* Copyright 2001 Red Hat, Inc.
* Based on code from mm/memory.c Copyright Linus Torvalds and others.
*
+ * Copyright 2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
+ *
* 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
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
/*
- * For UP we don't need to worry about TLB flush
- * and page free order so much..
+ * Semi RCU freeing of the page directories.
+ *
+ * This is needed by some architectures to implement software pagetable walkers.
+ *
+ * gup_fast() and other software pagetable walkers do a lockless page-table
+ * walk and therefore needs some synchronization with the freeing of the page
+ * directories. The chosen means to accomplish that is by disabling IRQs over
+ * the walk.
+ *
+ * Architectures that use IPIs to flush TLBs will then automagically DTRT,
+ * since we unlink the page, flush TLBs, free the page. Since the disabling of
+ * IRQs delays the completion of the TLB flush we can never observe an already
+ * freed page.
+ *
+ * Architectures that do not have this (PPC) need to delay the freeing by some
+ * other means, this is that means.
+ *
+ * What we do is batch the freed directory pages (tables) and RCU free them.
+ * We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
+ * holds off grace periods.
+ *
+ * However, in order to batch these pages we need to allocate storage, this
+ * allocation is deep inside the MM code and can thus easily fail on memory
+ * pressure. To guarantee progress we fall back to single table freeing, see
+ * the implementation of tlb_remove_table_one().
+ *
*/
-#ifdef CONFIG_SMP
- #ifdef ARCH_FREE_PTR_NR
- #define FREE_PTR_NR ARCH_FREE_PTR_NR
- #else
- #define FREE_PTE_NR 506
- #endif
- #define tlb_fast_mode(tlb) ((tlb)->nr == ~0U)
-#else
- #define FREE_PTE_NR 1
- #define tlb_fast_mode(tlb) 1
+struct mmu_table_batch {
+ struct rcu_head rcu;
+ unsigned int nr;
+ void *tables[0];
+};
+
+#define MAX_TABLE_BATCH \
+ ((PAGE_SIZE - sizeof(struct mmu_table_batch)) / sizeof(void *))
+
+extern void tlb_table_flush(struct mmu_gather *tlb);
+extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
+
#endif
+/*
+ * If we can't allocate a page to make a big batch of page pointers
+ * to work on, then just handle a few from the on-stack structure.
+ */
+#define MMU_GATHER_BUNDLE 8
+
+struct mmu_gather_batch {
+ struct mmu_gather_batch *next;
+ unsigned int nr;
+ unsigned int max;
+ struct page *pages[0];
+};
+
+#define MAX_GATHER_BATCH \
+ ((PAGE_SIZE - sizeof(struct mmu_gather_batch)) / sizeof(void *))
+
/* struct mmu_gather is an opaque type used by the mm code for passing around
* any data needed by arch specific code for tlb_remove_page.
*/
struct mmu_gather {
struct mm_struct *mm;
- unsigned int nr; /* set to ~0U means fast mode */
- unsigned int need_flush;/* Really unmapped some ptes? */
- unsigned int fullmm; /* non-zero means full mm flush */
- struct page * pages[FREE_PTE_NR];
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+ struct mmu_table_batch *batch;
+#endif
+ unsigned int need_flush : 1, /* Did free PTEs */
+ fast_mode : 1; /* No batching */
+
+ unsigned int fullmm;
+
+ struct mmu_gather_batch *active;
+ struct mmu_gather_batch local;
+ struct page *__pages[MMU_GATHER_BUNDLE];
};
-/* Users of the generic TLB shootdown code must declare this storage space. */
-DECLARE_PER_CPU(struct mmu_gather, mmu_gathers);
+/*
+ * For UP we don't need to worry about TLB flush
+ * and page free order so much..
+ */
+#ifdef CONFIG_SMP
+ #define tlb_fast_mode(tlb) (tlb->fast_mode)
+#else
+ #define tlb_fast_mode(tlb) 1
+#endif
+
+static inline int tlb_next_batch(struct mmu_gather *tlb)
+{
+ struct mmu_gather_batch *batch;
+
+ batch = tlb->active;
+ if (batch->next) {
+ tlb->active = batch->next;
+ return 1;
+ }
+
+ batch = (void *)__get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
+ if (!batch)
+ return 0;
+
+ batch->next = NULL;
+ batch->nr = 0;
+ batch->max = MAX_GATHER_BATCH;
+
+ tlb->active->next = batch;
+ tlb->active = batch;
+
+ return 1;
+}
/* tlb_gather_mmu
- * Return a pointer to an initialized struct mmu_gather.
+ * Called to initialize an (on-stack) mmu_gather structure for page-table
+ * tear-down from @mm. The @fullmm argument is used when @mm is without
+ * users and we're going to destroy the full address space (exit/execve).
*/
-static inline struct mmu_gather *
-tlb_gather_mmu(struct mm_struct *mm, unsigned int full_mm_flush)
+static inline void
+tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm)
{
- struct mmu_gather *tlb = &get_cpu_var(mmu_gathers);
-
tlb->mm = mm;
- /* Use fast mode if only one CPU is online */
- tlb->nr = num_online_cpus() > 1 ? 0U : ~0U;
-
- tlb->fullmm = full_mm_flush;
+ tlb->fullmm = fullmm;
+ tlb->need_flush = 0;
+ tlb->fast_mode = (num_possible_cpus() == 1);
+ tlb->local.next = NULL;
+ tlb->local.nr = 0;
+ tlb->local.max = ARRAY_SIZE(tlb->__pages);
+ tlb->active = &tlb->local;
- return tlb;
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+ tlb->batch = NULL;
+#endif
}
static inline void
-tlb_flush_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
+tlb_flush_mmu(struct mmu_gather *tlb)
{
+ struct mmu_gather_batch *batch;
+
if (!tlb->need_flush)
return;
tlb->need_flush = 0;
tlb_flush(tlb);
- if (!tlb_fast_mode(tlb)) {
- free_pages_and_swap_cache(tlb->pages, tlb->nr);
- tlb->nr = 0;
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+ tlb_table_flush(tlb);
+#endif
+
+ if (tlb_fast_mode(tlb))
+ return;
+
+ for (batch = &tlb->local; batch; batch = batch->next) {
+ free_pages_and_swap_cache(batch->pages, batch->nr);
+ batch->nr = 0;
}
+ tlb->active = &tlb->local;
}
/* tlb_finish_mmu
static inline void
tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
{
- tlb_flush_mmu(tlb, start, end);
+ struct mmu_gather_batch *batch, *next;
+
+ tlb_flush_mmu(tlb);
/* keep the page table cache within bounds */
check_pgt_cache();
- put_cpu_var(mmu_gathers);
+ for (batch = tlb->local.next; batch; batch = next) {
+ next = batch->next;
+ free_pages((unsigned long)batch, 0);
+ }
+ tlb->local.next = NULL;
}
-/* tlb_remove_page
+/* __tlb_remove_page
* Must perform the equivalent to __free_pte(pte_get_and_clear(ptep)), while
* handling the additional races in SMP caused by other CPUs caching valid
- * mappings in their TLBs.
+ * mappings in their TLBs. Returns the number of free page slots left.
+ * When out of page slots we must call tlb_flush_mmu().
*/
-static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
+static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
{
+ struct mmu_gather_batch *batch;
+
tlb->need_flush = 1;
+
if (tlb_fast_mode(tlb)) {
free_page_and_swap_cache(page);
- return;
+ return 1; /* avoid calling tlb_flush_mmu() */
}
- tlb->pages[tlb->nr++] = page;
- if (tlb->nr >= FREE_PTE_NR)
- tlb_flush_mmu(tlb, 0, 0);
+
+ batch = tlb->active;
+ batch->pages[batch->nr++] = page;
+ VM_BUG_ON(batch->nr > batch->max);
+ if (batch->nr == batch->max) {
+ if (!tlb_next_batch(tlb))
+ return 0;
+ }
+
+ return batch->max - batch->nr;
+}
+
+/* tlb_remove_page
+ * Similar to __tlb_remove_page but will call tlb_flush_mmu() itself when
+ * required.
+ */
+static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
+{
+ if (!__tlb_remove_page(tlb, page))
+ tlb_flush_mmu(tlb);
}
/**
projects / mv-sheeva.git / blobdiff