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uClinux slab limits

RFC PATCH In review Christoph Hellwig 2 participants 2 messages Nov 14, 2002 Memory management

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Christoph Hellwig

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RFC PATCH 1/1 uClinux slab limits

Hi Manfred, Andrew,

I'm helping out Greg in getting the core uClinux bits merged and managed to get most stuff real non-intrusive. There's one thing I'd like to have a few comments on, that's the maximum allowed allocation size in the slab allocator. uClinux (aka the mmuless ports, the uClinux get a bit strange now that it's partially merged) don't support vmalloc naturally and thus need much large slab size, there's also an option to allow even large ones. Are the ifdefs in the below patch okay, or should we rather have an asm/ header for this?

mm/slab.c +38 -8
@@ -344,8 +344,20 @@
 
 #endif
 
-/* maximum size of an obj (in 2^order pages) */
+/*
+ * Maximum size of an obj (in 2^order pages)
+ * and absolute limit for the gfp order.
+ */
+#ifdef CONFIG_MMU
 #define	MAX_OBJ_ORDER	5	/* 32 pages */
+#define	MAX_GFP_ORDER	5	/* 32 pages */
+#elif defined (CONFIG_LARGE_ALLOCS)
+#define	MAX_OBJ_ORDER	13	/* up to 32Mb */
+#define	MAX_GFP_ORDER	13	/* up to 32Mb */
+#else
+#define	MAX_OBJ_ORDER	8	/* up to 1Mb */
+#define	MAX_GFP_ORDER	8	/* up to 1Mb */
+#endif
 
 /*
  * Do not go above this order unless 0 objects fit into the slab.

@@ -354,12 +366,6 @@
 #define	BREAK_GFP_ORDER_LO	1
 static int slab_break_gfp_order = BREAK_GFP_ORDER_LO;
 
-/*
- * Absolute limit for the gfp order
- */
-#define	MAX_GFP_ORDER	5	/* 32 pages */
-
-
 /* Macros for storing/retrieving the cachep and or slab from the
  * global 'mem_map'. These are used to find the slab an obj belongs to.
  * With kfree(), these are used to find the cache which an obj belongs to.

@@ -399,6 +405,18 @@
 	{ 32768,	NULL, NULL},
 	{ 65536,	NULL, NULL},
 	{131072,	NULL, NULL},
+#ifndef CONFIG_MMU
+	{262144,	NULL, NULL},
+	{524288,	NULL, NULL},
+	{1048576,	NULL, NULL},
+#ifdef CONFIG_LARGE_ALLOCS
+	{2097152,	NULL, NULL},
+	{4194304,	NULL, NULL},
+	{8388608,	NULL, NULL},
+	{16777216,	NULL, NULL},
+	{33554432,	NULL, NULL},
+#endif /* CONFIG_LARGE_ALLOCS */
+#endif /* CONFIG_MMU */
 	{     0,	NULL, NULL}
 };
 /* Must match cache_sizes above. Out of line to keep cache footprint low. */

@@ -427,7 +445,19 @@
 	CN("size-16384"),
 	CN("size-32768"),
 	CN("size-65536"),
-	CN("size-131072")
+	CN("size-131072"),
+#ifndef CONFIG_MMU
+	CN("size-262144"),
+	CN("size-524288"),
+	CN("size-1048576"),
+#ifdef CONFIG_LARGE_ALLOCS
+	CN("size-2097152"),
+	CN("size-4194304"),
+	CN("size-8388608"),
+	CN("size-16777216"),
+	CN("size-33554432"),
+#endif /* CONFIG_LARGE_ALLOCS */
+#endif /* CONFIG_MMU */
 }; 
 #undef CN

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#1 lore raw
Quoted 6 lines · Christoph Hellwig
mm/slab.c +4 -0
+#ifndef CONFIG_MMU
+       CN("size-262144"),
+       CN("size-524288"),
+       CN("size-1048576"),

mm/slab.c line 462

Quoted 10 lines
mm/slab.c +8 -0
+#ifdef CONFIG_LARGE_ALLOCS
+       CN("size-2097152"),
+       CN("size-4194304"),
+       CN("size-8388608"),
+       CN("size-16777216"),
+       CN("size-33554432"),
+#endif /* CONFIG_LARGE_ALLOCS */
+#endif /* CONFIG_MMU */
 };
 #undef CN

You could just do:

#if CONFIG_LARGEST_SLAB_ORDER >= 20
	CN("size-1048576"),
#endif
#if CONFIG_LARGEST_SLAB_ORDER >= 21
	CN("size-2097152"),
#endif
#if CONFIG_LARGEST_SLAB_ORDER >= 22
	CN("size-4194304"),

#endif

etcetera.

But I think it'd be better to just remove those statically initialised tables and put a good old for-loop in kmem_cache_init().
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