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Message-ID: <aRrvaHh-cP8jygAF@kernel.org>
Date: Mon, 17 Nov 2025 11:48:24 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
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Subject: Re: [PATCH v6 11/20] mm: shmem: use SHMEM_F_* flags instead of VM_*
flags
On Sat, Nov 15, 2025 at 06:33:57PM -0500, Pasha Tatashin wrote:
> From: Pratyush Yadav <ptyadav@...zon.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@...zon.de>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.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.
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