From: Hugh Dickins <hugh@veritas.com>
Kevin P. Fleming pointed out that the 2.6 tmpfs does not allow writing huge
sparse files. This is an unintended side-effect of the strict memory commit
changes: which should make no
The solution is to treat the tmpfs files (of variable size) and the shmem
objects (of fixed size) differently: sounds nasty but works out well. The
shmem objects follow the VM preallocation convention as before, but the tmpfs
files revert to allocation on demand as a filesystem would. If there's not
enough memory to write to a tmpfs hole, it is reported as -ENOSPC rather than
-ENOMEM, so the mmap writer gets SIGBUS rather than everyone else getting
OOM-killed.
---
25-akpm/mm/shmem.c | 95 +++++++++++++++++++++++++++--------------------------
1 files changed, 50 insertions(+), 45 deletions(-)
diff -puN mm/shmem.c~huge-sparse-tmpfs-files mm/shmem.c
--- 25/mm/shmem.c~huge-sparse-tmpfs-files 2004-04-03 03:00:05.811348096 -0800
+++ 25-akpm/mm/shmem.c 2004-04-03 03:00:05.817347184 -0800
@@ -123,6 +123,42 @@ static inline struct shmem_sb_info *SHME
return sb->s_fs_info;
}
+/*
+ * shmem_file_setup pre-accounts the whole fixed size of a VM object,
+ * for shared memory and for shared anonymous (/dev/zero) mappings
+ * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
+ * consistent with the pre-accounting of private mappings ...
+ */
+static inline int shmem_acct_size(unsigned long flags, loff_t size)
+{
+ return (flags & VM_ACCOUNT)?
+ security_vm_enough_memory(VM_ACCT(size)): 0;
+}
+
+static inline void shmem_unacct_size(unsigned long flags, loff_t size)
+{
+ if (flags & VM_ACCOUNT)
+ vm_unacct_memory(VM_ACCT(size));
+}
+
+/*
+ * ... whereas tmpfs objects are accounted incrementally as
+ * pages are allocated, in order to allow huge sparse files.
+ * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
+ * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
+ */
+static inline int shmem_acct_block(unsigned long flags)
+{
+ return (flags & VM_ACCOUNT)?
+ 0: security_vm_enough_memory(VM_ACCT(PAGE_CACHE_SIZE));
+}
+
+static inline void shmem_unacct_blocks(unsigned long flags, long pages)
+{
+ if (!(flags & VM_ACCOUNT))
+ vm_unacct_memory(pages * VM_ACCT(PAGE_CACHE_SIZE));
+}
+
static struct super_operations shmem_ops;
static struct address_space_operations shmem_aops;
static struct file_operations shmem_file_operations;
@@ -173,6 +209,7 @@ static void shmem_recalc_inode(struct in
sbinfo->free_blocks += freed;
inode->i_blocks -= freed*BLOCKS_PER_PAGE;
spin_unlock(&sbinfo->stat_lock);
+ shmem_unacct_blocks(info->flags, freed);
}
}
@@ -456,7 +493,7 @@ static void shmem_truncate(struct inode
shmem_dir_unmap(dir);
if (empty) {
shmem_dir_free(empty);
- info->alloced++;
+ shmem_free_block(inode);
}
empty = subdir;
cond_resched_lock(&info->lock);
@@ -479,19 +516,19 @@ static void shmem_truncate(struct inode
else if (subdir) {
*dir = NULL;
shmem_dir_free(subdir);
- info->alloced++;
+ shmem_free_block(inode);
}
}
done1:
shmem_dir_unmap(dir-1);
if (empty) {
shmem_dir_free(empty);
- info->alloced++;
+ shmem_free_block(inode);
}
if (info->next_index <= SHMEM_NR_DIRECT) {
shmem_dir_free(info->i_indirect);
info->i_indirect = NULL;
- info->alloced++;
+ shmem_free_block(inode);
}
done2:
BUG_ON(info->swapped > info->next_index);
@@ -516,20 +553,10 @@ static int shmem_notify_change(struct de
{
struct inode *inode = dentry->d_inode;
struct page *page = NULL;
- long change = 0;
int error;
- if ((attr->ia_valid & ATTR_SIZE) && (attr->ia_size <= SHMEM_MAX_BYTES)) {
- /*
- * Account swap file usage based on new file size,
- * but just let vmtruncate fail on out-of-range sizes.
- */
- change = VM_ACCT(attr->ia_size) - VM_ACCT(inode->i_size);
- if (change > 0) {
- if (security_vm_enough_memory(change))
- return -ENOMEM;
- } else if (attr->ia_size < inode->i_size) {
- vm_unacct_memory(-change);
+ if (attr->ia_valid & ATTR_SIZE) {
+ if (attr->ia_size < inode->i_size) {
/*
* If truncating down to a partial page, then
* if that page is already allocated, hold it
@@ -563,8 +590,6 @@ static int shmem_notify_change(struct de
error = inode_setattr(inode, attr);
if (page)
page_cache_release(page);
- if (error)
- vm_unacct_memory(change);
return error;
}
@@ -577,8 +602,7 @@ static void shmem_delete_inode(struct in
spin_lock(&shmem_ilock);
list_del(&info->list);
spin_unlock(&shmem_ilock);
- if (info->flags & VM_ACCOUNT)
- vm_unacct_memory(VM_ACCT(inode->i_size));
+ shmem_unacct_size(info->flags, inode->i_size);
inode->i_size = 0;
shmem_truncate(inode);
}
@@ -909,7 +933,7 @@ repeat:
shmem_swp_unmap(entry);
sbinfo = SHMEM_SB(inode->i_sb);
spin_lock(&sbinfo->stat_lock);
- if (sbinfo->free_blocks == 0) {
+ if (sbinfo->free_blocks == 0 || shmem_acct_block(info->flags)) {
spin_unlock(&sbinfo->stat_lock);
spin_unlock(&info->lock);
error = -ENOSPC;
@@ -923,6 +947,7 @@ repeat:
spin_unlock(&info->lock);
filepage = page_cache_alloc(mapping);
if (!filepage) {
+ shmem_unacct_blocks(info->flags, 1);
shmem_free_block(inode);
error = -ENOMEM;
goto failed;
@@ -940,6 +965,7 @@ repeat:
filepage, mapping, idx, GFP_ATOMIC)) {
spin_unlock(&info->lock);
page_cache_release(filepage);
+ shmem_unacct_blocks(info->flags, 1);
shmem_free_block(inode);
filepage = NULL;
if (error)
@@ -1094,7 +1120,6 @@ shmem_get_inode(struct super_block *sb,
info = SHMEM_I(inode);
memset(info, 0, (char *)inode - (char *)info);
spin_lock_init(&info->lock);
- info->flags = VM_ACCOUNT;
switch (mode & S_IFMT) {
default:
init_special_inode(inode, mode, dev);
@@ -1167,7 +1192,6 @@ shmem_file_write(struct file *file, cons
loff_t pos;
unsigned long written;
int err;
- loff_t maxpos;
if ((ssize_t) count < 0)
return -EINVAL;
@@ -1184,15 +1208,6 @@ shmem_file_write(struct file *file, cons
if (err || !count)
goto out;
- maxpos = inode->i_size;
- if (maxpos < pos + count) {
- maxpos = pos + count;
- if (security_vm_enough_memory(VM_ACCT(maxpos) - VM_ACCT(inode->i_size))) {
- err = -ENOMEM;
- goto out;
- }
- }
-
err = remove_suid(file->f_dentry);
if (err)
goto out;
@@ -1267,10 +1282,6 @@ shmem_file_write(struct file *file, cons
*ppos = pos;
if (written)
err = written;
-
- /* Short writes give back address space */
- if (inode->i_size != maxpos)
- vm_unacct_memory(VM_ACCT(maxpos) - VM_ACCT(inode->i_size));
out:
up(&inode->i_sem);
return err;
@@ -1551,13 +1562,8 @@ static int shmem_symlink(struct inode *d
memcpy(info, symname, len);
inode->i_op = &shmem_symlink_inline_operations;
} else {
- if (security_vm_enough_memory(VM_ACCT(1))) {
- iput(inode);
- return -ENOMEM;
- }
error = shmem_getpage(inode, 0, &page, SGP_WRITE, NULL);
if (error) {
- vm_unacct_memory(VM_ACCT(1));
iput(inode);
return error;
}
@@ -1947,7 +1953,7 @@ struct file *shmem_file_setup(char *name
if (size > SHMEM_MAX_BYTES)
return ERR_PTR(-EINVAL);
- if ((flags & VM_ACCOUNT) && security_vm_enough_memory(VM_ACCT(size)))
+ if (shmem_acct_size(flags, size))
return ERR_PTR(-ENOMEM);
error = -ENOMEM;
@@ -1969,7 +1975,7 @@ struct file *shmem_file_setup(char *name
if (!inode)
goto close_file;
- SHMEM_I(inode)->flags &= flags;
+ SHMEM_I(inode)->flags = flags & VM_ACCOUNT;
d_instantiate(dentry, inode);
inode->i_size = size;
inode->i_nlink = 0; /* It is unlinked */
@@ -1985,8 +1991,7 @@ close_file:
put_dentry:
dput(dentry);
put_memory:
- if (flags & VM_ACCOUNT)
- vm_unacct_memory(VM_ACCT(size));
+ shmem_unacct_size(flags, size);
return ERR_PTR(error);
}
_