[PATCH] Optimize select/poll by putting small data sets on the stack

[mv-sheeva.git] / fs / select.c

diff --git a/fs/select.c b/fs/select.c
index 1815a57d225585122c22dd0a357dbdced59e1c40..d8b4f0722b8d8cec0e58e048498ed9d366e28893 100644 (file)
--- a/fs/select.c
+++ b/fs/select.c
@@ -29,12 +29,6 @@
 #define ROUND_UP(x,y) (((x)+(y)-1)/(y))
 #define DEFAULT_POLLMASK (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)
 
-struct poll_table_entry {
-       struct file * filp;
-       wait_queue_t wait;
-       wait_queue_head_t * wait_address;
-};
-
 struct poll_table_page {
        struct poll_table_page * next;
        struct poll_table_entry * entry;
@@ -64,13 +58,23 @@ void poll_initwait(struct poll_wqueues *pwq)
        init_poll_funcptr(&pwq->pt, __pollwait);
        pwq->error = 0;
        pwq->table = NULL;
+       pwq->inline_index = 0;
 }
 
 EXPORT_SYMBOL(poll_initwait);
 
+static void free_poll_entry(struct poll_table_entry *entry)
+{
+       remove_wait_queue(entry->wait_address,&entry->wait);
+       fput(entry->filp);
+}
+
 void poll_freewait(struct poll_wqueues *pwq)
 {
        struct poll_table_page * p = pwq->table;
+       int i;
+       for (i = 0; i < pwq->inline_index; i++)
+               free_poll_entry(pwq->inline_entries + i);
        while (p) {
                struct poll_table_entry * entry;
                struct poll_table_page *old;
@@ -78,8 +82,7 @@ void poll_freewait(struct poll_wqueues *pwq)
                entry = p->entry;
                do {
                        entry--;
-                       remove_wait_queue(entry->wait_address,&entry->wait);
-                       fput(entry->filp);
+                       free_poll_entry(entry);
                } while (entry > p->entries);
                old = p;
                p = p->next;
@@ -89,12 +92,14 @@ void poll_freewait(struct poll_wqueues *pwq)
 
 EXPORT_SYMBOL(poll_freewait);
 
-static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
-                      poll_table *_p)
+static struct poll_table_entry *poll_get_entry(poll_table *_p)
 {
        struct poll_wqueues *p = container_of(_p, struct poll_wqueues, pt);
        struct poll_table_page *table = p->table;
 
+       if (p->inline_index < N_INLINE_POLL_ENTRIES)
+               return p->inline_entries + p->inline_index++;
+
        if (!table || POLL_TABLE_FULL(table)) {
                struct poll_table_page *new_table;
 
@@ -102,7 +107,7 @@ static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
                if (!new_table) {
                        p->error = -ENOMEM;
                        __set_current_state(TASK_RUNNING);
-                       return;
+                       return NULL;
                }
                new_table->entry = new_table->entries;
                new_table->next = table;
@@ -110,16 +115,21 @@ static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
                table = new_table;
        }
 
-       /* Add a new entry */
-       {
-               struct poll_table_entry * entry = table->entry;
-               table->entry = entry+1;
-               get_file(filp);
-               entry->filp = filp;
-               entry->wait_address = wait_address;
-               init_waitqueue_entry(&entry->wait, current);
-               add_wait_queue(wait_address,&entry->wait);
-       }
+       return table->entry++;
+}
+
+/* Add a new entry */
+static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
+                               poll_table *p)
+{
+       struct poll_table_entry *entry = poll_get_entry(p);
+       if (!entry)
+               return;
+       get_file(filp);
+       entry->filp = filp;
+       entry->wait_address = wait_address;
+       init_waitqueue_entry(&entry->wait, current);
+       add_wait_queue(wait_address,&entry->wait);
 }
 
 #define FDS_IN(fds, n)         (fds->in + n)
@@ -284,16 +294,6 @@ int do_select(int n, fd_set_bits *fds, s64 *timeout)
        return retval;
 }
 
-static void *select_bits_alloc(int size)
-{
-       return kmalloc(6 * size, GFP_KERNEL);
-}
-
-static void select_bits_free(void *bits, int size)
-{
-       kfree(bits);
-}
-
 /*
  * We can actually return ERESTARTSYS instead of EINTR, but I'd
  * like to be certain this leads to no problems. So I return
@@ -312,6 +312,8 @@ static int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
        char *bits;
        int ret, size, max_fdset;
        struct fdtable *fdt;
+       /* Allocate small arguments on the stack to save memory and be faster */
+       char stack_fds[SELECT_STACK_ALLOC];
 
        ret = -EINVAL;
        if (n < 0)
@@ -332,7 +334,10 @@ static int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
         */
        ret = -ENOMEM;
        size = FDS_BYTES(n);
-       bits = select_bits_alloc(size);
+       if (6*size < SELECT_STACK_ALLOC)
+               bits = stack_fds;
+       else
+               bits = kmalloc(6 * size, GFP_KERNEL);
        if (!bits)
                goto out_nofds;
        fds.in      = (unsigned long *)  bits;
@@ -367,7 +372,8 @@ static int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
                ret = -EFAULT;
 
 out:
-       select_bits_free(bits, size);
+       if (bits != stack_fds)
+               kfree(bits);
 out_nofds:
        return ret;
 }
@@ -619,6 +625,9 @@ static int do_poll(unsigned int nfds,  struct poll_list *list,
        return count;
 }
 
+#define N_STACK_PPS ((sizeof(stack_pps) - sizeof(struct poll_list))  / \
+                       sizeof(struct pollfd))
+
 int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)
 {
        struct poll_wqueues table;
@@ -628,6 +637,9 @@ int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)
        struct poll_list *walk;
        struct fdtable *fdt;
        int max_fdset;
+       /* Allocate small arguments on the stack to save memory and be faster */
+       char stack_pps[POLL_STACK_ALLOC];
+       struct poll_list *stack_pp = NULL;
 
        /* Do a sanity check on nfds ... */
        rcu_read_lock();
@@ -645,14 +657,23 @@ int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)
        err = -ENOMEM;
        while(i!=0) {
                struct poll_list *pp;
-               pp = kmalloc(sizeof(struct poll_list)+
-                               sizeof(struct pollfd)*
-                               (i>POLLFD_PER_PAGE?POLLFD_PER_PAGE:i),
-                                       GFP_KERNEL);
-               if(pp==NULL)
-                       goto out_fds;
+               int num, size;
+               if (stack_pp == NULL)
+                       num = N_STACK_PPS;
+               else
+                       num = POLLFD_PER_PAGE;
+               if (num > i)
+                       num = i;
+               size = sizeof(struct poll_list) + sizeof(struct pollfd)*num;
+               if (!stack_pp)
+                       stack_pp = pp = (struct poll_list *)stack_pps;
+               else {
+                       pp = kmalloc(size, GFP_KERNEL);
+                       if (!pp)
+                               goto out_fds;
+               }
                pp->next=NULL;
-               pp->len = (i>POLLFD_PER_PAGE?POLLFD_PER_PAGE:i);
+               pp->len = num;
                if (head == NULL)
                        head = pp;
                else
@@ -660,7 +681,7 @@ int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)
 
                walk = pp;
                if (copy_from_user(pp->entries, ufds + nfds-i, 
-                               sizeof(struct pollfd)*pp->len)) {
+                               sizeof(struct pollfd)*num)) {
                        err = -EFAULT;
                        goto out_fds;
                }
@@ -689,7 +710,8 @@ out_fds:
        walk = head;
        while(walk!=NULL) {
                struct poll_list *pp = walk->next;
-               kfree(walk);
+               if (walk != stack_pp)
+                       kfree(walk);
                walk = pp;
        }
        poll_freewait(&table);