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Subjectramfs limits (again)
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Yet another update to my ramfs resource limiting patch.

I realised that the removepage address_space_operations hook I added
(called from __remove_inode_page()) didn't really make sense. It is
now replaced with a "truncatepage" hook, called from
truncate_complete_page() (filemap.c). As a result, it now works with
recent kernels (tested, although not exhaustively, against test11).

There still seems to be a problem where sometimes the ramfs gets into
a state where it can't be unmounted (EBUSY). I have no idea what
triggers this as yet..

--
David Gibson, Technical Support Engineer, Linuxcare, Inc.
+61 2 6262 8990
dgibson@linuxcare.com, http://www.linuxcare.com/
Linuxcare. Support for the revolution.

diff -uNr test11/Documentation/filesystems/ramfs.txt test11-ramfs/Documentation/filesystems/ramfs.txt
--- test11/Documentation/filesystems/ramfs.txt Thu Jan 1 10:00:00 1970
+++ test11-ramfs/Documentation/filesystems/ramfs.txt Mon Nov 20 16:00:47 2000
@@ -0,0 +1,47 @@
+ ramfs - An automatically resizing memory based filesystem
+
+
+ Ramfs is a file system which keeps all files in RAM. It allows read
+ and write access. In contrast to RAM disks, which get allocated a
+ fixed amount of RAM, ramfs grows and shrinks to accommodate the
+ files it contains.
+
+ You can mount the ramfs with:
+ mount -t ramfs none /mnt/wherever
+
+ Then just create and use files. When the filesystem is unmounted, all
+ its contents are lost.
+
+ NOTE! This filesystem is probably most useful not as a real
+ filesystem, but as an example of how virtual filesystems can be
+ written.
+
+Resource limits:
+
+By default a ramfs will be limited to using half of (physical) memory
+for storing file contents, a bit over that when the metadata is
+included. The resource usage limits of ramfs can be controlled with
+the following mount options:
+
+ maxsize=NNN
+ Sets the maximum allowed memory usage of the
+filesystem to NNN kilobytes. This will be rounded down to a multiple
+of the page size. The default is half of physical memory. NB. unlike
+most of the other limits, setting this to zero does *not* mean no
+limit, but will actually limit the size of the filesystem data to zero
+pages. There might be a use for this in some perverse situation.
+
+ maxfilesize=NNN
+ Sets the maximum size of a single file on the
+filesystem to NNN kilobytes. This will be rounded down to a multiple
+of the page size. If NNN=0 there is no limit. The default is no limit.
+
+ maxdentries=NNN
+ Sets the maximum number of directory entries (hard
+links) on the filesystem to NNN. If NNN=0 there is no limit. By
+default this is set to maxsize/4.
+
+ maxinodes=NNN
+ Sets the maximum number of inodes (i.e. distinct
+files) on the filesystem to NNN. If NNN=0 there is no limit. The
+default is no limit (but there can never be more inodes than dentries).
diff -uNr test11/fs/ramfs/inode.c test11-ramfs/fs/ramfs/inode.c
--- test11/fs/ramfs/inode.c Mon Nov 20 14:05:34 2000
+++ test11-ramfs/fs/ramfs/inode.c Tue Nov 21 17:29:09 2000
@@ -4,6 +4,7 @@
* Copyright (C) 2000 Linus Torvalds.
* 2000 Transmeta Corp.
*
+ * Usage limits added by David Gibson, Linuxcare Australia.
* This file is released under the GPL.
*/

@@ -28,8 +29,18 @@
#include <linux/init.h>
#include <linux/string.h>
#include <linux/locks.h>
+#include <linux/highmem.h>
+#include <linux/malloc.h>

#include <asm/uaccess.h>
+#include <linux/spinlock.h>
+
+#if PAGE_CACHE_SIZE % 1024
+#error Oh no, PAGE_CACHE_SIZE is not divisible by 1k! I cannot cope.
+#endif
+
+#define IBLOCKS_PER_PAGE (PAGE_CACHE_SIZE / 512)
+#define K_PER_PAGE (PAGE_CACHE_SIZE / 1024)

/* some random number */
#define RAMFS_MAGIC 0x858458f6
@@ -40,8 +51,176 @@
static struct file_operations ramfs_file_operations;
static struct inode_operations ramfs_dir_inode_operations;

+/*
+ * ramfs super-block data in memory
+ */
+struct ramfs_sb_info {
+ /* Prevent races accessing the used block
+ * counts. Conceptually, this could probably be a semaphore,
+ * but the only thing we do while holding the lock is
+ * arithmetic, so there's no point */
+ spinlock_t ramfs_lock;
+
+ /* It is important that at least the free counts below be
+ signed. free_XXX may become negative if a limit is changed
+ downwards (by a remount) below the current usage. */
+
+ /* maximum number of pages in a file */
+ long max_file_pages;
+
+ /* max total number of data pages */
+ long max_pages;
+ /* free_pages = max_pages - total number of pages currently in use */
+ long free_pages;
+
+ /* max number of inodes */
+ long max_inodes;
+ /* free_inodes = max_inodes - total number of inodes currently in use */
+ long free_inodes;
+
+ /* max number of dentries */
+ long max_dentries;
+ /* free_dentries = max_dentries - total number of dentries in use */
+ long free_dentries;
+};
+
+#define RAMFS_SB(sb) ((struct ramfs_sb_info *)((sb)->u.generic_sbp))
+
+/*
+ * Resource limit helper functions
+ */
+
+static inline void lock_rsb(struct ramfs_sb_info *rsb)
+{
+ spin_lock(&(rsb->ramfs_lock));
+}
+
+static inline void unlock_rsb(struct ramfs_sb_info *rsb)
+{
+ spin_unlock(&(rsb->ramfs_lock));
+}
+
+/* Decrements the free inode count and returns true, or returns false
+ * if there are no free inodes */
+static int ramfs_alloc_inode(struct super_block *sb)
+{
+ struct ramfs_sb_info *rsb = RAMFS_SB(sb);
+ int ret = 1;
+
+ lock_rsb(rsb);
+ if (!rsb->max_inodes || rsb->free_inodes > 0)
+ rsb->free_inodes--;
+ else
+ ret = 0;
+ unlock_rsb(rsb);
+
+ return ret;
+}
+
+/* Increments the free inode count */
+static void ramfs_dealloc_inode(struct super_block *sb)
+{
+ struct ramfs_sb_info *rsb = RAMFS_SB(sb);
+
+ lock_rsb(rsb);
+ rsb->free_inodes++;
+ unlock_rsb(rsb);
+}
+
+/* Decrements the free dentry count and returns true, or returns false
+ * if there are no free dentries */
+static int ramfs_alloc_dentry(struct super_block *sb)
+{
+ struct ramfs_sb_info *rsb = RAMFS_SB(sb);
+ int ret = 1;
+
+ lock_rsb(rsb);
+ if (!rsb->max_dentries || rsb->free_dentries > 0)
+ rsb->free_dentries--;
+ else
+ ret = 0;
+ unlock_rsb(rsb);
+
+ return ret;
+}
+
+/* Increments the free dentry count */
+static void ramfs_dealloc_dentry(struct super_block *sb)
+{
+ struct ramfs_sb_info *rsb = RAMFS_SB(sb);
+
+ lock_rsb(rsb);
+ rsb->free_dentries++;
+ unlock_rsb(rsb);
+}
+
+/* If the given page can be added to the give inode for ramfs, return
+ * true and update the filesystem's free page count and the inode's
+ * i_blocks field. Always returns true if the file is already used by
+ * ramfs (ie. PageDirty(page) is true) */
+int ramfs_alloc_page(struct inode *inode, struct page *page)
+{
+ struct ramfs_sb_info *rsb = RAMFS_SB(inode->i_sb);
+ int ret = 1;
+
+ if (PageDirty(page)) /* It's already been allocated */
+ return 1;
+
+ lock_rsb(rsb);
+
+ if ( (rsb->free_pages > 0) &&
+ ( !rsb->max_file_pages ||
+ (inode->i_data.nrpages <= rsb->max_file_pages) ) ) {
+ inode->i_blocks += IBLOCKS_PER_PAGE;
+ rsb->free_pages--;
+ SetPageDirty(page);
+ } else {
+ ClearPageUptodate(page);
+ ret = 0;
+ }
+
+ unlock_rsb(rsb);
+
+ return ret;
+}
+
+void ramfs_dealloc_page(struct inode *inode, struct page *page)
+{
+ struct ramfs_sb_info *rsb = RAMFS_SB(inode->i_sb);
+
+ if (! PageDirty(page)) /* The page was never allocated
+ this can happen if it was only read */
+ return;
+
+ lock_rsb(rsb);
+
+ ClearPageDirty(page);
+
+ rsb->free_pages++;
+ inode->i_blocks -= IBLOCKS_PER_PAGE;
+
+ if (rsb->free_pages > rsb->max_pages) {
+ printk(KERN_ERR "ramfs: Error in page allocation, free_pages (%ld) > max_pages (%ld)\n", rsb->free_pages, rsb->max_pages);
+ }
+
+ unlock_rsb(rsb);
+}
+
+
+
static int ramfs_statfs(struct super_block *sb, struct statfs *buf)
{
+ struct ramfs_sb_info *rsb = RAMFS_SB(sb);
+
+ lock_rsb(rsb);
+ buf->f_blocks = rsb->max_pages;
+ buf->f_files = rsb->max_inodes;
+
+ buf->f_bfree = rsb->free_pages;
+ buf->f_bavail = buf->f_bfree;
+ buf->f_ffree = rsb->free_inodes;
+ unlock_rsb(rsb);
+
buf->f_type = RAMFS_MAGIC;
buf->f_bsize = PAGE_CACHE_SIZE;
buf->f_namelen = 255;
@@ -80,19 +259,29 @@
*/
static int ramfs_writepage(struct file *file, struct page *page)
{
- SetPageDirty(page);
+ struct inode *inode = (struct inode *)page->mapping->host;
+
+ if (! ramfs_alloc_page(inode, page))
+ return -ENOSPC;
+
return 0;
}

static int ramfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
- void *addr = kmap(page);
+ struct inode *inode = (struct inode *)page->mapping->host;
+ void *addr;
+
+ if (! ramfs_alloc_page(inode, page)) {
+ return -ENOSPC;
+ }
+
+ addr = (void *) kmap(page);
if (!Page_Uptodate(page)) {
memset(addr, 0, PAGE_CACHE_SIZE);
flush_dcache_page(page);
SetPageUptodate(page);
}
- SetPageDirty(page);
return 0;
}

@@ -107,9 +296,21 @@
return 0;
}

+static void ramfs_truncatepage(struct page *page)
+{
+ struct inode *inode = (struct inode *)page->mapping->host;
+
+ ramfs_dealloc_page(inode, page);
+}
+
struct inode *ramfs_get_inode(struct super_block *sb, int mode, int dev)
{
- struct inode * inode = new_inode(sb);
+ struct inode * inode;
+
+ if (! ramfs_alloc_inode(sb))
+ return NULL;
+
+ inode = new_inode(sb);

if (inode) {
inode->i_mode = mode;
@@ -135,23 +336,35 @@
inode->i_op = &page_symlink_inode_operations;
break;
}
- }
+ } else
+ ramfs_dealloc_inode(sb);
+
return inode;
}

/*
- * File creation. Allocate an inode, and we're done..
+ * File creation. Allocate an inode, update free inode and dentry counts
+ * and we're done..
*/
static int ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, int dev)
{
- struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
+ struct super_block *sb = dir->i_sb;
+ struct inode * inode;
int error = -ENOSPC;

+ if (! ramfs_alloc_dentry(sb))
+ return error;
+
+ inode = ramfs_get_inode(dir->i_sb, mode, dev);
+
if (inode) {
d_instantiate(dentry, inode);
dget(dentry); /* Extra count - pin the dentry in core */
error = 0;
+ } else {
+ ramfs_dealloc_dentry(sb);
}
+
return error;
}

@@ -170,11 +383,15 @@
*/
static int ramfs_link(struct dentry *old_dentry, struct inode * dir, struct dentry * dentry)
{
+ struct super_block *sb = dir->i_sb;
struct inode *inode = old_dentry->d_inode;

if (S_ISDIR(inode->i_mode))
return -EPERM;

+ if (! ramfs_alloc_dentry(sb))
+ return -ENOSPC;
+
inode->i_nlink++;
atomic_inc(&inode->i_count); /* New dentry reference */
dget(dentry); /* Extra pinning count for the created dentry */
@@ -221,6 +438,7 @@
*/
static int ramfs_unlink(struct inode * dir, struct dentry *dentry)
{
+ struct super_block *sb = dir->i_sb;
int retval = -ENOTEMPTY;

if (ramfs_empty(dentry)) {
@@ -228,6 +446,9 @@

inode->i_nlink--;
dput(dentry); /* Undo the count from "create" - this does all the work */
+
+ ramfs_dealloc_dentry(sb);
+
retval = 0;
}
return retval;
@@ -243,6 +464,8 @@
*/
static int ramfs_rename(struct inode * old_dir, struct dentry *old_dentry, struct inode * new_dir,struct dentry *new_dentry)
{
+ struct super_block *sb = new_dir->i_sb;
+
int error = -ENOTEMPTY;

if (ramfs_empty(new_dentry)) {
@@ -250,6 +473,7 @@
if (inode) {
inode->i_nlink--;
dput(new_dentry);
+ ramfs_dealloc_dentry(sb);
}
error = 0;
}
@@ -269,11 +493,175 @@
return error;
}

+static void ramfs_delete_inode(struct inode *inode)
+{
+ ramfs_dealloc_inode(inode->i_sb);
+
+ clear_inode(inode);
+}
+
+static void ramfs_put_super(struct super_block *sb)
+{
+ kfree(sb->u.generic_sbp);
+}
+
+struct ramfs_params {
+ long pages;
+ long filepages;
+ long inodes;
+ long dentries;
+};
+
+static int parse_options(char * options, struct ramfs_params *p)
+{
+ char save = 0, *savep = NULL, *optname, *value;
+
+ p->pages = -1;
+ p->filepages = -1;
+ p->inodes = -1;
+ p->dentries = -1;
+
+ for (optname = strtok(options,","); optname;
+ optname = strtok(NULL,",")) {
+ if ((value = strchr(optname,'=')) != NULL) {
+ save = *value;
+ savep = value;
+ *value++ = 0;
+ }
+
+ if (!strcmp(optname, "maxfilesize") && value) {
+ p->filepages = simple_strtoul(value, &value, 0)
+ / K_PER_PAGE;
+ if (*value)
+ return -EINVAL;
+ } else if (!strcmp(optname, "maxsize") && value) {
+ p->pages = simple_strtoul(value, &value, 0)
+ / K_PER_PAGE;
+ if (*value)
+ return -EINVAL;
+ } else if (!strcmp(optname, "maxinodes") && value) {
+ p->inodes = simple_strtoul(value, &value, 0);
+ if (*value)
+ return -EINVAL;
+ } else if (!strcmp(optname, "maxdentries") && value) {
+ p->dentries = simple_strtoul(value, &value, 0);
+ if (*value)
+ return -EINVAL;
+ }
+
+ if (optname != options)
+ *(optname-1) = ',';
+ if (value)
+ *savep = save;
+/* if (ret == 0) */
+/* break; */
+ }
+
+ return 0;
+}
+
+static void init_limits(struct ramfs_sb_info *rsb, struct ramfs_params *p)
+{
+ struct sysinfo si;
+
+ si_meminfo(&si);
+
+ /* By default we set the limits to be:
+ - Allow this ramfs to take up to half of all available RAM
+ - No limit on filesize (except no file may be bigger that
+ the total max size, obviously)
+ - dentries limited to one per 4k of data space
+ - No limit to the number of inodes (except that there
+ are never more inodes than dentries).
+ */
+ rsb->max_pages = (si.totalram / 2);
+
+ if (p->pages >= 0)
+ rsb->max_pages = p->pages;
+
+ rsb->max_file_pages = 0;
+ if (p->filepages >= 0)
+ rsb->max_file_pages = p->filepages;
+
+ rsb->max_dentries = rsb->max_pages * K_PER_PAGE / 4;
+ if (p->dentries >= 0)
+ rsb->max_dentries = p->dentries;
+
+ rsb->max_inodes = 0;
+ if (p->inodes >= 0)
+ rsb->max_inodes = p->inodes;
+
+ rsb->free_pages = rsb->max_pages;
+ rsb->free_inodes = rsb->max_inodes;
+ rsb->free_dentries = rsb->max_dentries;
+
+ return;
+}
+
+/* reset_limits is called during a remount to change the usage limits.
+
+ This will suceed, even if the new limits are lower than current
+ usage. This is the intended behaviour - new allocations will fail
+ until usage falls below the new limit */
+static void reset_limits(struct ramfs_sb_info *rsb, struct ramfs_params *p)
+{
+ lock_rsb(rsb);
+
+ if (p->pages >= 0) {
+ int used_pages = rsb->max_pages - rsb->free_pages;
+
+ rsb->max_pages = p->pages;
+ rsb->free_pages = rsb->max_pages - used_pages;
+ }
+
+ if (p->filepages >= 0) {
+ rsb->max_file_pages = p->filepages;
+ }
+
+
+ if (p->dentries >= 0) {
+ int used_dentries = rsb->max_dentries - rsb->free_dentries;
+
+ rsb->max_dentries = p->dentries;
+ rsb->free_dentries = rsb->max_dentries - used_dentries;
+ }
+
+ if (p->inodes >= 0) {
+ int used_inodes = rsb->max_inodes - rsb->free_inodes;
+
+ rsb->max_inodes = p->inodes;
+ rsb->free_inodes = rsb->max_inodes - used_inodes;
+ }
+
+ unlock_rsb(rsb);
+}
+
+static int ramfs_remount(struct super_block * sb, int * flags, char * data)
+{
+ struct ramfs_params params;
+ struct ramfs_sb_info * rsb = RAMFS_SB(sb);
+
+ if (parse_options((char *)data, &params) != 0)
+ return -EINVAL;
+
+ reset_limits(rsb, &params);
+
+ printk(KERN_DEBUG "ramfs: remounted with options: %s\n",
+ data ? (char *)data : "<defaults>" );
+ printk(KERN_DEBUG "ramfs: max_pages=%ld max_file_pages=%ld \
+max_inodes=%ld max_dentries=%ld\n",
+ rsb->max_pages, rsb->max_file_pages,
+ rsb->max_inodes, rsb->max_dentries);
+
+ return 0;
+}
+
static struct address_space_operations ramfs_aops = {
readpage: ramfs_readpage,
writepage: ramfs_writepage,
prepare_write: ramfs_prepare_write,
- commit_write: ramfs_commit_write
+ commit_write: ramfs_commit_write,
+ truncatepage: ramfs_truncatepage,
};

static struct file_operations ramfs_file_operations = {
@@ -302,17 +690,37 @@
static struct super_operations ramfs_ops = {
statfs: ramfs_statfs,
put_inode: force_delete,
+ delete_inode: ramfs_delete_inode,
+ put_super: ramfs_put_super,
+ remount_fs: ramfs_remount,
};

+/*
+ * Initialisation
+ */
+
static struct super_block *ramfs_read_super(struct super_block * sb, void * data, int silent)
{
struct inode * inode;
struct dentry * root;
+ struct ramfs_sb_info * rsb;
+ struct ramfs_params params;

sb->s_blocksize = PAGE_CACHE_SIZE;
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
sb->s_magic = RAMFS_MAGIC;
sb->s_op = &ramfs_ops;
+
+ sb->u.generic_sbp = kmalloc(sizeof(struct ramfs_sb_info), GFP_KERNEL);
+ rsb = RAMFS_SB(sb);
+
+ spin_lock_init(&rsb->ramfs_lock);
+
+ if (parse_options((char *)data, &params) != 0)
+ return NULL;
+
+ init_limits(rsb, &params);
+
inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0);
if (!inode)
return NULL;
@@ -323,6 +731,13 @@
return NULL;
}
sb->s_root = root;
+
+ printk(KERN_DEBUG "ramfs: mounted with options: %s\n",
+ data ? (char *)data : "<defaults>" );
+ printk(KERN_DEBUG "ramfs: max_pages=%ld max_file_pages=%ld \
+max_inodes=%ld max_dentries=%ld\n",
+ rsb->max_pages, rsb->max_file_pages,
+ rsb->max_inodes, rsb->max_dentries);
return sb;
}

diff -uNr test11/include/linux/fs.h test11-ramfs/include/linux/fs.h
--- test11/include/linux/fs.h Mon Nov 20 14:05:37 2000
+++ test11-ramfs/include/linux/fs.h Tue Nov 21 17:29:36 2000
@@ -354,6 +354,7 @@
int (*sync_page)(struct page *);
int (*prepare_write)(struct file *, struct page *, unsigned, unsigned);
int (*commit_write)(struct file *, struct page *, unsigned, unsigned);
+ void (*truncatepage)(struct page *); /* called from truncate_complete_page */
/* Unfortunately this kludge is needed for FIBMAP. Don't use it */
int (*bmap)(struct address_space *, long);
};
diff -uNr test11/mm/filemap.c test11-ramfs/mm/filemap.c
--- test11/mm/filemap.c Mon Nov 20 14:05:38 2000
+++ test11-ramfs/mm/filemap.c Tue Nov 21 17:29:21 2000
@@ -166,6 +166,9 @@
if (!page->buffers || block_flushpage(page, 0))
lru_cache_del(page);

+ if (page->mapping->a_ops->truncatepage)
+ page->mapping->a_ops->truncatepage(page);
+
/*
* We remove the page from the page cache _after_ we have
* destroyed all buffer-cache references to it. Otherwise some
-
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