[PATCH] mempool: NOMEMALLOC and NORETRY

Mempools have 2 problems.

The first is that mempool_alloc can possibly get stuck in __alloc_pages
when they should opt to fail, and take an element from their reserved pool.

The second is that it will happily eat emergency PF_MEMALLOC reserves
instead of going to their reserved pools.

Fix the first by passing __GFP_NORETRY in the allocation calls in
mempool_alloc. Fix the second by introducing a __GFP_MEMPOOL flag which
directs the page allocator not to allocate from the reserve pool.

Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/gfp.h

···
 #define __GFP_NO_GROW	0x2000u	/* Slab internal usage */
 #define __GFP_COMP	0x4000u	/* Add compound page metadata */
 #define __GFP_ZERO	0x8000u	/* Return zeroed page on success */
+#define __GFP_NOMEMALLOC 0x10000u /* Don't use emergency reserves */
 
-#define __GFP_BITS_SHIFT 16	/* Room for 16 __GFP_FOO bits */
+#define __GFP_BITS_SHIFT 20	/* Room for 20 __GFP_FOO bits */
 #define __GFP_BITS_MASK ((1 << __GFP_BITS_SHIFT) - 1)
 
 /* if you forget to add the bitmask here kernel will crash, period */
 #define GFP_LEVEL_MASK (__GFP_WAIT|__GFP_HIGH|__GFP_IO|__GFP_FS| \
 			__GFP_COLD|__GFP_NOWARN|__GFP_REPEAT| \
-			__GFP_NOFAIL|__GFP_NORETRY|__GFP_NO_GROW|__GFP_COMP)
+			__GFP_NOFAIL|__GFP_NORETRY|__GFP_NO_GROW|__GFP_COMP| \
+			__GFP_NOMEMALLOC)
 
 #define GFP_ATOMIC	(__GFP_HIGH)
 #define GFP_NOIO	(__GFP_WAIT)

mm/mempool.c

···
 	void *element;
 	unsigned long flags;
 	DEFINE_WAIT(wait);
-	int gfp_nowait = gfp_mask & ~(__GFP_WAIT | __GFP_IO);
+	int gfp_nowait;
+
+	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);
 repeat_alloc:
-	element = pool->alloc(gfp_nowait|__GFP_NOWARN, pool->pool_data);
+	element = pool->alloc(gfp_nowait, pool->pool_data);
 	if (likely(element != NULL))
 		return element;
 

mm/page_alloc.c

···
 	}
 
 	/* This allocation should allow future memory freeing. */
-	if (((p->flags & PF_MEMALLOC) || unlikely(test_thread_flag(TIF_MEMDIE))) && !in_interrupt()) {
-		/* go through the zonelist yet again, ignoring mins */
-		for (i = 0; (z = zones[i]) != NULL; i++) {
-			if (!cpuset_zone_allowed(z))
-				continue;
-			page = buffered_rmqueue(z, order, gfp_mask);
-			if (page)
-				goto got_pg;
+
+	if (((p->flags & PF_MEMALLOC) || unlikely(test_thread_flag(TIF_MEMDIE)))
+			&& !in_interrupt()) {
+		if (!(gfp_mask & __GFP_NOMEMALLOC)) {
+			/* go through the zonelist yet again, ignoring mins */
+			for (i = 0; (z = zones[i]) != NULL; i++) {
+				if (!cpuset_zone_allowed(z))
+					continue;
+				page = buffered_rmqueue(z, order, gfp_mask);
+				if (page)
+					goto got_pg;
+			}
 		}
 		goto nopage;
 	}