Re: [PATCH] mempool_resize and sanity checks

From: Balbir Singh (balbir_soni@yahoo.com)
Date: Fri Mar 15 2002 - 19:38:34 EST


For some reason, it seems that the diffs did not
make it. Resending them

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In mempool_resize(), I plan to replace the calls
to spin_unlock_irqrestore() -> pool_free -> spin_lock_
irqsave with the new sequence. The newer code
has fewer calls to spin_lock_irqsave and spin_unlock_
restore(). I think the new code should execute faster.

I have tested this code on a UP, if somebody could
test the patch on an SMP box and let me know if it
works, I would be thankful. I also have a sample test
case that uses mempool_resize().

I have also added the BUG_ON sanity checks in
mempool_create().

New Code

if (new_min_nr < pool->min_nr) {
        pool->min_nr = new_min_nr;
        /*
         * Free possible excess elements.
         */
        INIT_LIST_HEAD(&tmp_pool_to_free);
        while (pool->curr_nr > pool->min_nr) {
                tmp = pool->elements.next;
                if (tmp == &pool->elements)
                        BUG();
                list_del(tmp);
                list_add(tmp, &tmp_pool_to_free);
                pool->curr_nr--;
        }
        spin_unlock_irqrestore(&pool->lock, flags);

        list_for_each(tmp, &tmp_pool_to_free) {
                element = tmp;
                pool->free(element, pool->pool_data);
        }
        return;
}

Original Code

if (new_min_nr < pool->min_nr) {
        pool->min_nr = new_min_nr;
        /*
         * Free possible excess elements.
         */
        while (pool->curr_nr > pool->min_nr) {
                tmp = pool->elements.next;
                if (tmp == &pool->elements)
                        BUG();
                list_del(tmp);
                element = tmp;
                pool->curr_nr--;
                spin_unlock_irqrestore(&pool->lock,
flags);

                pool->free(element, pool->pool_data);

                spin_lock_irqsave(&pool->lock, flags);
        }
        spin_unlock_irqrestore(&pool->lock, flags);
        return;
}

Diffs are attached.

Balbir

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--- mempool.c Tue Mar 12 19:21:33 2002
+++ mempool.c.new Tue Mar 5 10:37:19 2002
@@ -34,6 +34,9 @@
         mempool_t *pool;
         int i;
 
+ BUG_ON(!alloc_fn);
+ BUG_ON(!free_fn);
+
         pool = kmalloc(sizeof(*pool), GFP_KERNEL);
         if (!pool)
                 return NULL;
@@ -97,6 +100,7 @@
         void *element;
         unsigned long flags;
         struct list_head *tmp;
+ struct list_head tmp_pool_to_free;
 
         if (new_min_nr <= 0)
                 BUG();
@@ -107,20 +111,21 @@
                 /*
                  * Free possible excess elements.
                  */
+ INIT_LIST_HEAD(&tmp_pool_to_free);
                 while (pool->curr_nr > pool->min_nr) {
                         tmp = pool->elements.next;
                         if (tmp == &pool->elements)
                                 BUG();
                         list_del(tmp);
- element = tmp;
+ list_add(tmp, &tmp_pool_to_free);
                         pool->curr_nr--;
- spin_unlock_irqrestore(&pool->lock, flags);
+ }
+ spin_unlock_irqrestore(&pool->lock, flags);
 
+ list_for_each(tmp, &tmp_pool_to_free) {
+ element = tmp;
                         pool->free(element, pool->pool_data);
-
- spin_lock_irqsave(&pool->lock, flags);
                 }
- spin_unlock_irqrestore(&pool->lock, flags);
                 return;
         }
         delta = new_min_nr - pool->min_nr;

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