tmpfs: use kmemdup for short symlinks
Hugh Dickins [Wed, 3 Aug 2011 23:21:26 +0000 (16:21 -0700)]
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>

include/linux/shmem_fs.h
mm/shmem.c

index 0c8e952..9291ac3 100644 (file)
@@ -8,20 +8,15 @@
 
 /* inode in-kernel data */
 
-#define SHMEM_NR_DIRECT 16
-
-#define SHMEM_SYMLINK_INLINE_LEN (SHMEM_NR_DIRECT * sizeof(swp_entry_t))
-
 struct shmem_inode_info {
        spinlock_t              lock;
        unsigned long           flags;
        unsigned long           alloced;        /* data pages alloced to file */
-       unsigned long           swapped;        /* subtotal assigned to swap */
-       struct shared_policy    policy;         /* NUMA memory alloc policy */
        union {
-               swp_entry_t     i_direct[SHMEM_NR_DIRECT]; /* first blocks */
-               char            inline_symlink[SHMEM_SYMLINK_INLINE_LEN];
+               unsigned long   swapped;        /* subtotal assigned to swap */
+               char            *symlink;       /* unswappable short symlink */
        };
+       struct shared_policy    policy;         /* NUMA memory alloc policy */
        struct list_head        swaplist;       /* chain of maybes on swap */
        struct list_head        xattr_list;     /* list of shmem_xattr */
        struct inode            vfs_inode;
index 0f094a2..3a5be0f 100644 (file)
@@ -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);
 }