[PATCH] fdtable: Make fdarray and fdsets equal in size

Currently, each fdtable supports three dynamically-sized arrays of data: the
fdarray and two fdsets.  The code allows the number of fds supported by the
fdarray (fdtable->max_fds) to differ from the number of fds supported by each
of the fdsets (fdtable->max_fdset).

In practice, it is wasteful for these two sizes to differ: whenever we hit a
limit on the smaller-capacity structure, we will reallocate the entire fdtable
and all the dynamic arrays within it, so any delta in the memory used by the
larger-capacity structure will never be touched at all.

Rather than hogging this excess, we shouldn't even allocate it in the first
place, and keep the capacities of the fdarray and the fdsets equal.  This
patch removes fdtable->max_fdset.  As an added bonus, most of the supporting
code becomes simpler.
Signed-off-by: Vadim Lobanov <vlobanov@speakeasy.net>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/alpha/kernel/osf_sys.c

@@ -979,7 +979,7 @@ osf_select(int n, fd_set __user *inp, fd_set __user *outp, fd_set __user *exp,
 	long timeout;
 	int ret = -EINVAL;
 	struct fdtable *fdt;
-	int max_fdset;
+	int max_fds;
 
 	timeout = MAX_SCHEDULE_TIMEOUT;
 	if (tvp) {
@@ -1003,9 +1003,9 @@ osf_select(int n, fd_set __user *inp, fd_set __user *outp, fd_set __user *exp,
 
 	rcu_read_lock();
 	fdt = files_fdtable(current->files);
-	max_fdset = fdt->max_fdset;
+	max_fds = fdt->max_fds;
 	rcu_read_unlock();
-	if (n < 0 || n > max_fdset)
+	if (n < 0 || n > max_fds)
 		goto out_nofds;
 
 	/*

arch/mips/kernel/kspd.c

@@ -301,7 +301,7 @@ static void sp_cleanup(void)
 	for (;;) {
 		unsigned long set;
 		i = j * __NFDBITS;
-		if (i >= fdt->max_fdset || i >= fdt->max_fds)
+		if (i >= fdt->max_fds)
 			break;
 		set = fdt->open_fds->fds_bits[j++];
 		while (set) {

fs/compat.c

@@ -1679,19 +1679,19 @@ int compat_core_sys_select(int n, compat_ulong_t __user *inp,
 {
 	fd_set_bits fds;
 	char *bits;
-	int size, max_fdset, ret = -EINVAL;
+	int size, max_fds, ret = -EINVAL;
 	struct fdtable *fdt;
 
 	if (n < 0)
 		goto out_nofds;
 
-	/* max_fdset can increase, so grab it once to avoid race */
+	/* max_fds can increase, so grab it once to avoid race */
 	rcu_read_lock();
 	fdt = files_fdtable(current->files);
-	max_fdset = fdt->max_fdset;
+	max_fds = fdt->max_fds;
 	rcu_read_unlock();
-	if (n > max_fdset)
-		n = max_fdset;
+	if (n > max_fds)
+		n = max_fds;
 
 	/*
 	 * We need 6 bitmaps (in/out/ex for both incoming and outgoing),

fs/exec.c

@@ -783,7 +783,7 @@ static void flush_old_files(struct files_struct * files)
 		j++;
 		i = j * __NFDBITS;
 		fdt = files_fdtable(files);
-		if (i >= fdt->max_fds || i >= fdt->max_fdset)
+		if (i >= fdt->max_fds)
 			break;
 		set = fdt->close_on_exec->fds_bits[j];
 		if (!set)

fs/fcntl.c

@@ -77,10 +77,9 @@ repeat:
 		start = files->next_fd;
 
 	newfd = start;
-	if (start < fdt->max_fdset) {
+	if (start < fdt->max_fds)
 		newfd = find_next_zero_bit(fdt->open_fds->fds_bits,
-			fdt->max_fdset, start);
-	}
+					   fdt->max_fds, start);
 	
 	error = -EMFILE;
 	if (newfd >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)

fs/file.c

@@ -68,8 +68,8 @@ void free_fd_array(struct file **array, int num)
 
 static void __free_fdtable(struct fdtable *fdt)
 {
-	free_fdset(fdt->open_fds, fdt->max_fdset);
-	free_fdset(fdt->close_on_exec, fdt->max_fdset);
+	free_fdset(fdt->open_fds, fdt->max_fds);
+	free_fdset(fdt->close_on_exec, fdt->max_fds);
 	free_fd_array(fdt->fd, fdt->max_fds);
 	kfree(fdt);
 }
@@ -98,7 +98,7 @@ static void free_fdtable_rcu(struct rcu_head *rcu)
 	struct fdtable_defer *fddef;
 
 	BUG_ON(!fdt);
-	fdset_size = fdt->max_fdset / 8;
+	fdset_size = fdt->max_fds / 8;
 	fdarray_size = fdt->max_fds * sizeof(struct file *);
 
 	if (fdt->free_files) {
@@ -110,13 +110,11 @@ static void free_fdtable_rcu(struct rcu_head *rcu)
 		kmem_cache_free(files_cachep, fdt->free_files);
 		return;
 	}
-	if (fdt->max_fdset <= EMBEDDED_FD_SET_SIZE &&
-		fdt->max_fds <= NR_OPEN_DEFAULT) {
+	if (fdt->max_fds <= NR_OPEN_DEFAULT)
 		/*
 		 * The fdtable was embedded
 		 */
 		return;
-	}
 	if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
 		kfree(fdt->open_fds);
 		kfree(fdt->close_on_exec);
@@ -136,9 +134,7 @@ static void free_fdtable_rcu(struct rcu_head *rcu)
 
 void free_fdtable(struct fdtable *fdt)
 {
-	if (fdt->free_files ||
-		fdt->max_fdset > EMBEDDED_FD_SET_SIZE ||
-		fdt->max_fds > NR_OPEN_DEFAULT)
+	if (fdt->free_files || fdt->max_fds > NR_OPEN_DEFAULT)
 		call_rcu(&fdt->rcu, free_fdtable_rcu);
 }
 
@@ -151,12 +147,11 @@ static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
 	int i;
 	int count;
 
-	BUG_ON(nfdt->max_fdset < fdt->max_fdset);
 	BUG_ON(nfdt->max_fds < fdt->max_fds);
 	/* Copy the existing tables and install the new pointers */
 
-	i = fdt->max_fdset / (sizeof(unsigned long) * 8);
-	count = (nfdt->max_fdset - fdt->max_fdset) / 8;
+	i = fdt->max_fds / (sizeof(unsigned long) * 8);
+	count = (nfdt->max_fds - fdt->max_fds) / 8;
 
 	/*
 	 * Don't copy the entire array if the current fdset is
@@ -164,9 +159,9 @@ static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
 	 */
 	if (i) {
 		memcpy (nfdt->open_fds, fdt->open_fds,
-						fdt->max_fdset/8);
+						fdt->max_fds/8);
 		memcpy (nfdt->close_on_exec, fdt->close_on_exec,
-						fdt->max_fdset/8);
+						fdt->max_fds/8);
 		memset (&nfdt->open_fds->fds_bits[i], 0, count);
 		memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
 	}
@@ -201,7 +196,7 @@ fd_set * alloc_fdset(int num)
 
 void free_fdset(fd_set *array, int num)
 {
-	if (num <= EMBEDDED_FD_SET_SIZE) /* Don't free an embedded fdset */
+	if (num <= NR_OPEN_DEFAULT) /* Don't free an embedded fdset */
 		return;
 	else if (num <= 8 * PAGE_SIZE)
 		kfree(array);
@@ -220,18 +215,6 @@ static struct fdtable *alloc_fdtable(int nr)
 	if (!fdt)
   		goto out;
 
-	nfds = max_t(int, 8 * L1_CACHE_BYTES, roundup_pow_of_two(nr + 1));
-	if (nfds > NR_OPEN)
-		nfds = NR_OPEN;
-
-  	new_openset = alloc_fdset(nfds);
-  	new_execset = alloc_fdset(nfds);
-  	if (!new_openset || !new_execset)
-  		goto out;
-	fdt->open_fds = new_openset;
-	fdt->close_on_exec = new_execset;
-	fdt->max_fdset = nfds;
-
 	nfds = NR_OPEN_DEFAULT;
 	/*
 	 * Expand to the max in easy steps, and keep expanding it until
@@ -251,15 +234,21 @@ static struct fdtable *alloc_fdtable(int nr)
 				nfds = NR_OPEN;
   		}
 	} while (nfds <= nr);
+
+  	new_openset = alloc_fdset(nfds);
+  	new_execset = alloc_fdset(nfds);
+  	if (!new_openset || !new_execset)
+  		goto out;
+	fdt->open_fds = new_openset;
+	fdt->close_on_exec = new_execset;
+
 	new_fds = alloc_fd_array(nfds);
 	if (!new_fds)
-		goto out2;
+		goto out;
 	fdt->fd = new_fds;
 	fdt->max_fds = nfds;
 	fdt->free_files = NULL;
 	return fdt;
-out2:
-	nfds = fdt->max_fdset;
 out:
 	free_fdset(new_openset, nfds);
 	free_fdset(new_execset, nfds);
@@ -290,7 +279,7 @@ static int expand_fdtable(struct files_struct *files, int nr)
 	 * we dropped the lock
 	 */
 	cur_fdt = files_fdtable(files);
-	if (nr >= cur_fdt->max_fds || nr >= cur_fdt->max_fdset) {
+	if (nr >= cur_fdt->max_fds) {
 		/* Continue as planned */
 		copy_fdtable(new_fdt, cur_fdt);
 		rcu_assign_pointer(files->fdt, new_fdt);
@@ -316,11 +305,10 @@ int expand_files(struct files_struct *files, int nr)
 
 	fdt = files_fdtable(files);
 	/* Do we need to expand? */
-	if (nr < fdt->max_fdset && nr < fdt->max_fds)
+	if (nr < fdt->max_fds)
 		return 0;
 	/* Can we expand? */
-	if (fdt->max_fdset >= NR_OPEN || fdt->max_fds >= NR_OPEN ||
-	    nr >= NR_OPEN)
+	if (nr >= NR_OPEN)
 		return -EMFILE;
 
 	/* All good, so we try */

fs/open.c

@@ -864,8 +864,7 @@ int get_unused_fd(void)
 
 repeat:
 	fdt = files_fdtable(files);
- 	fd = find_next_zero_bit(fdt->open_fds->fds_bits,
-				fdt->max_fdset,
+	fd = find_next_zero_bit(fdt->open_fds->fds_bits, fdt->max_fds,
 				files->next_fd);
 
 	/*

fs/select.c

@@ -311,7 +311,7 @@ static int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
 {
 	fd_set_bits fds;
 	void *bits;
-	int ret, max_fdset;
+	int ret, max_fds;
 	unsigned int size;
 	struct fdtable *fdt;
 	/* Allocate small arguments on the stack to save memory and be faster */
@@ -321,13 +321,13 @@ static int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
 	if (n < 0)
 		goto out_nofds;
 
-	/* max_fdset can increase, so grab it once to avoid race */
+	/* max_fds can increase, so grab it once to avoid race */
 	rcu_read_lock();
 	fdt = files_fdtable(current->files);
-	max_fdset = fdt->max_fdset;
+	max_fds = fdt->max_fds;
 	rcu_read_unlock();
-	if (n > max_fdset)
-		n = max_fdset;
+	if (n > max_fds)
+		n = max_fds;
 
 	/*
 	 * We need 6 bitmaps (in/out/ex for both incoming and outgoing),

include/linux/file.h

@@ -26,14 +26,8 @@ struct embedded_fd_set {
 	unsigned long fds_bits[1];
 };
 
-/*
- * More than this number of fds: we use a separately allocated fd_set
- */
-#define EMBEDDED_FD_SET_SIZE (BITS_PER_BYTE * sizeof(struct embedded_fd_set))
-
 struct fdtable {
 	unsigned int max_fds;
-	int max_fdset;
 	struct file ** fd;      /* current fd array */
 	fd_set *close_on_exec;
 	fd_set *open_fds;

include/linux/init_task.h

@@ -12,7 +12,6 @@
 #define INIT_FDTABLE \
 {							\
 	.max_fds	= NR_OPEN_DEFAULT, 		\
-	.max_fdset	= EMBEDDED_FD_SET_SIZE,		\
 	.fd		= &init_files.fd_array[0], 	\
 	.close_on_exec	= (fd_set *)&init_files.close_on_exec_init, \
 	.open_fds	= (fd_set *)&init_files.open_fds_init, 	\

kernel/exit.c

@@ -425,7 +425,7 @@ static void close_files(struct files_struct * files)
 	for (;;) {
 		unsigned long set;
 		i = j * __NFDBITS;
-		if (i >= fdt->max_fdset || i >= fdt->max_fds)
+		if (i >= fdt->max_fds)
 			break;
 		set = fdt->open_fds->fds_bits[j++];
 		while (set) {

kernel/fork.c

@@ -614,7 +614,7 @@ static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
 
 static int count_open_files(struct fdtable *fdt)
 {
-	int size = fdt->max_fdset;
+	int size = fdt->max_fds;
 	int i;
 
 	/* Find the last open fd */
@@ -641,7 +641,6 @@ static struct files_struct *alloc_files(void)
 	newf->next_fd = 0;
 	fdt = &newf->fdtab;
 	fdt->max_fds = NR_OPEN_DEFAULT;
-	fdt->max_fdset = EMBEDDED_FD_SET_SIZE;
 	fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
 	fdt->open_fds = (fd_set *)&newf->open_fds_init;
 	fdt->fd = &newf->fd_array[0];
@@ -662,7 +661,7 @@ static struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 {
 	struct files_struct *newf;
 	struct file **old_fds, **new_fds;
-	int open_files, size, i, expand;
+	int open_files, size, i;
 	struct fdtable *old_fdt, *new_fdt;
 
 	*errorp = -ENOMEM;
@@ -673,25 +672,14 @@ static struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 	spin_lock(&oldf->file_lock);
 	old_fdt = files_fdtable(oldf);
 	new_fdt = files_fdtable(newf);
-	size = old_fdt->max_fdset;
 	open_files = count_open_files(old_fdt);
-	expand = 0;
 
 	/*
-	 * Check whether we need to allocate a larger fd array or fd set.
-	 * Note: we're not a clone task, so the open count won't  change.
+	 * Check whether we need to allocate a larger fd array and fd set.
+	 * Note: we're not a clone task, so the open count won't change.
 	 */
-	if (open_files > new_fdt->max_fdset) {
-		new_fdt->max_fdset = 0;
-		expand = 1;
-	}
 	if (open_files > new_fdt->max_fds) {
 		new_fdt->max_fds = 0;
-		expand = 1;
-	}
-
-	/* if the old fdset gets grown now, we'll only copy up to "size" fds */
-	if (expand) {
 		spin_unlock(&oldf->file_lock);
 		spin_lock(&newf->file_lock);
 		*errorp = expand_files(newf, open_files-1);
@@ -739,8 +727,8 @@ static struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 	/* This is long word aligned thus could use a optimized version */ 
 	memset(new_fds, 0, size); 
 
-	if (new_fdt->max_fdset > open_files) {
-		int left = (new_fdt->max_fdset-open_files)/8;
+	if (new_fdt->max_fds > open_files) {
+		int left = (new_fdt->max_fds-open_files)/8;
 		int start = open_files / (8 * sizeof(unsigned long));
 
 		memset(&new_fdt->open_fds->fds_bits[start], 0, left);

security/selinux/hooks.c

@@ -1734,7 +1734,7 @@ static inline void flush_unauthorized_files(struct files_struct * files)
 		j++;
 		i = j * __NFDBITS;
 		fdt = files_fdtable(files);
-		if (i >= fdt->max_fds || i >= fdt->max_fdset)
+		if (i >= fdt->max_fds)
 			break;
 		set = fdt->open_fds->fds_bits[j];
 		if (!set)