[PATCH v5 13/22] mm: shmem: use SHMEM_F_* flags instead of VM_* flags

Pasha Tatashin
2025-11-07T21:05:58Z

From: Pratyush Yadav <ptyadav@amazon.de>

shmem_inode_info::flags can have the VM flags VM_NORESERVE and
VM_LOCKED. These are used to suppress pre-accounting or to lock the
pages in the inode respectively. Using the VM flags directly makes it
difficult to add shmem-specific flags that are unrelated to VM behavior
since one would need to find a VM flag not used by shmem and re-purpose
it.

Introduce SHMEM_F_NORESERVE and SHMEM_F_LOCKED which represent the same
information, but their bits are independent of the VM flags. Callers can
still pass VM_NORESERVE to shmem_get_inode(), but it gets transformed to
the shmem-specific flag internally.

No functional changes intended.

Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
include/linux/shmem_fs.h | 6 ++++++
mm/shmem.c | 29 ++++++++++++++++-------------
2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 5b368f9549d6..710b1dd681bf 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -10,6 +10,7 @@
#include <linux/xattr.h>
#include <linux/fs_parser.h>
#include <linux/userfaultfd_k.h>
+#include <linux/bits.h>

struct swap_iocb;

@@ -19,6 +20,11 @@ struct swap_iocb;
#define SHMEM_MAXQUOTAS 2
#endif

+/* Suppress pre-accounting of the entire object size. */
+#define SHMEM_F_NORESERVE BIT(0)
+/* Disallow swapping. */
+#define SHMEM_F_LOCKED BIT(1)
+
struct shmem_inode_info {
spinlock_t lock;
unsigned int seals; /* shmem seals */
diff --git a/mm/shmem.c b/mm/shmem.c
index 5c07e2b57c34..19be8c575647 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -175,20 +175,20 @@ static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
*/
static inline int shmem_acct_size(unsigned long flags, loff_t size)
{
- return (flags & VM_NORESERVE) ?
+ return (flags & SHMEM_F_NORESERVE) ?
0 : security_vm_enough_memory_mm(current->mm, VM_ACCT(size));
}

static inline void shmem_unacct_size(unsigned long flags, loff_t size)
{
- if (!(flags & VM_NORESERVE))
+ if (!(flags & SHMEM_F_NORESERVE))
vm_unacct_memory(VM_ACCT(size));
}

static inline int shmem_reacct_size(unsigned long flags,
loff_t oldsize, loff_t newsize)
{
- if (!(flags & VM_NORESERVE)) {
+ if (!(flags & SHMEM_F_NORESERVE)) {
if (VM_ACCT(newsize) > VM_ACCT(oldsize))
return security_vm_enough_memory_mm(current->mm,
VM_ACCT(newsize) - VM_ACCT(oldsize));
@@ -206,7 +206,7 @@ static inline int shmem_reacct_size(unsigned long flags,
*/
static inline int shmem_acct_blocks(unsigned long flags, long pages)
{
- if (!(flags & VM_NORESERVE))
+ if (!(flags & SHMEM_F_NORESERVE))
return 0;

return security_vm_enough_memory_mm(current->mm,
@@ -215,7 +215,7 @@ static inline int shmem_acct_blocks(unsigned long flags, long pages)

static inline void shmem_unacct_blocks(unsigned long flags, long pages)
{
- if (flags & VM_NORESERVE)
+ if (flags & SHMEM_F_NORESERVE)
vm_unacct_memory(pages * VM_ACCT(PAGE_SIZE));
}

@@ -1580,7 +1580,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
int nr_pages;
bool split = false;

- if ((info->flags & VM_LOCKED) || sbinfo->noswap)
+ if ((info->flags & SHMEM_F_LOCKED) || sbinfo->noswap)
goto redirty;

if (!total_swap_pages)
@@ -2938,15 +2938,15 @@ int shmem_lock(struct file *file, int lock, struct ucounts *ucounts)
* ipc_lock_object() when called from shmctl_do_lock(),
* no serialization needed when called from shm_destroy().
*/
- if (lock && !(info->flags & VM_LOCKED)) {
+ if (lock && !(info->flags & SHMEM_F_LOCKED)) {
if (!user_shm_lock(inode->i_size, ucounts))
goto out_nomem;
- info->flags |= VM_LOCKED;
+ info->flags |= SHMEM_F_LOCKED;
mapping_set_unevictable(file->f_mapping);
}
- if (!lock && (info->flags & VM_LOCKED) && ucounts) {
+ if (!lock && (info->flags & SHMEM_F_LOCKED) && ucounts) {
user_shm_unlock(inode->i_size, ucounts);
- info->flags &= ~VM_LOCKED;
+ info->flags &= ~SHMEM_F_LOCKED;
mapping_clear_unevictable(file->f_mapping);
}
retval = 0;
@@ -3091,7 +3091,8 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
spin_lock_init(&info->lock);
atomic_set(&info->stop_eviction, 0);
info->seals = F_SEAL_SEAL;
- info->flags = flags & VM_NORESERVE;
+ if (flags & VM_NORESERVE)
+ info->flags = SHMEM_F_NORESERVE;
info->i_crtime = inode_get_mtime(inode);
info->fsflags = (dir == NULL) ? 0 :
SHMEM_I(dir)->fsflags & SHMEM_FL_INHERITED;
@@ -5833,8 +5834,10 @@ static inline struct inode *shmem_get_inode(struct mnt_idmap *idmap,
/* common code */

static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name,
- loff_t size, unsigned long flags, unsigned int i_flags)
+ loff_t size, unsigned long vm_flags,
+ unsigned int i_flags)
{
+ unsigned long flags = (vm_flags & VM_NORESERVE) ? SHMEM_F_NORESERVE : 0;
struct inode *inode;
struct file *res;

@@ -5851,7 +5854,7 @@ static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name,
return ERR_PTR(-ENOMEM);

inode = shmem_get_inode(&nop_mnt_idmap, mnt->mnt_sb, NULL,
- S_IFREG | S_IRWXUGO, 0, flags);
+ S_IFREG | S_IRWXUGO, 0, vm_flags);
if (IS_ERR(inode)) {
shmem_unacct_size(flags, size);
return ERR_CAST(inode);
--
2.51.2.1041.gc1ab5b90ca-goog