linux-kernel - [PATCH] Fix kmalloc slab creation sequence

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Date:	Mon, 29 Jun 2015 09:28:08 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	David Rientjes <rientjes@...gle.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Gavin Guo <gavin.guo@...onical.com>,
	Theodore Ts'o <tytso@....edu>,
	Pekka Enberg <penberg@...nel.org>
Subject: [PATCH] Fix kmalloc slab creation sequence

This patch restores the slab creation sequence that was broken by commit
4066c33d0308f8 and also reverts the portions that introduced the
KMALLOC_LOOP_XXX macros. Those can never really work since the slab creation
is much more complex than just going from a minimum to a maximum number.

The latest upstream kernel boots cleanly on my machine with a 64 bit x86
configuration under KVM using either SLAB or SLUB.

Fixes: 4066c33d0308f8 ("support the slub_debug boot option")
Signed-off-by: Christoph Lameter <cl@...ux.com>

Index: linux/include/linux/slab.h
===================================================================
--- linux.orig/include/linux/slab.h	2015-06-29 09:16:41.686106310 -0500
+++ linux/include/linux/slab.h	2015-06-29 09:16:41.686106310 -0500
@@ -153,30 +153,8 @@ size_t ksize(const void *);
 #define ARCH_KMALLOC_MINALIGN ARCH_DMA_MINALIGN
 #define KMALLOC_MIN_SIZE ARCH_DMA_MINALIGN
 #define KMALLOC_SHIFT_LOW ilog2(ARCH_DMA_MINALIGN)
-/*
- * The KMALLOC_LOOP_LOW is the definition for the for loop index start number
- * to create the kmalloc_caches object in create_kmalloc_caches(). The first
- * and the second are 96 and 192. You can see that in the kmalloc_index(), if
- * the KMALLOC_MIN_SIZE <= 32, then return 1 (96). If KMALLOC_MIN_SIZE <= 64,
- * then return 2 (192). If the KMALLOC_MIN_SIZE is bigger than 64, we don't
- * need to initialize 96 and 192. Go directly to start the KMALLOC_SHIFT_LOW.
- */
-#if KMALLOC_MIN_SIZE <= 32
-#define KMALLOC_LOOP_LOW 1
-#elif KMALLOC_MIN_SIZE <= 64
-#define KMALLOC_LOOP_LOW 2
-#else
-#define KMALLOC_LOOP_LOW KMALLOC_SHIFT_LOW
-#endif
-
 #else
 #define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)
-/*
- * The KMALLOC_MIN_SIZE of slub/slab/slob is 2^3/2^5/2^3. So, even slab is used.
- * The KMALLOC_MIN_SIZE <= 32. The kmalloc-96 and kmalloc-192 should also be
- * initialized.
- */
-#define KMALLOC_LOOP_LOW 1
 #endif

 /*
Index: linux/mm/slab_common.c
===================================================================
--- linux.orig/mm/slab_common.c	2015-06-29 09:16:41.686106310 -0500
+++ linux/mm/slab_common.c	2015-06-29 09:18:55.481973057 -0500
@@ -855,6 +855,12 @@ void __init setup_kmalloc_cache_index_ta
 	}
 }

+static void new_kmalloc_cache(int idx, unsigned long flags)
+{
+	kmalloc_caches[idx] = create_kmalloc_cache(kmalloc_info[idx].name,
+					kmalloc_info[idx].size, flags);
+}
+
 /*
  * Create the kmalloc array. Some of the regular kmalloc arrays
  * may already have been created because they were needed to
@@ -864,25 +870,19 @@ void __init create_kmalloc_caches(unsign
 {
 	int i;

-	for (i = KMALLOC_LOOP_LOW; i <= KMALLOC_SHIFT_HIGH; i++) {
-		if (!kmalloc_caches[i]) {
-			kmalloc_caches[i] = create_kmalloc_cache(
-						kmalloc_info[i].name,
-						kmalloc_info[i].size,
-						flags);
-		}
+	for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++) {
+		if (!kmalloc_caches[i])
+			new_kmalloc_cache(i, flags);

 		/*
-		 * "i == 2" is the "kmalloc-192" case which is the last special
-		 * case for initialization and it's the point to jump to
-		 * allocate the minimize size of the object. In slab allocator,
-		 * the KMALLOC_SHIFT_LOW = 5. So, it needs to skip 2^3 and 2^4
-		 * and go straight to allocate 2^5. If the ARCH_DMA_MINALIGN is
-		 * defined, it may be larger than 2^5 and here is also the
-		 * trick to skip the empty gap.
+		 * Caches that are not of the two-to-the-power-of size.
+		 * These have to be created immediately after the
+		 * earlier power of two caches
 		 */
-		if (i == 2)
-			i = (KMALLOC_SHIFT_LOW - 1);
+		if (KMALLOC_MIN_SIZE <= 32 && !kmalloc_caches[1] && i == 6)
+			new_kmalloc_cache(1, flags);
+		if (KMALLOC_MIN_SIZE <= 64 && !kmalloc_caches[2] && i == 7)
+			new_kmalloc_cache(2, flags);
 	}

 	/* Kmalloc array is now usable */
--
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