[PATCH] fs: use kmalloc() to allocate fdmem if possible

[Changli Gao <xiaosuo@gmail.com>]

use kmalloc() to allocate fdmem if possible.

vmalloc() is used as a fallback solution for fdmem allocation. Two members are
added into the hole of the structure fdtable to indicate if vmalloc() is used
or not.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
----
 fs/file.c               |   33 ++++++++++++++++++++-------------
 include/linux/fdtable.h |    2 ++
 2 files changed, 22 insertions(+), 13 deletions(-)
diff --git a/fs/file.c b/fs/file.c
index 34bb7f7..f71dd85 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -39,28 +39,34 @@ int sysctl_nr_open_max = 1024 * 1024; /* raised later */
  */
 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
 
-static inline void * alloc_fdmem(unsigned int size)
+static inline void *alloc_fdmem(unsigned int size, unsigned short *use_vmalloc)
 {
-	if (size <= PAGE_SIZE)
-		return kmalloc(size, GFP_KERNEL);
-	else
-		return vmalloc(size);
+	void *data;
+
+	data = kmalloc(size, GFP_KERNEL);
+	if (data != NULL) {
+		*use_vmalloc = 0;
+		return data;
+	}
+	*use_vmalloc = 1;
+
+	return vmalloc(size);
 }
 
 static inline void free_fdarr(struct fdtable *fdt)
 {
-	if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
-		kfree(fdt->fd);
-	else
+	if (fdt->fdarr_vmalloc)
 		vfree(fdt->fd);
+	else
+		kfree(fdt->fd);
 }
 
 static inline void free_fdset(struct fdtable *fdt)
 {
-	if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
-		kfree(fdt->open_fds);
-	else
+	if (fdt->fdset_vmalloc)
 		vfree(fdt->open_fds);
+	else
+		kfree(fdt->open_fds);
 }
 
 static void free_fdtable_work(struct work_struct *work)
@@ -167,12 +173,13 @@ static struct fdtable * alloc_fdtable(unsigned int nr)
 	if (!fdt)
 		goto out;
 	fdt->max_fds = nr;
-	data = alloc_fdmem(nr * sizeof(struct file *));
+	data = alloc_fdmem(nr * sizeof(struct file *), &fdt->fdarr_vmalloc);
 	if (!data)
 		goto out_fdt;
 	fdt->fd = (struct file **)data;
 	data = alloc_fdmem(max_t(unsigned int,
-				 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
+				 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES),
+			   &fdt->fdset_vmalloc);
 	if (!data)
 		goto out_arr;
 	fdt->open_fds = (fd_set *)data;
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 013dc52..1e730bc 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -30,6 +30,8 @@ struct embedded_fd_set {
 
 struct fdtable {
 	unsigned int max_fds;
+	unsigned short fdarr_vmalloc;
+	unsigned short fdset_vmalloc;
 	struct file ** fd;      /* current fd array */
 	fd_set *close_on_exec;
 	fd_set *open_fds;