[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.

diff --git a/Documentation/filesystems/tmpfs.txt b/Documentation/filesystems/tmpfs.txt
index f33ed851e768f8c06a0454446ae838442adfba00..177edbea9bf11b070cfa124c4237785c45257bb4 100644 (file)
--- a/Documentation/filesystems/tmpfs.txt
+++ b/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 
+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.
+           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 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

diff --git a/mm/shmem.c b/mm/shmem.c
index ca44cbbf438ea107ccd1bb5bd3d20dac452c2e52..b19cfc88b363fc6526bd667560747a04196353e2 100644 (file)
--- a/mm/shmem.c
+++ b/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)) {