[PATCH] tmpfs 6/6: percentile sizing of tmpfs

From: CaT <cat@zip.com.au>

What this patch does is allow you to specify the max amount of memory tmpfs
can use as a percentage of available real ram.  This (in my eyes) is useful
so that you do not have to remember to change the setting if you want
something other then 50% and some of your ram goes.

Hugh redid the arithmetic to not overflow at 4GB; the particular order of
lines helps RH's gcc-2.96-110 not to get confused in the do_div.  2.5 can use
totalram_pages.  Update mount options in tmpfs Doc.

There's an argument that the percentage should be of ram+swap, that's what
Christoph originally intended.  But we set the default at 50% of ram only, so
I believe it's more consistent to follow that precedent.

Documentation/filesystems/tmpfs.txt

@@ -54,18 +54,21 @@ tmpfs has the following uses:
 4) And probably a lot more I do not know about :-)
 
 
-tmpfs has a couple of mount options:
+tmpfs has three mount options for sizing:
 
 size:      The limit of allocated bytes for this tmpfs instance. The 
            default is half of your physical RAM without swap. If you
            oversize your tmpfs instances the machine will deadlock
            since the OOM handler will not be able to free that memory.
-nr_blocks: The same as size, but in blocks of PAGECACHE_SIZE.
+nr_blocks: The same as size, but in blocks of PAGE_CACHE_SIZE.
 nr_inodes: The maximum number of inodes for this instance. The default
            is half of the number of your physical RAM pages.
 
 These parameters accept a suffix k, m or g for kilo, mega and giga and
-can be changed on remount.
+can be changed on remount.  The size parameter also accepts a suffix %
+to limit this tmpfs instance to that percentage of your physical RAM:
+the default, when neither size nor nr_blocks is specified, is size=50%
+
 
 To specify the initial root directory you can use the following mount
 options:
@@ -83,15 +86,7 @@ will give you tmpfs instance on /mytmpfs which can allocate 10GB
 RAM/SWAP in 10240 inodes and it is only accessible by root.
 
 
-TODOs:
-
-1) give the size option a percent semantic: If you give a mount option
-   size=50% the tmpfs instance should be able to grow to 50 percent of
-   RAM + swap. So the instance should adapt automatically if you add
-   or remove swap space.
-2) Show the number of tmpfs RAM pages. (As shared?)
-
 Author:
    Christoph Rohland <cr@sap.com>, 1.12.01
 Updated:
-   Hugh Dickins <hugh@veritas.com>, 17 Oct 2002
+   Hugh Dickins <hugh@veritas.com>, 01 April 2003

mm/shmem.c

@@ -35,6 +35,7 @@
 #include <linux/vfs.h>
 #include <linux/blkdev.h>
 #include <asm/uaccess.h>
+#include <asm/div64.h>
 
 /* This magic number is used in glibc for posix shared memory */
 #define TMPFS_MAGIC	0x01021994
@@ -1587,6 +1588,12 @@ static int shmem_parse_options(char *options, int *mode, uid_t *uid, gid_t *gid,
 		if (!strcmp(this_char,"size")) {
 			unsigned long long size;
 			size = memparse(value,&rest);
+			if (*rest == '%') {
+				size <<= PAGE_SHIFT;
+				size *= totalram_pages;
+				do_div(size, 100);
+				rest++;
+			}
 			if (*rest)
 				goto bad_val;
 			*blocks = size >> PAGE_CACHE_SHIFT;
@@ -1652,7 +1659,6 @@ static int shmem_fill_super(struct super_block *sb, void *data, int silent)
 	uid_t uid = current->fsuid;
 	gid_t gid = current->fsgid;
 	struct shmem_sb_info *sbinfo;
-	struct sysinfo si;
 	int err = -ENOMEM;
 
 	sbinfo = kmalloc(sizeof(struct shmem_sb_info), GFP_KERNEL);
@@ -1665,8 +1671,7 @@ static int shmem_fill_super(struct super_block *sb, void *data, int silent)
 	 * Per default we only allow half of the physical ram per
 	 * tmpfs instance
 	 */
-	si_meminfo(&si);
-	blocks = inodes = si.totalram / 2;
+	blocks = inodes = totalram_pages / 2;
 
 #ifdef CONFIG_TMPFS
 	if (shmem_parse_options(data, &mode, &uid, &gid, &blocks, &inodes)) {