, *page_map = lookup_swap_cache(entry);
+	unsigned long offset = SWP_OFFSET(entry);
+	struct swap_info_struct *swapdev = SWP_TYPE(entry) + swap_info;
+
+	if (!page_map) {	
 	page_map = read_swap_cache(entry);
+
+	/*
+	 * Primitive swap readahead code. We simply read the
+	 * next 16 entries in the swap area. The break below
+	 * is needed or else the request queue will explode :)
+	 */
+	  for (i = 1; i++ < 16;) {
+		offset++;
+		if (!swapdev->swap_map[offset] || offset >= swapdev->max
+			|| nr_free_pages - atomic_read(&nr_async_pages) <
+				(freepages.high + freepages.low)/2 ||
+				test_bit(offset, swapdev->swap_lockmap))
+			continue;
+			new_page = read_swap_cache_async(SWP_ENTRY(SWP_TYPE(entry), offset), 0);
+			if (new_page)
+				__free_page(new_page);
+	  }
+	}
 
 	if (pte_val(*page_table) != entry) {
 		if (page_map)
--- ./mm/swap_state.c.orig	Thu Nov 26 11:26:49 1998
+++ ./mm/swap_state.c	Thu Dec  3 14:19:19 1998
@@ -258,7 +258,7 @@
  * incremented.
  */
 
-static struct page * lookup_swap_cache(unsigned long entry)
+struct page * lookup_swap_cache(unsigned long entry)
 {
 	struct page *found;
 	
--- ./include/linux/swap.h.orig	Tue Dec  1 07:29:56 1998
+++ ./include/linux/swap.h	Tue Dec  1 07:31:03 1998
@@ -90,6 +90,7 @@
 extern struct page * read_swap_cache_async(unsigned long, int);
 #define read_swap_cache(entry) read_swap_cache_async(entry, 1);
 extern int FASTCALL(swap_count(unsigned long));
+extern struct page * lookup_swap_cache(unsigned long); 
 /*
  * Make these inline later once they are working properly.
  */

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