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Subject[PATCH] vmacct8/9 shmem_file_setup when MAP_NORESERVE
Tangential to VM overcommit strict accounting,
On Fri, 12 Jul 2002, David Mosberger wrote to LKML:
> Is there a good reason why the MAP_NORESERVE flag is ignored when
> MAP_SHARED is specified? (Hint: it's the call to vm_enough_memory()
> in shmem_file_setup() that's causing MAP_NORESERVE to be ignored.)

He's right, if we support mmap MAP_NORESERVE, we should support
it on shared anonymous objects: too bad that needs a few changes.
do_mmap_pgoff pass VM_ACCOUNT (or not) down to shmem_file_setup,
flag stored into shmem info, for use by shmem_delete_inode later.
Also removed a harmless but pointless call to shmem_truncate.

--- vmacct7/include/linux/mm.h Mon Jul 29 11:48:04 2002
+++ vmacct8/include/linux/mm.h Mon Jul 29 19:23:46 2002
@@ -331,7 +331,7 @@

extern int fail_writepage(struct page *);
struct page * shmem_nopage(struct vm_area_struct * vma, unsigned long address, int unused);
-struct file *shmem_file_setup(char * name, loff_t size);
+struct file *shmem_file_setup(char * name, loff_t size, unsigned long flags);
extern void shmem_lock(struct file * file, int lock);
extern int shmem_zero_setup(struct vm_area_struct *);

--- vmacct7/include/linux/shmem_fs.h Thu Jul 25 13:04:59 2002
+++ vmacct8/include/linux/shmem_fs.h Mon Jul 29 19:23:46 2002
@@ -16,7 +16,7 @@
swp_entry_t i_direct[SHMEM_NR_DIRECT]; /* for the first blocks */
void **i_indirect; /* indirect blocks */
unsigned long swapped;
- int locked; /* into memory */
+ unsigned long flags;
struct list_head list;
struct inode vfs_inode;
};
--- vmacct7/ipc/shm.c Mon Jul 29 11:48:04 2002
+++ vmacct8/ipc/shm.c Mon Jul 29 19:23:46 2002
@@ -186,7 +186,7 @@
shp->shm_flags = (shmflg & S_IRWXUGO);

sprintf (name, "SYSV%08x", key);
- file = shmem_file_setup(name, size);
+ file = shmem_file_setup(name, size, VM_ACCOUNT);
error = PTR_ERR(file);
if (IS_ERR(file))
goto no_file;
--- vmacct7/mm/mmap.c Mon Jul 29 19:23:46 2002
+++ vmacct8/mm/mmap.c Mon Jul 29 19:23:46 2002
@@ -528,7 +528,10 @@
return -ENOMEM;

if (!(flags & MAP_NORESERVE) || sysctl_overcommit_memory > 1) {
- if ((vm_flags & (VM_SHARED|VM_WRITE)) == VM_WRITE) {
+ if (vm_flags & VM_SHARED) {
+ /* Check memory availability in shmem_file_setup? */
+ vm_flags |= VM_ACCOUNT;
+ } else if (vm_flags & VM_WRITE) {
/* Private writable mapping: check memory availability */
charged = len >> PAGE_SHIFT;
if (!vm_enough_memory(charged))
@@ -582,6 +585,14 @@
if (error)
goto free_vma;
}
+
+ /* We set VM_ACCOUNT in a shared mapping's vm_flags, to inform
+ * shmem_zero_setup (perhaps called through /dev/zero's ->mmap)
+ * that memory reservation must be checked; but that reservation
+ * belongs to shared memory object, not to vma: so now clear it.
+ */
+ if ((vm_flags & (VM_SHARED|VM_ACCOUNT)) == (VM_SHARED|VM_ACCOUNT))
+ vma->vm_flags &= ~VM_ACCOUNT;

/* Can addr have changed??
*
--- vmacct7/mm/shmem.c Mon Jul 29 19:23:46 2002
+++ vmacct8/mm/shmem.c Mon Jul 29 19:23:46 2002
@@ -392,12 +392,14 @@
static void shmem_delete_inode(struct inode * inode)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
+ struct shmem_inode_info *info = SHMEM_I(inode);

if (inode->i_op->truncate == shmem_truncate) {
- spin_lock (&shmem_ilock);
- list_del (&SHMEM_I(inode)->list);
- spin_unlock (&shmem_ilock);
- vm_unacct_memory(VM_ACCT(inode->i_size));
+ 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));
inode->i_size = 0;
shmem_truncate (inode);
}
@@ -526,7 +528,7 @@
index = page->index;
inode = mapping->host;
info = SHMEM_I(inode);
- if (info->locked)
+ if (info->flags & VM_LOCKED)
return fail_writepage(page);
swap = get_swap_page();
if (!swap.val)
@@ -743,9 +745,12 @@
struct inode * inode = file->f_dentry->d_inode;
struct shmem_inode_info * info = SHMEM_I(inode);

- down(&info->sem);
- info->locked = lock;
- up(&info->sem);
+ spin_lock(&info->lock);
+ if (lock)
+ info->flags |= VM_LOCKED;
+ else
+ info->flags &= ~VM_LOCKED;
+ spin_unlock(&info->lock);
}

static int shmem_mmap(struct file * file, struct vm_area_struct * vma)
@@ -792,7 +797,7 @@
memset (info->i_direct, 0, sizeof(info->i_direct));
info->i_indirect = NULL;
info->swapped = 0;
- info->locked = 0;
+ info->flags = VM_ACCOUNT;
switch (mode & S_IFMT) {
default:
init_special_inode(inode, mode, dev);
@@ -1652,7 +1657,7 @@
* @size: size to be set for the file
*
*/
-struct file *shmem_file_setup(char * name, loff_t size)
+struct file *shmem_file_setup(char * name, loff_t size, unsigned long flags)
{
int error;
struct file *file;
@@ -1663,7 +1668,7 @@
if (size > SHMEM_MAX_BYTES)
return ERR_PTR(-EINVAL);

- if (!vm_enough_memory(VM_ACCT(size)))
+ if ((flags & VM_ACCOUNT) && !vm_enough_memory(VM_ACCT(size)))
return ERR_PTR(-ENOMEM);

error = -ENOMEM;
@@ -1685,14 +1690,14 @@
if (!inode)
goto close_file;

+ SHMEM_I(inode)->flags &= flags;
d_instantiate(dentry, inode);
- dentry->d_inode->i_size = size;
- shmem_truncate(inode);
+ inode->i_size = size;
+ inode->i_nlink = 0; /* It is unlinked */
file->f_vfsmnt = mntget(shm_mnt);
file->f_dentry = dentry;
file->f_op = &shmem_file_operations;
file->f_mode = FMODE_WRITE | FMODE_READ;
- inode->i_nlink = 0; /* It is unlinked */
return(file);

close_file:
@@ -1700,7 +1705,8 @@
put_dentry:
dput (dentry);
put_memory:
- vm_unacct_memory(VM_ACCT(size));
+ if (flags & VM_ACCOUNT)
+ vm_unacct_memory(VM_ACCT(size));
return ERR_PTR(error);
}

@@ -1714,7 +1720,7 @@
struct file *file;
loff_t size = vma->vm_end - vma->vm_start;

- file = shmem_file_setup("dev/zero", size);
+ file = shmem_file_setup("dev/zero", size, vma->vm_flags);
if (IS_ERR(file))
return PTR_ERR(file);

-
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