Commit 77142517 authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Linus Torvalds

shmem: update memory reservation on truncate

A shared anonymous mapping created without MAP_NORESERVE holds memory
reservation for whole range of shmem segment.  Usually there is no way
to change its size, but /proc/<pid>/map_files/...  (available if

This patch adjusts the memory reservation in shmem_setattr().
Signed-off-by: default avatarKonstantin Khlebnikov <>
Acked-by: default avatarHugh Dickins <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 66ee4b88
......@@ -149,6 +149,19 @@ static inline void shmem_unacct_size(unsigned long flags, loff_t size)
static inline int shmem_reacct_size(unsigned long flags,
loff_t oldsize, loff_t newsize)
if (!(flags & VM_NORESERVE)) {
if (VM_ACCT(newsize) > VM_ACCT(oldsize))
return security_vm_enough_memory_mm(current->mm,
VM_ACCT(newsize) - VM_ACCT(oldsize));
else if (VM_ACCT(newsize) < VM_ACCT(oldsize))
vm_unacct_memory(VM_ACCT(oldsize) - VM_ACCT(newsize));
return 0;
* ... whereas tmpfs objects are accounted incrementally as
* pages are allocated, in order to allow huge sparse files.
......@@ -549,6 +562,10 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
loff_t newsize = attr->ia_size;
if (newsize != oldsize) {
error = shmem_reacct_size(SHMEM_I(inode)->flags,
oldsize, newsize);
if (error)
return error;
i_size_write(inode, newsize);
inode->i_ctime = inode->i_mtime = CURRENT_TIME;
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