[RFC][PATCH] kmalloc_percpu updated - 2.5.32

[RFC][PATCH] kmalloc_percpu updated - 2.5.32

[Dipankar Sarma]

Hi Andrew/Rusty/Christoph,

Here is the latest version of kmalloc_percpu() which is the
dynamic equivalent of Rusty's per-cpu areas. It is based
on an original piece of code by Rusty which was extended to
interlace small objects into per-CPU cache lines.

The interfaces are -

void *kmalloc_percpu(size_t size, int flags);
void kfree_percpu(const void *);
per_cpu_ptr(ptr, cpu)
this_cpu_ptr(ptr)

get_cpu_ptr(ptr) [New]
put_cpu_ptr(ptr) [New]

long *rx_stat1, *rx_stat2;

rx_stat1 = kmalloc_percpu(sizeof(*rx_stat1), GFP_KERNEL);
/* error checking and stuff */
rx_stat2 = kmalloc_percpu(sizeof(*rx_stat2), GFP_KERNEL);
/* error checking and stuff */

CPU #0          CPU #1

------------------------------------
rx_stat1        rx_stat1        ^
rx_stat2        rx_stat2        |
                                |
                            SMP_CACHE_BYTES
                                |
                                |
                                v
------------------------------------

Currently kmalloc_percpu() is being used in the statctr code.

Apart from the get/put_cpu_ptr() interfaces, I cleaned up some
legacy code to adheare to proper coding styles.

I would really appreciate your comments/suggestions.

Thanks
-- 
Dipankar Sarma  <dipankar@in.ibm.com> http://lse.sourceforge.net
Linux Technology Center, IBM Software Lab, Bangalore, India.

kmalloc_percpu-2.5.32-1.patch
-----------------------------

diff -urN linux-2.5.32-base/include/linux/slab.h linux-2.5.32-kmalloc_percpu/include/linux/slab.h
--- linux-2.5.32-base/include/linux/slab.h	Wed Aug 28 00:56:42 2002
+++ linux-2.5.32-kmalloc_percpu/include/linux/slab.h	Sat Aug 31 14:06:57 2002
@@ -13,6 +13,8 @@
 
 #include	<linux/gfp.h>
 #include	<linux/types.h>
+#include 	<linux/smp.h>
+#include 	<linux/spinlock.h>
 
 /* flags for kmem_cache_alloc() */
 #define	SLAB_NOFS		GFP_NOFS
@@ -64,6 +66,45 @@
 
 extern int FASTCALL(kmem_cache_reap(int));
 
+#ifdef CONFIG_SMP
+
+struct percpu_data {
+	void *ptrs[NR_CPUS];
+	void *blkp;
+};
+
+#define per_cpu_ptr(ptr, cpu)                   \
+({                                              \
+        struct percpu_data *__p = (struct percpu_data *)~(unsigned long)(ptr); \
+        (__typeof__(ptr))__p->ptrs[(cpu)];	\
+})
+#define this_cpu_ptr(ptr) per_cpu_ptr(ptr, smp_processor_id())
+extern void *kmalloc_percpu(size_t size, int flags);
+extern void kfree_percpu(const void *);
+extern int percpu_interlaced_alloc(struct percpu_data *, size_t, int);
+extern void percpu_interlaced_free(struct percpu_data *);
+extern void percpu_data_sys_init(void);
+
+#else
+
+#define per_cpu_ptr(ptr, cpu) (ptr)
+#define this_cpu_ptr(ptr) (ptr)
+static inline void *kmalloc_percpu(size_t size, int flags)
+{
+	return kmalloc(size, flags);
+}
+static inline void kfree_percpu(const void *ptr)
+{	
+	kfree(ptr);
+}
+static inline void percpu_data_sys_init(void) { }
+
+#endif
+
+#define get_cpu_ptr(ptr) ({ preempt_disable(); this_cpu_ptr(ptr); })
+#define put_cpu_ptr(ptr) preempt_enable()
+
+
 /* System wide caches */
 extern kmem_cache_t	*vm_area_cachep;
 extern kmem_cache_t	*mm_cachep;
diff -urN linux-2.5.32-base/init/main.c linux-2.5.32-kmalloc_percpu/init/main.c
--- linux-2.5.32-base/init/main.c	Wed Aug 28 00:56:36 2002
+++ linux-2.5.32-kmalloc_percpu/init/main.c	Sat Aug 31 13:00:09 2002
@@ -437,6 +437,7 @@
 #endif
 	mem_init();
 	kmem_cache_sizes_init();
+	percpu_data_sys_init();
 	pgtable_cache_init();
 	pte_chain_init();
 	mempages = num_physpages;
diff -urN linux-2.5.32-base/kernel/ksyms.c linux-2.5.32-kmalloc_percpu/kernel/ksyms.c
--- linux-2.5.32-base/kernel/ksyms.c	Wed Aug 28 00:56:32 2002
+++ linux-2.5.32-kmalloc_percpu/kernel/ksyms.c	Sat Aug 31 13:00:09 2002
@@ -107,6 +107,10 @@
 EXPORT_SYMBOL(kmem_cache_size);
 EXPORT_SYMBOL(kmalloc);
 EXPORT_SYMBOL(kfree);
+#ifdef CONFIG_SMP
+EXPORT_SYMBOL(kmalloc_percpu);
+EXPORT_SYMBOL(kfree_percpu);
+#endif
 EXPORT_SYMBOL(vfree);
 EXPORT_SYMBOL(__vmalloc);
 EXPORT_SYMBOL(vmalloc);
diff -urN linux-2.5.32-base/mm/Makefile linux-2.5.32-kmalloc_percpu/mm/Makefile
--- linux-2.5.32-base/mm/Makefile	Wed Aug 28 00:56:51 2002
+++ linux-2.5.32-kmalloc_percpu/mm/Makefile	Sat Aug 31 13:00:09 2002
@@ -10,7 +10,7 @@
 O_TARGET := mm.o
 
 export-objs := shmem.o filemap.o mempool.o page_alloc.o \
-		page-writeback.o
+		page-writeback.o percpu_data.o
 
 obj-y	 := memory.o mmap.o filemap.o mprotect.o mlock.o mremap.o \
 	    vmalloc.o slab.o bootmem.o swap.o vmscan.o page_io.o \
@@ -18,4 +18,5 @@
 	    shmem.o highmem.o mempool.o msync.o mincore.o readahead.o \
 	    pdflush.o page-writeback.o rmap.o
 
+obj-$(CONFIG_SMP) += percpu_data.o
 include $(TOPDIR)/Rules.make
diff -urN linux-2.5.32-base/mm/percpu_data.c linux-2.5.32-kmalloc_percpu/mm/percpu_data.c
--- linux-2.5.32-base/mm/percpu_data.c	Thu Jan  1 05:30:00 1970
+++ linux-2.5.32-kmalloc_percpu/mm/percpu_data.c	Sat Aug 31 13:11:16 2002
@@ -0,0 +1,374 @@
+/*
+ * Dynamic Per-CPU Data Allocator.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (c) IBM Corporation, 2002
+ *
+ * Author:              Dipankar Sarma <dipankar@in.ibm.com>
+ * 			Ravikiran G. Thirumalai <kiran@in.ibm.com>
+ *
+ */
+
+#include <linux/smp.h>
+#include <linux/spinlock.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/cache.h>
+
+struct percpu_data_blklist {
+	struct list_head        blks;
+	struct list_head        *firstnotfull;
+	spinlock_t              lock;
+	size_t			objsize;
+	size_t			blksize;
+	kmem_cache_t		*cachep;
+	char			*cachename;
+};
+
+struct percpu_data_blk {
+	struct list_head        linkage; 
+	void             	*blkaddr[NR_CPUS]; 
+	unsigned int            usecount; 
+	int			*freearr;  
+	int			freehead;
+	struct percpu_data_blklist *blklist;
+};
+
+static struct percpu_data_blklist data_blklist[] = {
+	{
+		.blks =	LIST_HEAD_INIT(data_blklist[0].blks),
+		.firstnotfull =	&data_blklist[0].blks,
+		.lock =	SPIN_LOCK_UNLOCKED,
+		.objsize = 4,
+		.blksize = ((4 + SMP_CACHE_BYTES - 1) & ~(SMP_CACHE_BYTES - 1)),
+		.cachep = NULL,
+		.cachename = "percpu_data_4"
+	},
+	{
+		.blks =	LIST_HEAD_INIT(data_blklist[1].blks),
+		.firstnotfull =	&data_blklist[1].blks,
+		.lock =	SPIN_LOCK_UNLOCKED,
+		.objsize = 8,
+		.blksize = ((8 + SMP_CACHE_BYTES - 1) & ~(SMP_CACHE_BYTES - 1)),
+		.cachep = NULL,
+		.cachename = "percpu_data_8"
+	},
+	{
+		.blks =	LIST_HEAD_INIT(data_blklist[2].blks),
+		.firstnotfull =	&data_blklist[2].blks,
+		.lock =	SPIN_LOCK_UNLOCKED,
+		.objsize = 16,
+		.blksize = ((16 + SMP_CACHE_BYTES - 1) &
+					~(SMP_CACHE_BYTES - 1)),
+		.cachep = NULL,
+		.cachename = "percpu_data_16"
+	},
+#if PAGE_SIZE != 4096
+	{
+		.blks =	LIST_HEAD_INIT(data_blklist[3].blks),
+		.firstnotfull =	&data_blklist[3].blks,
+		.lock =	SPIN_LOCK_UNLOCKED,
+		.objsize = 32,
+		.blksize = ((32 + SMP_CACHE_BYTES - 1) &
+					~(SMP_CACHE_BYTES - 1)),
+		.cachep = NULL,
+		.cachename = "percpu_data_32"
+	}
+#endif
+};
+
+static int data_blklist_count = 
+	sizeof(data_blklist)/sizeof(struct percpu_data_blklist);
+
+/*
+ * Allocate a block descriptor structure and initialize it.  
+ * Returns the address of the block descriptor or NULL on failure.
+ */
+static struct percpu_data_blk *percpu_data_blk_alloc(
+		struct percpu_data_blklist *blklist, int flags)
+{
+	struct percpu_data_blk *blkp;
+	int i;
+	int count;
+
+	if (!(blkp = kmalloc(sizeof(struct percpu_data_blk), flags)))
+		goto out1;
+	INIT_LIST_HEAD(&blkp->linkage);
+	blkp->usecount = 0;
+	count = blklist->blksize / blklist->objsize;	
+	blkp->freearr = kmalloc(count, flags); 
+	if (!blkp->freearr)
+		goto out;
+	blkp->freehead = 0;
+	for (i = 0; i < count; i++)
+		blkp->freearr[i] = i+1;
+	blkp->freearr[i-1] = -1;	/* Marks the end of the array */
+	blkp->blklist = blklist;
+	return blkp;
+out:
+	kfree(blkp);
+out1:
+	return NULL;
+}
+
+/*
+ * Frees the block descriptor structure
+ */
+static void percpu_data_blk_free(struct percpu_data_blk *blkp)
+{
+	kfree(blkp);
+}
+
+/*
+ * Add a block to the percpu data object memory pool.
+ * Returns 0 on failure and 1 on success
+ */
+static int percpu_data_mem_grow(struct percpu_data_blklist *blklist, int flags)
+{
+	struct percpu_data_blk *blkp;
+	unsigned long save_flags;
+	int i;
+
+	if (!(blkp = percpu_data_blk_alloc(blklist, flags)))
+		goto out;
+
+	for (i = 0; i < NR_CPUS; i++) {
+		if (!cpu_possible(i))
+			continue;
+		blkp->blkaddr[i] = kmem_cache_alloc(blklist->cachep, flags);
+		if (!(blkp->blkaddr[i])) 
+			goto out1;
+		memset(blkp->blkaddr[i], 0, blklist->blksize);
+	}
+
+	/* 
+	 * Now that we have the block successfully allocated 
+	 * and instantiated..  add it.....
+	 */
+	spin_lock_irqsave(&blklist->lock, save_flags);
+	list_add_tail(&blkp->linkage, &blklist->blks);
+	if (blklist->firstnotfull == &blklist->blks)
+		blklist->firstnotfull = &blkp->linkage;
+	spin_unlock_irqrestore(&blklist->lock, save_flags);
+	return 1;
+ 
+out1:
+	i--;
+	for (; i >= 0; i--) {
+		if (!cpu_possible(i))
+			continue;
+		kmem_cache_free(blklist->cachep, blkp->blkaddr[i]);
+	}
+	percpu_data_blk_free(blkp);
+out:
+        return 0;
+}
+
+/*
+ * Initialise the main percpu data control structure.
+ */
+static void percpu_data_blklist_init(struct percpu_data_blklist *blklist)
+{
+	blklist->cachep = kmem_cache_create(blklist->cachename,
+			blklist->blksize, 0, SLAB_HWCACHE_ALIGN, 
+			NULL, NULL);
+	if (!blklist->cachep)
+		BUG();
+}
+
+
+static struct percpu_data_blklist *percpu_data_get_blklist(size_t size,
+					int flags)
+{
+	int i;
+	for (i = 0; i < data_blklist_count; i++) {
+		if (size > data_blklist[i].objsize)
+			continue;
+		return &data_blklist[i];
+	}
+	return NULL;
+}
+
+	
+/*
+ * Initialize the percpu_data subsystem.
+ */
+void __init percpu_data_sys_init(void)
+{
+	int i;
+	for (i = 0; i < data_blklist_count; i++) {
+		percpu_data_blklist_init(&data_blklist[i]);
+	}
+}
+
+/*
+ * Allocs an object from the block.  Returns back the object index.
+ */
+static int __percpu_interlaced_alloc_one(struct percpu_data_blklist *blklist, 
+				struct percpu_data_blk *blkp)
+{
+	unsigned int objidx;
+
+	objidx = blkp->freehead;
+	blkp->freehead = blkp->freearr[objidx];
+	blkp->usecount++;
+	if (blkp->freehead < 0) {
+		blklist->firstnotfull = blkp->linkage.next;
+	}
+	return objidx;
+}
+
+/*
+ * Allocate a per cpu data object and return a pointer to it.
+ */
+static int __percpu_interlaced_alloc(struct percpu_data *percpu,
+		struct percpu_data_blklist *blklist, int flags)
+{
+	struct percpu_data_blk *blkp;
+	unsigned long save_flags;
+	struct list_head *l;
+	int objidx;
+	int i;
+
+tryagain:
+ 
+	spin_lock_irqsave(&blklist->lock, save_flags);
+	l = blklist->firstnotfull;
+	if (l == &blklist->blks)
+		goto unlock_and_get_mem;
+	blkp = list_entry(l, struct percpu_data_blk, linkage);
+
+	objidx = __percpu_interlaced_alloc_one(blklist, blkp);
+	spin_unlock_irqrestore(&blklist->lock, save_flags);
+	/* 
+	 * Since we hold the lock and firstnotfull is not the
+	 * head list, we should be getting an object alloc here. firstnotfull 
+	 * can be pointing to head of the list when all the blks are 
+	 * full or when there're no blocks left 
+	 */
+	for (i = 0; i < NR_CPUS; i++) {
+		if (!cpu_possible(i))
+			continue;
+		percpu->ptrs[i] = blkp->blkaddr[i] + objidx * blklist->objsize;
+	}
+	percpu->blkp = (void *)blkp;
+	return 1;
+ 
+unlock_and_get_mem:
+ 
+	spin_unlock_irqrestore(&blklist->lock, save_flags);
+	if (percpu_data_mem_grow(blklist, flags))
+		goto tryagain;
+
+	return 0;
+}
+
+/*
+ * Allocate a per-cpu data object and return a pointer to it.
+ * Returns NULL on failure. 
+ */
+int percpu_interlaced_alloc(struct percpu_data *pdata, size_t size, int flags)
+{
+	struct percpu_data_blklist *blklist;
+	
+	blklist = percpu_data_get_blklist(size, flags);
+	if (blklist == NULL)
+		return 0;
+	return __percpu_interlaced_alloc(pdata, blklist, flags);
+}
+
+/*
+ * Frees memory associated with a percpu data block
+ */
+static void percpu_data_blk_destroy(struct percpu_data_blklist *blklist, 
+			struct percpu_data_blk *blkp)
+{
+	int i;
+
+	for (i = 0; i < NR_CPUS; i++) {
+		if (!cpu_possible(i))
+			continue;
+		kmem_cache_free(blklist->cachep, blkp->blkaddr[i]);
+	}
+	percpu_data_blk_free(blkp);
+}
+
+/*
+ * Frees an object from a block and fixes the freelist accdly.
+ * Frees the slab cache memory if a block gets empty during free.
+ */
+static void __percpu_interlaced_free(struct percpu_data_blklist *blklist,
+		struct percpu_data *percpu)
+{
+	struct percpu_data_blk *blkp;
+	int objidx;
+	int objoffset;
+	struct list_head *t;
+	unsigned long save_flags;
+
+	spin_lock_irqsave(&blklist->lock, save_flags);
+	blkp = (struct percpu_data_blk *)percpu->blkp;
+	objoffset = percpu->ptrs[0] - blkp->blkaddr[0];
+	objidx = objoffset / blklist->objsize;
+	kfree(percpu);
+
+	blkp->freearr[objidx] = blkp->freehead;
+	blkp->freehead = objidx;
+	blkp->usecount--;
+	if (blkp->freearr[objidx] < 0)  {
+		/* 
+		 * block was previously full and is now just partially full ..
+		 * so make firstnotfull pt to this block and fix list accdly 
+		 */
+		t = blklist->firstnotfull;
+		blklist->firstnotfull = &blkp->linkage;
+		if (blkp->linkage.next == t) {
+			spin_unlock_irqrestore(&blklist->lock, save_flags);
+			return;
+		}
+		list_del(&blkp->linkage);
+		list_add_tail(&blkp->linkage, t);
+		
+		spin_unlock_irqrestore(&blklist->lock, save_flags);
+		return;
+	}
+
+	if (blkp->usecount == 0) {
+		t = blklist->firstnotfull->prev;
+
+		list_del(&blkp->linkage);
+		if (blklist->firstnotfull == &blkp->linkage)
+			blklist->firstnotfull = t->next;
+
+		spin_unlock_irqrestore(&blklist->lock, save_flags);
+		percpu_data_blk_destroy(blklist, blkp);
+		return;
+	}
+
+	spin_unlock_irqrestore(&blklist->lock, save_flags);
+	return;
+}
+
+/*
+ * Frees up a percpu data object
+ */ 
+void percpu_interlaced_free(struct percpu_data *percpu)
+{
+	struct percpu_data_blk *blkp = percpu->blkp;
+	__percpu_interlaced_free(blkp->blklist, percpu);
+}
diff -urN linux-2.5.32-base/mm/slab.c linux-2.5.32-kmalloc_percpu/mm/slab.c
--- linux-2.5.32-base/mm/slab.c	Wed Aug 28 00:57:08 2002
+++ linux-2.5.32-kmalloc_percpu/mm/slab.c	Sat Aug 31 13:00:09 2002
@@ -1604,6 +1604,58 @@
 	return NULL;
 }
 
+#ifdef CONFIG_SMP
+/**
+ * kmalloc_percpu - allocate one copy of the object for every present
+ * cpu in the system.
+ *
+ * @size: how many bytes of memory are required.
+ * @flags: the type of memory to allocate.
+ * The @flags argument may be one of:
+ *
+ * %GFP_USER - Allocate memory on behalf of user.  May sleep.
+ *
+ * %GFP_KERNEL - Allocate normal kernel ram.  May sleep.
+ *
+ * %GFP_ATOMIC - Allocation will not sleep.  Use inside interrupt handlers.
+ */
+void *kmalloc_percpu(size_t size, int flags)
+{
+        int i;
+        struct percpu_data *pdata = kmalloc(sizeof(*pdata), flags);
+ 
+        if (!pdata) 
+		goto out_done;
+	pdata->blkp = NULL;
+	if (size <= (cache_sizes[0].cs_size << 1)) {
+		if (!percpu_interlaced_alloc(pdata, size, flags))
+			goto out;
+	} else {
+		for (i = 0; i < NR_CPUS; i++) {
+			if (!cpu_possible(i))
+				continue;
+			pdata->ptrs[i] = kmalloc(size, flags);
+			if (!pdata->ptrs[i])
+				goto unwind_oom;
+		}
+	}
+        /* Catch derefs w/o wrappers */
+        return (void *)(~(unsigned long)pdata);
+ 
+unwind_oom:
+        while (--i >= 0) {
+		if (!cpu_possible(i))
+			continue;
+                kfree(pdata->ptrs[i]);
+	}
+out:
+        kfree(pdata);
+out_done:
+	return NULL;
+}
+#endif
+
+
 /**
  * kmem_cache_free - Deallocate an object
  * @cachep: The cache the allocation was from.
@@ -1656,6 +1708,32 @@
 	return cachep->objsize;
 }
 
+#ifdef CONFIG_SMP
+/**
+ * kfree_percpu - free previously allocated percpu memory
+ * @objp: pointer returned by kmalloc_percpu.
+ *
+ * Don't free memory not originally allocated by kmalloc_percpu()
+ * The complemented objp is to check for that.
+ */
+void kfree_percpu(const void *objp)
+{
+	int i;
+        struct percpu_data *p = (struct percpu_data *)(~(unsigned long)objp);
+
+	if (p->blkp) {
+		percpu_interlaced_free(p);
+	} else {
+		for (i = 0; i < NR_CPUS; i++) {
+			if (!cpu_possible(i))
+				continue;
+			kfree(p->ptrs[i]);
+		}
+	}
+}
+#endif
+
+
 kmem_cache_t * kmem_find_general_cachep (size_t size, int gfpflags)
 {
 	cache_sizes_t *csizep = cache_sizes;