linux/fs/file.c
Eric Dumazet 0c9e63fd38 [PATCH] Shrinks sizeof(files_struct) and better layout
1) Reduce the size of (struct fdtable) to exactly 64 bytes on 32bits
   platforms, lowering kmalloc() allocated space by 50%.

2) Reduce the size of (files_struct), using a special 32 bits (or
   64bits) embedded_fd_set, instead of a 1024 bits fd_set for the
   close_on_exec_init and open_fds_init fields.  This save some ram (248
   bytes per task) as most tasks dont open more than 32 files.  D-Cache
   footprint for such tasks is also reduced to the minimum.

3) Reduce size of allocated fdset.  Currently two full pages are
   allocated, that is 32768 bits on x86 for example, and way too much.  The
   minimum is now L1_CACHE_BYTES.

UP and SMP should benefit from this patch, because most tasks will touch
only one cache line when open()/close() stdin/stdout/stderr (0/1/2),
(next_fd, close_on_exec_init, open_fds_init, fd_array[0 ..  2] being in the
same cache line)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-23 07:38:09 -08:00

378 lines
8.6 KiB
C

/*
* linux/fs/file.c
*
* Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
*
* Manage the dynamic fd arrays in the process files_struct.
*/
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/file.h>
#include <linux/bitops.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/workqueue.h>
struct fdtable_defer {
spinlock_t lock;
struct work_struct wq;
struct timer_list timer;
struct fdtable *next;
};
/*
* We use this list to defer free fdtables that have vmalloced
* sets/arrays. By keeping a per-cpu list, we avoid having to embed
* the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
* this per-task structure.
*/
static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
/*
* Allocate an fd array, using kmalloc or vmalloc.
* Note: the array isn't cleared at allocation time.
*/
struct file ** alloc_fd_array(int num)
{
struct file **new_fds;
int size = num * sizeof(struct file *);
if (size <= PAGE_SIZE)
new_fds = (struct file **) kmalloc(size, GFP_KERNEL);
else
new_fds = (struct file **) vmalloc(size);
return new_fds;
}
void free_fd_array(struct file **array, int num)
{
int size = num * sizeof(struct file *);
if (!array) {
printk (KERN_ERR "free_fd_array: array = 0 (num = %d)\n", num);
return;
}
if (num <= NR_OPEN_DEFAULT) /* Don't free the embedded fd array! */
return;
else if (size <= PAGE_SIZE)
kfree(array);
else
vfree(array);
}
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_fd_array(fdt->fd, fdt->max_fds);
kfree(fdt);
}
static void fdtable_timer(unsigned long data)
{
struct fdtable_defer *fddef = (struct fdtable_defer *)data;
spin_lock(&fddef->lock);
/*
* If someone already emptied the queue return.
*/
if (!fddef->next)
goto out;
if (!schedule_work(&fddef->wq))
mod_timer(&fddef->timer, 5);
out:
spin_unlock(&fddef->lock);
}
static void free_fdtable_work(struct fdtable_defer *f)
{
struct fdtable *fdt;
spin_lock_bh(&f->lock);
fdt = f->next;
f->next = NULL;
spin_unlock_bh(&f->lock);
while(fdt) {
struct fdtable *next = fdt->next;
__free_fdtable(fdt);
fdt = next;
}
}
static void free_fdtable_rcu(struct rcu_head *rcu)
{
struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
int fdset_size, fdarray_size;
struct fdtable_defer *fddef;
BUG_ON(!fdt);
fdset_size = fdt->max_fdset / 8;
fdarray_size = fdt->max_fds * sizeof(struct file *);
if (fdt->free_files) {
/*
* The this fdtable was embedded in the files structure
* and the files structure itself was getting destroyed.
* It is now safe to free the files structure.
*/
kmem_cache_free(files_cachep, fdt->free_files);
return;
}
if (fdt->max_fdset <= EMBEDDED_FD_SET_SIZE &&
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);
kfree(fdt->fd);
kfree(fdt);
} else {
fddef = &get_cpu_var(fdtable_defer_list);
spin_lock(&fddef->lock);
fdt->next = fddef->next;
fddef->next = fdt;
/*
* vmallocs are handled from the workqueue context.
* If the per-cpu workqueue is running, then we
* defer work scheduling through a timer.
*/
if (!schedule_work(&fddef->wq))
mod_timer(&fddef->timer, 5);
spin_unlock(&fddef->lock);
put_cpu_var(fdtable_defer_list);
}
}
void free_fdtable(struct fdtable *fdt)
{
if (fdt->free_files ||
fdt->max_fdset > EMBEDDED_FD_SET_SIZE ||
fdt->max_fds > NR_OPEN_DEFAULT)
call_rcu(&fdt->rcu, free_fdtable_rcu);
}
/*
* Expand the fdset in the files_struct. Called with the files spinlock
* held for write.
*/
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;
/*
* Don't copy the entire array if the current fdset is
* not yet initialised.
*/
if (i) {
memcpy (nfdt->open_fds, fdt->open_fds,
fdt->max_fdset/8);
memcpy (nfdt->close_on_exec, fdt->close_on_exec,
fdt->max_fdset/8);
memset (&nfdt->open_fds->fds_bits[i], 0, count);
memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
}
/* Don't copy/clear the array if we are creating a new
fd array for fork() */
if (fdt->max_fds) {
memcpy(nfdt->fd, fdt->fd,
fdt->max_fds * sizeof(struct file *));
/* clear the remainder of the array */
memset(&nfdt->fd[fdt->max_fds], 0,
(nfdt->max_fds - fdt->max_fds) *
sizeof(struct file *));
}
}
/*
* Allocate an fdset array, using kmalloc or vmalloc.
* Note: the array isn't cleared at allocation time.
*/
fd_set * alloc_fdset(int num)
{
fd_set *new_fdset;
int size = num / 8;
if (size <= PAGE_SIZE)
new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
else
new_fdset = (fd_set *) vmalloc(size);
return new_fdset;
}
void free_fdset(fd_set *array, int num)
{
if (num <= EMBEDDED_FD_SET_SIZE) /* Don't free an embedded fdset */
return;
else if (num <= 8 * PAGE_SIZE)
kfree(array);
else
vfree(array);
}
static struct fdtable *alloc_fdtable(int nr)
{
struct fdtable *fdt = NULL;
int nfds = 0;
fd_set *new_openset = NULL, *new_execset = NULL;
struct file **new_fds;
fdt = kzalloc(sizeof(*fdt), GFP_KERNEL);
if (!fdt)
goto out;
nfds = 8 * L1_CACHE_BYTES;
/* Expand to the max in easy steps */
while (nfds <= nr) {
nfds = nfds * 2;
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
* we have enough for the requested fd array size.
*/
do {
#if NR_OPEN_DEFAULT < 256
if (nfds < 256)
nfds = 256;
else
#endif
if (nfds < (PAGE_SIZE / sizeof(struct file *)))
nfds = PAGE_SIZE / sizeof(struct file *);
else {
nfds = nfds * 2;
if (nfds > NR_OPEN)
nfds = NR_OPEN;
}
} while (nfds <= nr);
new_fds = alloc_fd_array(nfds);
if (!new_fds)
goto out;
fdt->fd = new_fds;
fdt->max_fds = nfds;
fdt->free_files = NULL;
return fdt;
out:
if (new_openset)
free_fdset(new_openset, nfds);
if (new_execset)
free_fdset(new_execset, nfds);
kfree(fdt);
return NULL;
}
/*
* Expands the file descriptor table - it will allocate a new fdtable and
* both fd array and fdset. It is expected to be called with the
* files_lock held.
*/
static int expand_fdtable(struct files_struct *files, int nr)
__releases(files->file_lock)
__acquires(files->file_lock)
{
int error = 0;
struct fdtable *fdt;
struct fdtable *nfdt = NULL;
spin_unlock(&files->file_lock);
nfdt = alloc_fdtable(nr);
if (!nfdt) {
error = -ENOMEM;
spin_lock(&files->file_lock);
goto out;
}
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
/*
* Check again since another task may have expanded the
* fd table while we dropped the lock
*/
if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
copy_fdtable(nfdt, fdt);
} else {
/* Somebody expanded while we dropped file_lock */
spin_unlock(&files->file_lock);
__free_fdtable(nfdt);
spin_lock(&files->file_lock);
goto out;
}
rcu_assign_pointer(files->fdt, nfdt);
free_fdtable(fdt);
out:
return error;
}
/*
* Expand files.
* Return <0 on error; 0 nothing done; 1 files expanded, we may have blocked.
* Should be called with the files->file_lock spinlock held for write.
*/
int expand_files(struct files_struct *files, int nr)
{
int err, expand = 0;
struct fdtable *fdt;
fdt = files_fdtable(files);
if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
if (fdt->max_fdset >= NR_OPEN ||
fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
err = -EMFILE;
goto out;
}
expand = 1;
if ((err = expand_fdtable(files, nr)))
goto out;
}
err = expand;
out:
return err;
}
static void __devinit fdtable_defer_list_init(int cpu)
{
struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
spin_lock_init(&fddef->lock);
INIT_WORK(&fddef->wq, (void (*)(void *))free_fdtable_work, fddef);
init_timer(&fddef->timer);
fddef->timer.data = (unsigned long)fddef;
fddef->timer.function = fdtable_timer;
fddef->next = NULL;
}
void __init files_defer_init(void)
{
int i;
for_each_cpu(i)
fdtable_defer_list_init(i);
}