tmpfs: use kmemdup for short symlinks

But we've not yet removed the old swp_entry_t i_direct[16] from
shmem_inode_info.  That's because it was still being shared with the
inline symlink.  Remove it now (saving 64 or 128 bytes from shmem inode
size), and use kmemdup() for short symlinks, say, those up to 128 bytes.

I wonder why mpol_free_shared_policy() is done in shmem_destroy_inode()
rather than shmem_evict_inode(), where we usually do such freeing? I
guess it doesn't matter, and I'm not into NUMA mpol testing right now.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 13 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 0f094a258526..3a5be0feb6af 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -73,6 +73,9 @@ static struct vfsmount *shm_mnt;
 /* Pretend that each entry is of this size in directory's i_size */
 #define BOGO_DIRENT_SIZE 20
 
+/* Symlink up to this size is kmalloc'ed instead of using a swappable page */
+#define SHORT_SYMLINK_LEN 128
+
 struct shmem_xattr {
         struct list_head list;  /* anchored by shmem_inode_info->xattr_list */
         char *name;             /* xattr name */
@@ -585,7 +588,8 @@ static void shmem_evict_inode(struct inode *inode)
                         list_del_init(&info->swaplist);
                         mutex_unlock(&shmem_swaplist_mutex);
                 }
-        }
+        } else
+                kfree(info->symlink);
 
         list_for_each_entry_safe(xattr, nxattr, &info->xattr_list, list) {
                 kfree(xattr->name);
@@ -1173,7 +1177,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 
 #ifdef CONFIG_TMPFS
 static const struct inode_operations shmem_symlink_inode_operations;
-static const struct inode_operations shmem_symlink_inline_operations;
+static const struct inode_operations shmem_short_symlink_operations;
 
 static int
 shmem_write_begin(struct file *file, struct address_space *mapping,
@@ -1638,10 +1642,13 @@ static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *s
 
         info = SHMEM_I(inode);
         inode->i_size = len-1;
-        if (len <= SHMEM_SYMLINK_INLINE_LEN) {
-                /* do it inline */
-                memcpy(info->inline_symlink, symname, len);
-                inode->i_op = &shmem_symlink_inline_operations;
+        if (len <= SHORT_SYMLINK_LEN) {
+                info->symlink = kmemdup(symname, len, GFP_KERNEL);
+                if (!info->symlink) {
+                        iput(inode);
+                        return -ENOMEM;
+                }
+                inode->i_op = &shmem_short_symlink_operations;
         } else {
                 error = shmem_getpage(inode, 0, &page, SGP_WRITE, NULL);
                 if (error) {
@@ -1664,9 +1671,9 @@ static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *s
         return 0;
 }
 
-static void *shmem_follow_link_inline(struct dentry *dentry, struct nameidata *nd)
+static void *shmem_follow_short_symlink(struct dentry *dentry, struct nameidata *nd)
 {
-        nd_set_link(nd, SHMEM_I(dentry->d_inode)->inline_symlink);
+        nd_set_link(nd, SHMEM_I(dentry->d_inode)->symlink);
         return NULL;
 }
 
@@ -1914,9 +1921,9 @@ static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
 }
 #endif /* CONFIG_TMPFS_XATTR */
 
-static const struct inode_operations shmem_symlink_inline_operations = {
+static const struct inode_operations shmem_short_symlink_operations = {
         .readlink       = generic_readlink,
-        .follow_link    = shmem_follow_link_inline,
+        .follow_link    = shmem_follow_short_symlink,
 #ifdef CONFIG_TMPFS_XATTR
         .setxattr       = shmem_setxattr,
         .getxattr       = shmem_getxattr,
@@ -2259,10 +2266,8 @@ static void shmem_destroy_callback(struct rcu_head *head)
 
 static void shmem_destroy_inode(struct inode *inode)
 {
-        if ((inode->i_mode & S_IFMT) == S_IFREG) {
-                /* only struct inode is valid if it's an inline symlink */
+        if ((inode->i_mode & S_IFMT) == S_IFREG)
                 mpol_free_shared_policy(&SHMEM_I(inode)->policy);
-        }
         call_rcu(&inode->i_rcu, shmem_destroy_callback);
 }