pgtable.c

/*
 * This file contains common routines for dealing with free of page tables
 *
 *  Derived from arch/powerpc/mm/tlb_64.c:
 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 *
 *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
 *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
 *    Copyright (C) 1996 Paul Mackerras
 *
 *  Derived from "arch/i386/mm/init.c"
 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Dave Engebretsen <engebret@us.ibm.com>
 *      Rework for PPC64 port.
 *
 *  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.
 */

#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/tlb.h>

static DEFINE_PER_CPU(struct pte_freelist_batch *, pte_freelist_cur);
static unsigned long pte_freelist_forced_free;

struct pte_freelist_batch
{
	struct rcu_head	rcu;
	unsigned int	index;
	pgtable_free_t	tables[0];
};

#define PTE_FREELIST_SIZE \
	((PAGE_SIZE - sizeof(struct pte_freelist_batch)) \
	  / sizeof(pgtable_free_t))

static void pte_free_smp_sync(void *arg)
{
	/* Do nothing, just ensure we sync with all CPUs */
}

/* This is only called when we are critically out of memory
 * (and fail to get a page in pte_free_tlb).
 */
static void pgtable_free_now(pgtable_free_t pgf)
{
	pte_freelist_forced_free++;

	smp_call_function(pte_free_smp_sync, NULL, 1);

	pgtable_free(pgf);
}

static void pte_free_rcu_callback(struct rcu_head *head)
{
	struct pte_freelist_batch *batch =
		container_of(head, struct pte_freelist_batch, rcu);
	unsigned int i;

	for (i = 0; i < batch->index; i++)
		pgtable_free(batch->tables[i]);

	free_page((unsigned long)batch);
}

static void pte_free_submit(struct pte_freelist_batch *batch)
{
	INIT_RCU_HEAD(&batch->rcu);
	call_rcu(&batch->rcu, pte_free_rcu_callback);
}

void pgtable_free_tlb(struct mmu_gather *tlb, pgtable_free_t pgf)
{
	/* This is safe since tlb_gather_mmu has disabled preemption */
        cpumask_t local_cpumask = cpumask_of_cpu(smp_processor_id());
	struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);

	if (atomic_read(&tlb->mm->mm_users) < 2 ||
	    cpus_equal(tlb->mm->cpu_vm_mask, local_cpumask)) {
		pgtable_free(pgf);
		return;
	}

	if (*batchp == NULL) {
		*batchp = (struct pte_freelist_batch *)__get_free_page(GFP_ATOMIC);
		if (*batchp == NULL) {
			pgtable_free_now(pgf);
			return;
		}
		(*batchp)->index = 0;
	}
	(*batchp)->tables[(*batchp)->index++] = pgf;
	if ((*batchp)->index == PTE_FREELIST_SIZE) {
		pte_free_submit(*batchp);
		*batchp = NULL;
	}
}

void pte_free_finish(void)
{
	/* This is safe since tlb_gather_mmu has disabled preemption */
	struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);

	if (*batchp == NULL)
		return;
	pte_free_submit(*batchp);
	*batchp = NULL;
}