[PATCH] mempool: simplify alloc
Mempool is pretty clever. Looks too clever for its own good :) It
shouldn't really know so much about page reclaim 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?
A nice upshot is that we don't need to do any fancy memory barriers or do
(intentionally) racy access to pool-> fields outside the lock.
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/mempool.c b/mm/mempool.c
index d691b5c..e9a0a63 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -198,36 +198,22 @@
void *element;
unsigned long flags;
DEFINE_WAIT(wait);
- int gfp_nowait;
+ int gfp_temp;
+
+ might_sleep_if(gfp_mask & __GFP_WAIT);
gfp_mask |= __GFP_NOMEMALLOC; /* don't allocate emergency reserves */
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|__GFP_IO);
+
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 @@
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)