idr: idr_alloc() shouldn't trigger lowmem warning when preloaded (59bfbcf0) · Commits · 戴 / test

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. Signed-off-by:

Tejun Heo <tj@kernel.org> Reported-by:

David Teigland <teigland@redhat.com> Tested-by:

David Teigland <teigland@redhat.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

lib/idr.c

+25 −13

Original line number	Diff line number	Diff line
		@@ -106,8 +106,14 @@ static struct idr_layer idr_layer_alloc(gfp_t gfp_mask, struct idr layer_idr)
		if (layer_idr)
		return get_from_free_list(layer_idr);

		/* try to allocate directly from kmem_cache */
		new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
		/*
		* Try to allocate directly from kmem_cache. We want to try this
		* before preload buffer; otherwise, non-preloading idr_alloc()
		* users will end up taking advantage of preloading ones. As the
		* following is allowed to fail for preloaded cases, suppress
		* warning this time.
		*/
		new = kmem_cache_zalloc(idr_layer_cache, gfp_mask \| __GFP_NOWARN);
		if (new)
		return new;

		@@ -115,9 +121,7 @@ static struct idr_layer idr_layer_alloc(gfp_t gfp_mask, struct idr layer_idr)
		* Try to fetch one from the per-cpu preload buffer if in process
		* context. See idr_preload() for details.
		*/
		if (in_interrupt())
		return NULL;

		if (!in_interrupt()) {
		preempt_disable();
		new = __this_cpu_read(idr_preload_head);
		if (new) {
		@@ -126,9 +130,17 @@ static struct idr_layer idr_layer_alloc(gfp_t gfp_mask, struct idr layer_idr)
		new->ary[0] = NULL;
		}
		preempt_enable();
		if (new)
		return new;
		}

		/*
		* Both failed. Try kmem_cache again w/o adding __GFP_NOWARN so
		* that memory allocation failure warning is printed as intended.
		*/
		return kmem_cache_zalloc(idr_layer_cache, gfp_mask);
		}

		static void idr_layer_rcu_free(struct rcu_head *head)
		{
		struct idr_layer *layer;

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