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Stop playing silly games with the VM_ACCOUNT flag

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The mmap_region() code would temporarily set the VM_ACCOUNT flag for
anonymous shared mappings just to inform shmem_zero_setup() that it
should enable accounting for the resulting shm object.  It would then
clear the flag after calling ->mmap (for the /dev/zero case) or doing
shmem_zero_setup() (for the MAP_ANON case).

This just resulted in vma merge issues, but also made for just
unnecessary confusion.  Use the already-existing VM_NORESERVE flag for
this instead, and let shmem_{zero|file}_setup() just figure it out from
that.

This also happens to make it obvious that the new DRI2 GEM layer uses a
non-reserving backing store for its object allocation - which is quite
possibly not intentional.  But since I didn't want to change semantics
in this patch, I left it alone, and just updated the caller to use the
new flag semantics.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2009-01-31 15:08:56 -08:00
parent 33bfad54b5
commit fc8744adc8
4 changed files with 29 additions and 27 deletions
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2
drivers/gpu/drm/drm_gem.c
View File

@ -136,7 +136,7 @@ drm_gem_object_alloc(struct drm_device *dev, size_t size)
obj = kcalloc(1, sizeof(*obj), GFP_KERNEL);
obj->dev = dev;
obj->filp = shmem_file_setup("drm mm object", size, 0);
obj->filp = shmem_file_setup("drm mm object", size, VM_NORESERVE);
if (IS_ERR(obj->filp)) {
kfree(obj);
return NULL;

4
ipc/shm.c
View File

@ -368,14 +368,14 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
file = hugetlb_file_setup(name, size);
shp->mlock_user = current_user();
} else {
int acctflag = VM_ACCOUNT;
int acctflag = 0;
/*
* Do not allow no accounting for OVERCOMMIT_NEVER, even
* if it's asked for.
*/
if ((shmflg & SHM_NORESERVE) &&
sysctl_overcommit_memory != OVERCOMMIT_NEVER)
acctflag = 0;
acctflag = VM_NORESERVE;
file = shmem_file_setup(name, size, acctflag);
}
error = PTR_ERR(file);

34
mm/mmap.c
View File

@ -1090,6 +1090,15 @@ int vma_wants_writenotify(struct vm_area_struct *vma)
mapping_cap_account_dirty(vma->vm_file->f_mapping);
}
/*
* We account for memory if it's a private writeable mapping,
* and VM_NORESERVE wasn't set.
*/
static inline int accountable_mapping(unsigned int vm_flags)
{
return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
}
unsigned long mmap_region(struct file *file, unsigned long addr,
unsigned long len, unsigned long flags,
unsigned int vm_flags, unsigned long pgoff,
@ -1117,24 +1126,25 @@ munmap_back:
if (!may_expand_vm(mm, len >> PAGE_SHIFT))
return -ENOMEM;
if (flags & MAP_NORESERVE)
/*
* Set 'VM_NORESERVE' if we should not account for the
* memory use of this mapping. We only honor MAP_NORESERVE
* if we're allowed to overcommit memory.
*/
if ((flags & MAP_NORESERVE) && sysctl_overcommit_memory != OVERCOMMIT_NEVER)
vm_flags |= VM_NORESERVE;
if (!accountable)
vm_flags |= VM_NORESERVE;
if (accountable && (!(flags & MAP_NORESERVE) ||
sysctl_overcommit_memory == OVERCOMMIT_NEVER)) {
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
*/
if (accountable_mapping(vm_flags)) {
charged = len >> PAGE_SHIFT;
if (security_vm_enough_memory(charged))
return -ENOMEM;
vm_flags |= VM_ACCOUNT;
}
}
/*
* Can we just expand an old mapping?
@ -1184,14 +1194,6 @@ munmap_back:
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??
*
* Answer: Yes, several device drivers can do it in their

2
mm/shmem.c
View File

@ -2628,7 +2628,7 @@ struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
goto close_file;
#ifdef CONFIG_SHMEM
SHMEM_I(inode)->flags = flags & VM_ACCOUNT;
SHMEM_I(inode)->flags = (flags & VM_NORESERVE) ? 0 : VM_ACCOUNT;
#endif
d_instantiate(dentry, inode);
inode->i_size = size;