Is there a way to turn file caching off ?

Is there a way to turn file caching off ?

[Laurent Chavet]

Hi,

I'm running on a machine with 2GB of memory and dual PIII 550MHZ.
Just after boot with "nothing else running":
I run a program that almost like dd if=/dev/null of=/local/test
count=10000 bs=1000000
Except that there is a thread for reading and a thread for writing.
The program itself almost doesn't take any CPU.
What's going on is top showing:
    First cache grows to the size of RAM (2GB) with transfer rate
slowing down as the cache grows.
    Then the transfer rates drops a lot (2 to 3 time slower than the
drive capacity) and there is a very high CPU usage of system time (more
than a CPU) used by bdflush and kswapd (and some others like kupdated).

Of course my real application doesn't go from /dev/zero to file but it
still only does sequential access, and it seems that I pay a high price
for the file caching when I'm not using it at all.

Is there a way to turn file caching off, or at least limit its size ?

Thanks,

Laurent Chavet

RE: Is there a way to turn file caching off ?

[David Schwartz]

> Is there a way to turn file caching off, or at least limit its size ?
>
> Thanks,
>
> Laurent Chavet

	What benefit do you think you would get by limiting its size? All that
would do is ensure you hit the cache thrashing point sooner.

	DS

Re: Is there a way to turn file caching off ?

[Bjorn Wesen]

A similar phenomenon happens when you simply copy a file - file A is read
into the cache and file B is written to the cache, until the memory runs
out. Then both start to flush at the same time, creating a horrible
performance hit (especially if A and B are on the same disk :) 

I don't know a way to fix this except having the kernel correctly identify
the access pattern and optimize for it (i.e. if it recognizes that cache
pages are flushed in order to make room for more pages from the same
inode, then it's probably a suboptimal caching pattern and instead it
should probably increase the readahead and flush bigger chunks of pages at
the same time). I don't think anything can be done to the writing queue
(except maybe make the kernel understand that seek-time is more expensive
than transfer-time, so it does not schedule the read/writeing each odd
page..)

I'm still using 2.4.0 though so maybe this behaviour has been fixed to the
better in later kernels.. 

As a sidenote, try the same thing on an WinNT box and watch it die :) Like
unpacking a 1 GB file on a machine with 128 MB ram.. after it has unpacked
the first 100 MB's or so, performance drops to 1% or something..

-BW

On Tue, 17 Apr 2001, Laurent Chavet wrote:
>     First cache grows to the size of RAM (2GB) with transfer rate
> slowing down as the cache grows.
>     Then the transfer rates drops a lot (2 to 3 time slower than the
> drive capacity) and there is a very high CPU usage of system time (more
> than a CPU) used by bdflush and kswapd (and some others like kupdated).

Re: Is there a way to turn file caching off ?

[Jeremy Jackson]

Bjorn Wesen wrote:

> A similar phenomenon happens when you simply copy a file - file A is read
> into the cache and file B is written to the cache, until the memory runs
> out. Then both start to flush at the same time, creating a horrible

in this example only file B needs uses IO when being flushed; A's
buffers aren't dirty, so they're just 'forgotten'

>
> performance hit (especially if A and B are on the same disk :)
>

bdflush and 2.4's equivalent are tunable; if all you do is this copying
then optimise these parameters for this task.

>
> I don't know a way to fix this except having the kernel correctly identify
> the access pattern and optimize for it (i.e. if it recognizes that cache

currently all the kernel's heuristics are feed-back control loops.
what you are asking for is a feed-forward system: a way for the application
to tell kernel "I'm only reading this once, so after I'm done, throw it out
straight away"
and "I'm only writing this data, so after I'm done, start writing it out and
then forget it"

perhaps you could try mounting the destinatinon 'sync'
with dd at least you could specify block size,
there is also raw devices (no cache) mmaped files with madvise,
fdatasync()... lots of ways.

>
> pages are flushed in order to make room for more pages from the same
> inode, then it's probably a suboptimal caching pattern and instead it
> should probably increase the readahead and flush bigger chunks of pages at
> the same time). I don't think anything can be done to the writing queue
> (except maybe make the kernel understand that seek-time is more expensive
> than transfer-time, so it does not schedule the read/writeing each odd

there is the elevator seek mechanism...

>
> page..)
>
> I'm still using 2.4.0 though so maybe this behaviour has been fixed to the
> better in later kernels..
>
> As a sidenote, try the same thing on an WinNT box and watch it die :) Like
> unpacking a 1 GB file on a machine with 128 MB ram.. after it has unpacked
> the first 100 MB's or so, performance drops to 1% or something..

Isn't this due to the journaling filesystem?  All that seeking sure slows
things down...

>
>
> -BW
>
> On Tue, 17 Apr 2001, Laurent Chavet wrote:
> >     First cache grows to the size of RAM (2GB) with transfer rate
> > slowing down as the cache grows.
> >     Then the transfer rates drops a lot (2 to 3 time slower than the
> > drive capacity) and there is a very high CPU usage of system time (more
> > than a CPU) used by bdflush and kswapd (and some others like kupdated).
>
> -
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Very bad behavior of kswapd

[Laurent Chavet]

Try this (my example I've 2GB of ram)

turn all your swap off

dd about 15% of the size of your RAM:
dd if=/dev/zero of=/local/test count=300 bs=1000000

Run this program with SIZE about 95% of your RAM:

#include <stdlib.h>
#include <unistd.h>
#include <assert.h>

#define SIZE (1900 * 1024 * 1024)
int main()
{
  int i;
  char *p = malloc(SIZE);
  assert (p != NULL);
  for (i = 0; i < SIZE; i++)
 p[i] = 1;
  printf ("done %p\n", p);

  while (1)
  {
 sleep (60);
  }
  return 0;
}


Watch top: when this program needs the memory that kswapd keep in cache they go
both at 100% cpu (on SMP) but still the size of the program only grows at about
100KB/s, why is kswapd releasing it so slowly and taking so much CPU ?

Laurent Chavet

Re: Very bad behavior of kswapd

[Rik van Riel]

On Wed, 18 Apr 2001, Laurent Chavet wrote:

> Try this (my example I've 2GB of ram)
>
> turn all your swap off
>
> dd about 15% of the size of your RAM:
> dd if=/dev/zero of=/local/test count=300 bs=1000000
>
> Run this program with SIZE about 95% of your RAM:
>
> #include <stdlib.h>
> #include <unistd.h>
> #include <assert.h>
>
> #define SIZE (1900 * 1024 * 1024)
> int main()
> {
>   int i;
>   char *p = malloc(SIZE);
>   assert (p != NULL);
>   for (i = 0; i < SIZE; i++)
>  p[i] = 1;
>   printf ("done %p\n", p);
>
>   while (1)
>   {
>  sleep (60);
>   }
>   return 0;
> }
>
>
> Watch top: when this program needs the memory that kswapd keep
> in cache they go both at 100% cpu (on SMP) but still the size of
> the program only grows at about 100KB/s, why is kswapd releasing
> it so slowly and taking so much CPU ?

Because kswapd still has to scan all the (unfreeable) memory
of the big process to determine it isn't freeable.

At the moment kswapd is really stupid about these corner-case
situations, please bear with us while we fix it ...

... and don't forget to fill in a bugzilla item on the
Linux-MM bugzilla ;)

regards,

Rik
--
Linux MM bugzilla: http://linux-mm.org/bugzilla.shtml

Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

		http://www.surriel.com/
http://www.conectiva.com/	http://distro.conectiva.com/

Re: Very bad behavior of kswapd

[David S. Miller]

Rik van Riel writes:
 > > Watch top: when this program needs the memory that kswapd keep
 > > in cache they go both at 100% cpu (on SMP) but still the size of
 > > the program only grows at about 100KB/s, why is kswapd releasing
 > > it so slowly and taking so much CPU ?
 > 
 > Because kswapd still has to scan all the (unfreeable) memory
 > of the big process to determine it isn't freeable.

This is not the only badly performing case actually.  When one of ones
swap partitions gets close to full, kswapd basically sits endlessly in
get_swap_page() due to all the broken linear scan algorithms.  I've
tried to fix some of this with the patch below.

This may not be the case Laurent is seeing but it is a problem that
needs fixing.

--- ../vanilla/linux/include/linux/swap.h	Fri Apr 13 17:08:16 2001
+++ include/linux/swap.h	Sat Apr 14 00:10:02 2001
@@ -43,8 +43,22 @@
 
 #define SWAP_CLUSTER_MAX 32
 
-#define SWAP_MAP_MAX	0x7fff
-#define SWAP_MAP_BAD	0x8000
+#define SWAPFILE_CLUSTER 256
+
+struct swap_cluster_struct {
+	struct list_head	list;
+	int			nr_free;	/* 0 --> SWAPFILE_CLUSTER */
+	unsigned int		start_offset;
+};
+
+#define SWAP_MAP_MAX	0x7fffffff
+#define SWAP_MAP_BAD	0x80000000
+
+struct swap_map_struct {
+	struct list_head	list;
+	unsigned int		offset;
+	unsigned int		count;
+};
 
 struct swap_info_struct {
 	unsigned int flags;
@@ -52,11 +66,15 @@
 	spinlock_t sdev_lock;
 	struct dentry * swap_file;
 	struct vfsmount *swap_vfsmnt;
-	unsigned short * swap_map;
-	unsigned int lowest_bit;
-	unsigned int highest_bit;
-	unsigned int cluster_next;
-	unsigned int cluster_nr;
+	struct swap_map_struct * swap_maps;
+	struct list_head swap_map_free_list;
+
+	struct swap_cluster_struct * swap_clusters;
+	struct list_head swap_cluster_free_list;
+
+	struct swap_cluster_struct * curr_cluster;
+	unsigned int cluster_offset_next;
+
 	int prio;			/* swap priority */
 	int pages;
 	unsigned long max;
--- ../vanilla/linux/mm/swapfile.c	Thu Mar 22 09:22:15 2001
+++ mm/swapfile.c	Sat Apr 14 01:07:40 2001
@@ -24,62 +24,60 @@
 
 struct swap_info_struct swap_info[MAX_SWAPFILES];
 
-#define SWAPFILE_CLUSTER 256
-
-static inline int scan_swap_map(struct swap_info_struct *si, unsigned short count)
+static unsigned int scan_swap_map(struct swap_info_struct *si, unsigned int count)
 {
-	unsigned long offset;
-	/* 
-	 * We try to cluster swap pages by allocating them
-	 * sequentially in swap.  Once we've allocated
-	 * SWAPFILE_CLUSTER pages this way, however, we resort to
-	 * first-free allocation, starting a new cluster.  This
-	 * prevents us from scattering swap pages all over the entire
-	 * swap partition, so that we reduce overall disk seek times
-	 * between swap pages.  -- sct */
-	if (si->cluster_nr) {
-		while (si->cluster_next <= si->highest_bit) {
-			offset = si->cluster_next++;
-			if (si->swap_map[offset])
-				continue;
-			si->cluster_nr--;
-			goto got_page;
-		}
-	}
-	si->cluster_nr = SWAPFILE_CLUSTER;
+	struct swap_map_struct *map;
+	struct list_head *head, *tmp;
 
-	/* try to find an empty (even not aligned) cluster. */
-	offset = si->lowest_bit;
- check_next_cluster:
-	if (offset+SWAPFILE_CLUSTER-1 <= si->highest_bit)
-	{
-		int nr;
-		for (nr = offset; nr < offset+SWAPFILE_CLUSTER; nr++)
-			if (si->swap_map[nr])
-			{
-				offset = nr+1;
-				goto check_next_cluster;
-			}
-		/* We found a completly empty cluster, so start
-		 * using it.
+	/* Any swap entries left at all? */
+	if (list_empty(&si->swap_map_free_list))
+		return 0;
+
+get_from_cluster:
+
+	/* Currently allocating from a cluster? */
+	if (si->curr_cluster != NULL) {
+		struct swap_cluster_struct *cluster = si->curr_cluster;
+		unsigned int offset = si->cluster_offset_next;
+
+		/* Note that this test cannot be made with cluster->nr_free
+		 * because it is possible for a swap entry to be freed before
+		 * we are done allocating from this cluster.
 		 */
-		goto got_page;
+		if (si->cluster_offset_next++ == SWAPFILE_CLUSTER)
+			si->curr_cluster = NULL;
+
+		cluster->nr_free--;
+
+		map = &si->swap_maps[offset];
+		goto finish_alloc;
 	}
-	/* No luck, so now go finegrined as usual. -Andrea */
-	for (offset = si->lowest_bit; offset <= si->highest_bit ; offset++) {
-		if (si->swap_map[offset])
-			continue;
-	got_page:
-		if (offset == si->lowest_bit)
-			si->lowest_bit++;
-		if (offset == si->highest_bit)
-			si->highest_bit--;
-		si->swap_map[offset] = count;
-		nr_swap_pages--;
-		si->cluster_next = offset+1;
-		return offset;
+
+	/* Can we start a new cluster? */
+	head = &si->swap_cluster_free_list;
+	if (!list_empty(head)) {
+		struct swap_cluster_struct *cluster;
+
+		tmp = head->next;
+		cluster = list_entry(tmp, struct swap_cluster_struct, list);
+		list_del(tmp);
+		si->cluster_offset_next = cluster->start_offset;
+		si->curr_cluster = cluster;
+		goto get_from_cluster;
 	}
-	return 0;
+
+	/* Fragmented, no clusters, get individual entry. */
+	head = &si->swap_map_free_list;
+	tmp = head->next;
+	map = list_entry(tmp, struct swap_map_struct, list);
+	si->swap_clusters[map->offset / SWAPFILE_CLUSTER].nr_free--;
+
+finish_alloc:
+
+	list_del(&map->list);
+	map->count = count;
+	nr_swap_pages--;
+	return map->offset;
 }
 
 swp_entry_t __get_swap_page(unsigned short count)
@@ -145,6 +143,7 @@
 void __swap_free(swp_entry_t entry, unsigned short count)
 {
 	struct swap_info_struct * p;
+	struct swap_map_struct * map;
 	unsigned long offset, type;
 
 	if (!entry.val)
@@ -159,21 +158,37 @@
 	offset = SWP_OFFSET(entry);
 	if (offset >= p->max)
 		goto bad_offset;
-	if (!p->swap_map[offset])
+	map = p->swap_maps + offset;
+
+	if (!map->count)
 		goto bad_free;
 	swap_list_lock();
 	if (p->prio > swap_info[swap_list.next].prio)
 		swap_list.next = type;
 	swap_device_lock(p);
-	if (p->swap_map[offset] < SWAP_MAP_MAX) {
-		if (p->swap_map[offset] < count)
+	if (map->count < SWAP_MAP_MAX) {
+		if (map->count < count)
 			goto bad_count;
-		if (!(p->swap_map[offset] -= count)) {
-			if (offset < p->lowest_bit)
-				p->lowest_bit = offset;
-			if (offset > p->highest_bit)
-				p->highest_bit = offset;
+		if (!(map->count -= count)) {
+			unsigned int clust_nr = offset / SWAPFILE_CLUSTER;
+			struct swap_cluster_struct *cluster;
+
+			/* Add to tail so that clusters are more likely to
+			 * build up.
+			 */
+			list_add_tail(&map->list, &p->swap_map_free_list);
 			nr_swap_pages++;
+
+			cluster = p->swap_clusters + clust_nr;
+			if (cluster->nr_free++ == SWAPFILE_CLUSTER) {
+				if (p->curr_cluster == cluster)
+					BUG();
+
+				list_add(&cluster->list,
+					 &p->swap_cluster_free_list);
+			}
+			if (cluster->nr_free > SWAPFILE_CLUSTER)
+				BUG();
 		}
 	}
 	swap_device_unlock(p);
@@ -196,7 +211,8 @@
 bad_count:
 	swap_device_unlock(p);
 	swap_list_unlock();
-	printk(KERN_ERR "VM: Bad count %hd current count %hd\n", count, p->swap_map[offset]);
+	printk(KERN_ERR "VM: Bad count %hd current count %hd\n", count,
+	       p->swap_maps[offset].count);
 	goto out;
 }
 
@@ -347,15 +363,16 @@
 		 */
 		swap_device_lock(si);
 		for (i = 1; i < si->max ; i++) {
-			if (si->swap_map[i] > 0 && si->swap_map[i] != SWAP_MAP_BAD) {
+			if (si->swap_maps[i].count > 0 &&
+			    si->swap_maps[i].count != SWAP_MAP_BAD) {
 				/*
 				 * Prevent swaphandle from being completely
 				 * unused by swap_free while we are trying
 				 * to read in the page - this prevents warning
 				 * messages from rw_swap_page_base.
 				 */
-				if (si->swap_map[i] != SWAP_MAP_MAX)
-					si->swap_map[i]++;
+				if (si->swap_maps[i].count != SWAP_MAP_MAX)
+					si->swap_maps[i].count++;
 				swap_device_unlock(si);
 				goto found_entry;
 			}
@@ -390,12 +407,28 @@
 		swap_free(entry);
 		swap_list_lock();
 		swap_device_lock(si);
-		if (si->swap_map[i] > 0) {
-			if (si->swap_map[i] != SWAP_MAP_MAX)
+		if (si->swap_maps[i].count > 0) {
+			unsigned int clust_nr = i / SWAPFILE_CLUSTER;
+			struct swap_cluster_struct *cluster;
+
+			if (si->swap_maps[i].count != SWAP_MAP_MAX)
 				printk("VM: Undead swap entry %08lx\n", 
-								entry.val);
+				       entry.val);
 			nr_swap_pages++;
-			si->swap_map[i] = 0;
+			list_add_tail(&si->swap_maps[i].list, &si->swap_map_free_list);
+			si->swap_maps[i].count = 0;
+
+			/* Keep the cluster state sane just in case
+			 * swap_off fails.
+			 */
+			cluster = si->swap_clusters + clust_nr;
+			if (cluster->nr_free++ == SWAPFILE_CLUSTER) {
+				if (si->curr_cluster == cluster)
+					BUG();
+
+				list_add(&cluster->list,
+					 &si->swap_cluster_free_list);
+			}
 		}
 		swap_device_unlock(si);
 		swap_list_unlock();
@@ -478,8 +511,13 @@
 	nd.mnt = p->swap_vfsmnt;
 	p->swap_vfsmnt = NULL;
 	p->swap_device = 0;
-	vfree(p->swap_map);
-	p->swap_map = NULL;
+	vfree(p->swap_maps);
+	p->swap_maps = NULL;
+	INIT_LIST_HEAD(&p->swap_map_free_list);
+	vfree(p->swap_clusters);
+	p->swap_clusters = NULL;
+	INIT_LIST_HEAD(&p->swap_cluster_free_list);
+	p->curr_cluster = NULL;
 	p->flags = 0;
 	err = 0;
 
@@ -514,7 +552,7 @@
 
 			usedswap = 0;
 			for (j = 0; j < ptr->max; ++j)
-				switch (ptr->swap_map[j]) {
+				switch (ptr->swap_maps[j].count) {
 					case SWAP_MAP_BAD:
 					case 0:
 						continue;
@@ -578,10 +616,11 @@
 	p->swap_file = NULL;
 	p->swap_vfsmnt = NULL;
 	p->swap_device = 0;
-	p->swap_map = NULL;
-	p->lowest_bit = 0;
-	p->highest_bit = 0;
-	p->cluster_nr = 0;
+	p->swap_maps = NULL;
+	INIT_LIST_HEAD(&p->swap_map_free_list);
+	p->swap_clusters = NULL;
+	INIT_LIST_HEAD(&p->swap_cluster_free_list);
+	p->curr_cluster = NULL;
 	p->sdev_lock = SPIN_LOCK_UNLOCKED;
 	p->max = 1;
 	p->next = -1;
@@ -666,28 +705,28 @@
 	case 1:
 		memset(((char *) swap_header)+PAGE_SIZE-10,0,10);
 		j = 0;
-		p->lowest_bit = 0;
-		p->highest_bit = 0;
 		for (i = 1 ; i < 8*PAGE_SIZE ; i++) {
 			if (test_bit(i,(char *) swap_header)) {
-				if (!p->lowest_bit)
-					p->lowest_bit = i;
-				p->highest_bit = i;
 				p->max = i+1;
 				j++;
 			}
 		}
 		nr_good_pages = j;
-		p->swap_map = vmalloc(p->max * sizeof(short));
-		if (!p->swap_map) {
+		p->swap_maps = vmalloc(p->max * sizeof(struct swap_map_struct));
+		if (!p->swap_maps) {
 			error = -ENOMEM;		
 			goto bad_swap;
 		}
 		for (i = 1 ; i < p->max ; i++) {
-			if (test_bit(i,(char *) swap_header))
-				p->swap_map[i] = 0;
-			else
-				p->swap_map[i] = SWAP_MAP_BAD;
+			p->swap_maps[i].offset = i;
+			INIT_LIST_HEAD(&p->swap_maps[i].list);
+			if (test_bit(i,(char *) swap_header)) {
+				p->swap_maps[i].count = 0;
+				list_add_tail(&p->swap_maps[i].list,
+					      &p->swap_map_free_list);
+			} else {
+				p->swap_maps[i].count = SWAP_MAP_BAD;
+			}
 		}
 		break;
 
@@ -702,8 +741,6 @@
 			goto bad_swap;
 		}
 
-		p->lowest_bit  = 1;
-		p->highest_bit = swap_header->info.last_page - 1;
 		p->max	       = swap_header->info.last_page;
 
 		maxpages = SWP_OFFSET(SWP_ENTRY(0,~0UL));
@@ -715,19 +752,27 @@
 			goto bad_swap;
 		
 		/* OK, set up the swap map and apply the bad block list */
-		if (!(p->swap_map = vmalloc (p->max * sizeof(short)))) {
+		if (!(p->swap_maps = vmalloc (p->max * sizeof(struct swap_map_struct)))) {
 			error = -ENOMEM;
 			goto bad_swap;
 		}
 
 		error = 0;
-		memset(p->swap_map, 0, p->max * sizeof(short));
+		for (i = 0; i < p->max; i++) {
+			INIT_LIST_HEAD(&p->swap_maps[i].list);
+			p->swap_maps[i].offset = i;
+			p->swap_maps[i].count = 0;
+			list_add_tail(&p->swap_maps[i].list,
+				      &p->swap_map_free_list);
+		}
 		for (i=0; i<swap_header->info.nr_badpages; i++) {
 			int page = swap_header->info.badpages[i];
-			if (page <= 0 || page >= swap_header->info.last_page)
+			if (page <= 0 || page >= swap_header->info.last_page) {
 				error = -EINVAL;
-			else
-				p->swap_map[page] = SWAP_MAP_BAD;
+			} else {
+				p->swap_maps[page].count = SWAP_MAP_BAD;
+				list_del(&p->swap_maps[page].list);
+			}
 		}
 		nr_good_pages = swap_header->info.last_page -
 				swap_header->info.nr_badpages -
@@ -736,6 +781,34 @@
 			goto bad_swap;
 	}
 	
+	p->swap_clusters = vmalloc((p->max / SWAPFILE_CLUSTER)
+				   * sizeof(struct swap_cluster_struct));
+	if (!p->swap_clusters) {
+		error = -ENOMEM;
+		goto bad_swap;
+	}
+	for (i = 0; i < (p->max / SWAPFILE_CLUSTER); i++) {
+		INIT_LIST_HEAD(&p->swap_clusters[i].list);
+		p->swap_clusters[i].nr_free = 0;
+		p->swap_clusters[i].start_offset = (i * SWAPFILE_CLUSTER);
+	}
+
+	/* Swap entry zero can never be allocated, therefore
+	 * swap cluster zero can never be either.
+	 */
+	for (i = 1; i < p->max; i++) {
+		int cluster = i / SWAPFILE_CLUSTER;
+
+		if (p->swap_maps[i].count != SWAP_MAP_BAD) {
+			if (p->swap_clusters[cluster].nr_free++ == SWAPFILE_CLUSTER)
+				list_add(&p->swap_clusters[cluster].list,
+					 &p->swap_cluster_free_list);
+
+			if (p->swap_clusters[cluster].nr_free > SWAPFILE_CLUSTER)
+				BUG();
+		}
+	}
+
 	if (swapfilesize && p->max > swapfilesize) {
 		printk(KERN_WARNING
 		       "Swap area shorter than signature indicates\n");
@@ -747,7 +820,8 @@
 		error = -EINVAL;
 		goto bad_swap;
 	}
-	p->swap_map[0] = SWAP_MAP_BAD;
+	p->swap_maps[0].count = SWAP_MAP_BAD;
+	list_del(&p->swap_maps[0].list);
 	p->flags = SWP_WRITEOK;
 	p->pages = nr_good_pages;
 	swap_list_lock();
@@ -776,14 +850,22 @@
 	if (bdev)
 		blkdev_put(bdev, BDEV_SWAP);
 bad_swap_2:
-	if (p->swap_map)
-		vfree(p->swap_map);
+	if (p->swap_maps) {
+		vfree(p->swap_maps);
+		p->swap_maps = NULL;
+		INIT_LIST_HEAD(&p->swap_map_free_list);
+	}
+	if (p->swap_clusters) {
+		vfree(p->swap_clusters);
+		p->swap_clusters = NULL;
+		INIT_LIST_HEAD(&p->swap_cluster_free_list);
+		p->curr_cluster = NULL;
+	}
 	nd.mnt = p->swap_vfsmnt;
 	nd.dentry = p->swap_file;
 	p->swap_device = 0;
 	p->swap_file = NULL;
 	p->swap_vfsmnt = NULL;
-	p->swap_map = NULL;
 	p->flags = 0;
 	if (!(swap_flags & SWAP_FLAG_PREFER))
 		++least_priority;
@@ -806,7 +888,7 @@
 		if ((swap_info[i].flags & SWP_WRITEOK) != SWP_WRITEOK)
 			continue;
 		for (j = 0; j < swap_info[i].max; ++j) {
-			switch (swap_info[i].swap_map[j]) {
+			switch (swap_info[i].swap_maps[j].count) {
 				case SWAP_MAP_BAD:
 					continue;
 				case 0:
@@ -825,7 +907,7 @@
  * Verify that a swap entry is valid and increment its swap map count.
  * Kernel_lock is held, which guarantees existance of swap device.
  *
- * Note: if swap_map[] reaches SWAP_MAP_MAX the entries are treated as
+ * Note: if swap_maps[].count reaches SWAP_MAP_MAX the entries are treated as
  * "permanent", but will be reclaimed by the next swapoff.
  */
 int swap_duplicate(swp_entry_t entry)
@@ -844,19 +926,19 @@
 	offset = SWP_OFFSET(entry);
 	if (offset >= p->max)
 		goto bad_offset;
-	if (!p->swap_map[offset])
+	if (!p->swap_maps[offset].count)
 		goto bad_unused;
 	/*
 	 * Entry is valid, so increment the map count.
 	 */
 	swap_device_lock(p);
-	if (p->swap_map[offset] < SWAP_MAP_MAX)
-		p->swap_map[offset]++;
+	if (p->swap_maps[offset].count < SWAP_MAP_MAX)
+		p->swap_maps[offset].count++;
 	else {
 		static int overflow = 0;
 		if (overflow++ < 5)
 			printk("VM: swap entry overflow\n");
-		p->swap_map[offset] = SWAP_MAP_MAX;
+		p->swap_maps[offset].count = SWAP_MAP_MAX;
 	}
 	swap_device_unlock(p);
 	result = 1;
@@ -895,9 +977,9 @@
 	offset = SWP_OFFSET(entry);
 	if (offset >= p->max)
 		goto bad_offset;
-	if (!p->swap_map[offset])
+	if (!p->swap_maps[offset].count)
 		goto bad_unused;
-	retval = p->swap_map[offset];
+	retval = p->swap_maps[offset].count;
 out:
 	return retval;
 
@@ -936,7 +1018,7 @@
 		printk("rw_swap_page: weirdness\n");
 		return;
 	}
-	if (p->swap_map && !p->swap_map[*offset]) {
+	if (p->swap_maps && !p->swap_maps[*offset].count) {
 		printk("VM: Bad swap entry %08lx\n", entry.val);
 		return;
 	}
@@ -975,11 +1057,11 @@
 		if (toff >= swapdev->max)
 			break;
 		/* Don't read in bad or busy pages */
-		if (!swapdev->swap_map[toff])
+		if (!swapdev->swap_maps[toff].count)
 			break;
-		if (swapdev->swap_map[toff] == SWAP_MAP_BAD)
+		if (swapdev->swap_maps[toff].count == SWAP_MAP_BAD)
 			break;
-		swapdev->swap_map[toff]++;
+		swapdev->swap_maps[toff].count++;
 		toff++;
 		ret++;
 	} while (--i);

Re: Is there a way to turn file caching off ?

[Helge Hafting]

Jeremy Jackson wrote:

> currently all the kernel's heuristics are feed-back control loops.
> what you are asking for is a feed-forward system: a way for the application
> to tell kernel "I'm only reading this once, so after I'm done, throw it out
> straight away"
> and "I'm only writing this data, so after I'm done, start writing it out and
> then forget it"
> 
This is hard to get right.  Sure - your unpack/copy program read once
and
writes once.  But the stuff might be used shortly thereafter by
another process.  For example:  I unpack a kernel tarball.  tar
knows it writes only once and might not need more than 5M to do
this as efficient as possible with my disks.  A lot of other cache
could be saved, fewer things swapped out.
But then I compile it.  Todays system ensures that lots of the source
is in memory already.  Limiting the caching to what tar needed
however will force the source to be read from disk once during
the compile - not what I want at all.  

A program may know its own access pattern, but it don't usually know
future access patterns.  Well, backing up the entire fs could benefit
from a something like this, you probably won't need the backup again
soon.  But this is hard to know in many other cases.

Helge Hafting

Re: Is there a way to turn file caching off ?

[Jeremy Jackson]

Helge Hafting wrote:

> Jeremy Jackson wrote:
>
> > currently all the kernel's heuristics are feed-back control loops.
> > what you are asking for is a feed-forward system: a way for the application
> > to tell kernel "I'm only reading this once, so after I'm done, throw it out
> > straight away"
> > and "I'm only writing this data, so after I'm done, start writing it out and
> > then forget it"
> >
> This is hard to get right.  Sure - your unpack/copy program read once
> and
> writes once.  But the stuff might be used shortly thereafter by
> another process.  For example:  I unpack a kernel tarball.  tar
> knows it writes only once and might not need more than 5M to do
> this as efficient as possible with my disks.  A lot of other cache
> could be saved, fewer things swapped out.
> But then I compile it.  Todays system ensures that lots of the source
> is in memory already.  Limiting the caching to what tar needed
> however will force the source to be read from disk once during
> the compile - not what I want at all.

They why would you tell tar not to use cache?  If you know what's happening
next you need to tell the system (feed-forward), not have it try to read your
mind.  I'm assuming your modified tar would have an option switch
to cause this behaviour, not be hard coded...

>
>
> A program may know its own access pattern, but it don't usually know
> future access patterns.  Well, backing up the entire fs could benefit

Yes, so a script that does the above wouldn't enable no cache mode
for written files.  The program doesn't know, but the encompasing
script (or person at console) does.

>
> from a something like this, you probably won't need the backup again
> soon.  But this is hard to know in many other cases.

Re: Is there a way to turn file caching off ?

[John Lenton]

On Thu, Apr 19, 2001 at 10:21:14AM +0200, Helge Hafting wrote:
> A program may know its own access pattern, but it don't usually know
> future access patterns.  Well, backing up the entire fs could benefit
> from a something like this, you probably won't need the backup again
> soon.  But this is hard to know in many other cases.

tar --please-leave-this-in-cache-pretty-please ?

-- 
John Lenton (john@grulic.org.ar) -- Random fortune:
Si los bugs te abruman, cierra tu Windows.