Re: [PATCH v6 11/20] mm: shmem: use SHMEM_F_* flags instead of VM_* flags

[Mike Rapoport <rppt@kernel.org>]

On Sat, Nov 15, 2025 at 06:33:57PM -0500, Pasha Tatashin wrote:
> 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>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  include/linux/shmem_fs.h |  6 ++++++
>  mm/shmem.c               | 28 +++++++++++++++-------------
>  2 files changed, 21 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index 0e47465ef0fd..650874b400b5 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 58701d14dd96..1d5036dec08a 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));
>  }
>  
> @@ -1551,7 +1551,7 @@ 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)
> @@ -2910,15 +2910,15 @@ 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;
> @@ -3062,7 +3062,7 @@ 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;
> +	info->flags = (flags & VM_NORESERVE) ? SHMEM_F_NORESERVE : 0;
>  	info->i_crtime = inode_get_mtime(inode);
>  	info->fsflags = (dir == NULL) ? 0 :
>  		SHMEM_I(dir)->fsflags & SHMEM_FL_INHERITED;
> @@ -5804,8 +5804,10 @@ 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;
>  
> @@ -5822,7 +5824,7 @@ 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);
> -- 
> 2.52.0.rc1.455.g30608eb744-goog
> 

-- 
Sincerely yours,
Mike.