[patch doh/9] mempool simplify alloc

Nick Piggin
2005-04-12T13:06:58Z

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Whoops, this one should be 3/9. 3/9 should be 4/9, and so on.

--
SUSE Labs, Novell Inc.
quilt

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Mempool is pretty clever. Looks too clever for its own good.
It shouldn't really know so much about MM internals.

- don't guess about what effective page reclaim might involve.

- don't randomly flush out all dirty data if some unlikely thing
happens (alloc returns NULL). page reclaim can (sort of :P) handle
it.

I think the main motivation is trying to avoid pool->lock at all
costs. However the first allocation is attempted with __GFP_WAIT
cleared, so it will be 'can_try_harder' if it hits the page allocator.
So if allocation still fails, then we can probably afford to hit the
pool->lock - and what's the alternative? Try page reclaim and hit
zone->lru_lock?

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>

Index: linux-2.6/mm/mempool.c
===================================================================
--- linux-2.6.orig/mm/mempool.c 2005-04-12 22:47:02.000000000 +1000
+++ linux-2.6/mm/mempool.c 2005-04-12 22:47:02.000000000 +1000
@@ -198,36 +198,22 @@ void * mempool_alloc(mempool_t *pool, un
void *element;
unsigned long flags;
DEFINE_WAIT(wait);
- int gfp_nowait;
+ int gfp_temp;

+ might_sleep_if(gfp_mask & __GFP_WAIT);
+
gfp_mask |= __GFP_MEMPOOL;
gfp_mask |= __GFP_NORETRY; /* don't loop in __alloc_pages */
gfp_mask |= __GFP_NOWARN; /* failures are OK */
- gfp_nowait = gfp_mask & ~(__GFP_WAIT | __GFP_IO);

- might_sleep_if(gfp_mask & __GFP_WAIT);
+ gfp_temp = gfp_mask & ~__GFP_WAIT;
+
repeat_alloc:
- element = pool->alloc(gfp_nowait, pool->pool_data);
+
+ element = pool->alloc(gfp_temp, pool->pool_data);
if (likely(element != NULL))
return element;

- /*
- * If the pool is less than 50% full and we can perform effective
- * page reclaim then try harder to allocate an element.
- */
- mb();
- if ((gfp_mask & __GFP_FS) && (gfp_mask != gfp_nowait) &&
- (pool->curr_nr <= pool->min_nr/2)) {
- element = pool->alloc(gfp_mask, pool->pool_data);
- if (likely(element != NULL))
- return element;
- }
-
- /*
- * Kick the VM at this point.
- */
- wakeup_bdflush(0);
-
spin_lock_irqsave(&pool->lock, flags);
if (likely(pool->curr_nr)) {
element = remove_element(pool);
@@ -240,6 +226,8 @@ repeat_alloc:
if (!(gfp_mask & __GFP_WAIT))
return NULL;

+ /* Now start performing page reclaim */
+ gfp_temp = gfp_mask;
prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
mb();
if (!pool->curr_nr)