idr: idr_alloc() shouldn't trigger lowmem warning when preloaded

GFP_NOIO is often used for idr_alloc() inside preloaded section as the allocation mask doesn't really matter. If the idr tree needs to be expanded, idr_alloc() first tries to allocate using the specified allocation mask and if it fails falls back to the preloaded buffer. This order prevent non-preloading idr_alloc() users from taking advantage of preloading ones by using preload buffer without filling it shifting the burden of allocation to the preload users. Unfortunately, this allowed/expected-to-fail kmem_cache allocation ends up generating spurious slab lowmem warning before succeeding the request from the preload buffer. This patch makes idr_layer_alloc() add __GFP_NOWARN to the first kmem_cache attempt and try kmem_cache again w/o __GFP_NOWARN after allocation from preload_buffer fails so that lowmem warning is generated if not suppressed by the original @gfp_mask.

Tejun Heo committed 13 years ago

Commit 59bfbcf1 parent 415586c1 file · +25 −13Browse files

Unified · Split

lib/idr.c+25−13

@@ -106,8 +106,14 @@ static struct idr_layer idr_layer_alloc(gfp_t gfp_mask, struct idr layer_idr) · 105 unmodified lines
106	106	if (layer_idr)
107	107	return get_from_free_list(layer_idr);
108	108
109		− /* try to allocate directly from kmem_cache */
110		− new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
	109	+ /*
	110	+ * Try to allocate directly from kmem_cache. We want to try this
	111	+ * before preload buffer; otherwise, non-preloading idr_alloc()
	112	+ * users will end up taking advantage of preloading ones. As the
	113	+ * following is allowed to fail for preloaded cases, suppress
	114	+ * warning this time.
	115	+ */
	116	+ new = kmem_cache_zalloc(idr_layer_cache, gfp_mask \| __GFP_NOWARN);
111	117	if (new)
112	118	return new;
113	119
@@ -115,18 +121,24 @@ static struct idr_layer idr_layer_alloc(gfp_t gfp_mask, struct idr layer_idr) · 1 unmodified line
115	121	* Try to fetch one from the per-cpu preload buffer if in process
116	122	* context. See idr_preload() for details.
117	123	*/
118		− if (in_interrupt())
119		− return NULL;
120		−
121		− preempt_disable();
122		− new = __this_cpu_read(idr_preload_head);
123		− if (new) {
124		− __this_cpu_write(idr_preload_head, new->ary[0]);
125		− __this_cpu_dec(idr_preload_cnt);
126		− new->ary[0] = NULL;
	124	+ if (!in_interrupt()) {
	125	+ preempt_disable();
	126	+ new = __this_cpu_read(idr_preload_head);
	127	+ if (new) {
	128	+ __this_cpu_write(idr_preload_head, new->ary[0]);
	129	+ __this_cpu_dec(idr_preload_cnt);
	130	+ new->ary[0] = NULL;
	131	+ }
	132	+ preempt_enable();
	133	+ if (new)
	134	+ return new;
127	135	}
128		− preempt_enable();
129		− return new;
	136	+
	137	+ /*
	138	+ * Both failed. Try kmem_cache again w/o adding __GFP_NOWARN so
	139	+ * that memory allocation failure warning is printed as intended.
	140	+ */
	141	+ return kmem_cache_zalloc(idr_layer_cache, gfp_mask);
130	142	}
131	143
132	144	static void idr_layer_rcu_free(struct rcu_head *head)