From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Andrea Arcangeli <aarcange@redhat.com>,
Avi Kivity <avi@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
Rik van Riel <riel@redhat.com>, Ingo Molnar <mingo@elte.hu>,
akpm@linux-foundation.org,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
David Miller <davem@davemloft.net>,
Hugh Dickins <hugh.dickins@tiscali.co.uk>,
Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@suse.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: [PATCH 09/13] mm, powerpc: Move the RCU page-table freeing into generic code
Date: Thu, 08 Apr 2010 21:17:46 +0200 [thread overview]
Message-ID: <20100408192722.987227219@chello.nl> (raw)
In-Reply-To: 20100408191737.296180458@chello.nl
[-- Attachment #1: mm-preempt-tlb-gather-rcu.patch --]
[-- Type: text/plain, Size: 12888 bytes --]
In case other architectures require RCU freed page-tables to implement
gup_fast(), provide the means to do so by moving the logic into generic
code.
Requested-by: David Miller <davem@davemloft.net>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
arch/powerpc/include/asm/pgalloc.h | 23 ++++++-
arch/powerpc/include/asm/tlb.h | 10 ---
arch/powerpc/mm/pgtable.c | 119 -------------------------------------
arch/powerpc/mm/tlb_hash32.c | 3
arch/powerpc/mm/tlb_hash64.c | 3
arch/powerpc/mm/tlb_nohash.c | 3
include/asm-generic/tlb.h | 57 ++++++++++++++++-
mm/memory.c | 81 +++++++++++++++++++++++++
8 files changed, 153 insertions(+), 146 deletions(-)
Index: linux-2.6/arch/powerpc/include/asm/pgalloc.h
===================================================================
--- linux-2.6.orig/arch/powerpc/include/asm/pgalloc.h
+++ linux-2.6/arch/powerpc/include/asm/pgalloc.h
@@ -31,14 +31,31 @@ static inline void pte_free(struct mm_st
#endif
#ifdef CONFIG_SMP
-extern void pgtable_free_tlb(struct mmu_gather *tlb, void *table, unsigned shift);
-extern void pte_free_finish(struct mmu_gather *tlb);
+#define HAVE_ARCH_RCU_TABLE_FREE
+
+struct mmu_gather;
+extern void tlb_remove_table(struct mmu_gather *, void *);
+
+static inline void pgtable_free_tlb(struct mmu_gather *tlb, void *table, int shift)
+{
+ unsigned long pgf = (unsigned long)table;
+ BUG_ON(shift > MAX_PGTABLE_INDEX_SIZE);
+ pgf |= shift;
+ tlb_remove_table(tlb, (void *)pgf);
+}
+
+static inline void __tlb_remove_table(void *_table)
+{
+ void *table = (void *)((unsigned long)_table & ~MAX_PGTABLE_INDEX_SIZE);
+ unsigned shift = (unsigned long)_table & MAX_PGTABLE_INDEX_SIZE;
+
+ pgtable_free(table, shift);
+}
#else /* CONFIG_SMP */
static inline void pgtable_free_tlb(struct mmu_gather *tlb, void *table, unsigned shift)
{
pgtable_free(table, shift);
}
-static inline void pte_free_finish(struct mmu_gather *tlb) { }
#endif /* !CONFIG_SMP */
static inline void __pte_free_tlb(struct mmu_gather *tlb, struct page *ptepage,
Index: linux-2.6/arch/powerpc/include/asm/tlb.h
===================================================================
--- linux-2.6.orig/arch/powerpc/include/asm/tlb.h
+++ linux-2.6/arch/powerpc/include/asm/tlb.h
@@ -28,16 +28,6 @@
#define tlb_start_vma(tlb, vma) do { } while (0)
#define tlb_end_vma(tlb, vma) do { } while (0)
-#define HAVE_ARCH_MMU_GATHER 1
-
-struct pte_freelist_batch;
-
-struct arch_mmu_gather {
- struct pte_freelist_batch *batch;
-};
-
-#define ARCH_MMU_GATHER_INIT (struct arch_mmu_gather){ .batch = NULL, }
-
extern void tlb_flush(struct mmu_gather *tlb);
/* Get the generic bits... */
Index: linux-2.6/arch/powerpc/mm/pgtable.c
===================================================================
--- linux-2.6.orig/arch/powerpc/mm/pgtable.c
+++ linux-2.6/arch/powerpc/mm/pgtable.c
@@ -33,125 +33,6 @@
#include "mmu_decl.h"
-#ifdef CONFIG_SMP
-
-/*
- * Handle batching of page table freeing on SMP. Page tables are
- * queued up and send to be freed later by RCU in order to avoid
- * freeing a page table page that is being walked without locks
- */
-
-static unsigned long pte_freelist_forced_free;
-
-struct pte_freelist_batch
-{
- struct rcu_head rcu;
- unsigned int index;
- unsigned long tables[0];
-};
-
-#define PTE_FREELIST_SIZE \
- ((PAGE_SIZE - sizeof(struct pte_freelist_batch)) \
- / sizeof(unsigned long))
-
-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(void *table, unsigned shift)
-{
- pte_freelist_forced_free++;
-
- smp_call_function(pte_free_smp_sync, NULL, 1);
-
- pgtable_free(table, shift);
-}
-
-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++) {
- void *table = (void *)(batch->tables[i] & ~MAX_PGTABLE_INDEX_SIZE);
- unsigned shift = batch->tables[i] & MAX_PGTABLE_INDEX_SIZE;
-
- pgtable_free(table, shift);
- }
-
- 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, void *table, unsigned shift)
-{
- struct pte_freelist_batch **batchp = &tlb->arch.batch;
- unsigned long pgf;
-
- /*
- * A comment here about on why we have RCU freed page tables might be
- * interesting, also explaining why we don't need any sort of grace
- * period for mm_users == 1, and have some home brewn smp_call_func()
- * for single frees.
- *
- * The only lockless page table walker I know of is gup_fast() which
- * relies on irq_disable(). So my guess is that mm_users == 1 means
- * that there cannot be another thread and so precludes gup_fast()
- * concurrency.
- *
- * If there are, but we fail to batch, we need to IPI (all?) CPUs so as
- * to serialize against the IRQ disable. In case we do batch, the RCU
- * grace period is at least long enough to cover IRQ disabled sections
- * (XXX assumption, not strictly true).
- *
- * All this results in us doing our own free batching and not using
- * the generic mmu_gather batches (XXX fix that somehow?).
- */
-
- if (atomic_read(&tlb->mm->mm_users) < 2) {
- pgtable_free(table, shift);
- return;
- }
-
- if (*batchp == NULL) {
- *batchp = (struct pte_freelist_batch *)__get_free_page(GFP_ATOMIC);
- if (*batchp == NULL) {
- pgtable_free_now(table, shift);
- return;
- }
- (*batchp)->index = 0;
- }
- BUG_ON(shift > MAX_PGTABLE_INDEX_SIZE);
- pgf = (unsigned long)table | shift;
- (*batchp)->tables[(*batchp)->index++] = pgf;
- if ((*batchp)->index == PTE_FREELIST_SIZE) {
- pte_free_submit(*batchp);
- *batchp = NULL;
- }
-}
-
-void pte_free_finish(struct mmu_gather *tlb)
-{
- struct pte_freelist_batch **batchp = &tlb->arch.batch;
-
- if (*batchp == NULL)
- return;
- pte_free_submit(*batchp);
- *batchp = NULL;
-}
-
-#endif /* CONFIG_SMP */
-
static inline int is_exec_fault(void)
{
return current->thread.regs && TRAP(current->thread.regs) == 0x400;
Index: linux-2.6/arch/powerpc/mm/tlb_hash32.c
===================================================================
--- linux-2.6.orig/arch/powerpc/mm/tlb_hash32.c
+++ linux-2.6/arch/powerpc/mm/tlb_hash32.c
@@ -71,9 +71,6 @@ void tlb_flush(struct mmu_gather *tlb)
*/
_tlbia();
}
-
- /* Push out batch of freed page tables */
- pte_free_finish(tlb);
}
/*
Index: linux-2.6/arch/powerpc/mm/tlb_hash64.c
===================================================================
--- linux-2.6.orig/arch/powerpc/mm/tlb_hash64.c
+++ linux-2.6/arch/powerpc/mm/tlb_hash64.c
@@ -165,9 +165,6 @@ void tlb_flush(struct mmu_gather *tlb)
__flush_tlb_pending(tlbbatch);
put_cpu_var(ppc64_tlb_batch);
-
- /* Push out batch of freed page tables */
- pte_free_finish(tlb);
}
/**
Index: linux-2.6/arch/powerpc/mm/tlb_nohash.c
===================================================================
--- linux-2.6.orig/arch/powerpc/mm/tlb_nohash.c
+++ linux-2.6/arch/powerpc/mm/tlb_nohash.c
@@ -296,9 +296,6 @@ EXPORT_SYMBOL(flush_tlb_range);
void tlb_flush(struct mmu_gather *tlb)
{
flush_tlb_mm(tlb->mm);
-
- /* Push out batch of freed page tables */
- pte_free_finish(tlb);
}
/*
Index: linux-2.6/include/asm-generic/tlb.h
===================================================================
--- linux-2.6.orig/include/asm-generic/tlb.h
+++ linux-2.6/include/asm-generic/tlb.h
@@ -27,6 +27,49 @@
#define tlb_fast_mode(tlb) 1
#endif
+#ifdef HAVE_ARCH_RCU_TABLE_FREE
+/*
+ * Semi RCU freeing of the page directories.
+ *
+ * This is needed by some architectures to implement gup_fast().
+ *
+ * gup_fast() does 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 copmletion 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.
+ * The assumption that IRQ disabled also holds off RCU grace periods is valid
+ * for the current RCU implementations (if this ever were to change these
+ * gup_fast() implementation would need to use the RCU read lock).
+ *
+ * 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().
+ *
+ */
+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(unsigned long))
+
+extern void tlb_table_flush(struct mmu_gather *tlb);
+extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
+
+#endif
+
/* 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.
*/
@@ -36,11 +79,12 @@ struct mmu_gather {
unsigned int max; /* nr < max */
unsigned int need_flush;/* Really unmapped some ptes? */
unsigned int fullmm; /* non-zero means full mm flush */
-#ifdef HAVE_ARCH_MMU_GATHER
- struct arch_mmu_gather arch;
-#endif
struct page **pages;
struct page *local[8];
+
+#ifdef HAVE_ARCH_RCU_TABLE_FREE
+ struct mmu_table_batch *batch;
+#endif
};
static inline void __tlb_alloc_pages(struct mmu_gather *tlb)
@@ -72,8 +116,8 @@ tlb_gather_mmu(struct mmu_gather *tlb, s
tlb->fullmm = full_mm_flush;
-#ifdef HAVE_ARCH_MMU_GATHER
- tlb->arch = ARCH_MMU_GATHER_INIT;
+#ifdef HAVE_ARCH_RCU_TABLE_FREE
+ tlb->batch = NULL;
#endif
}
@@ -84,6 +128,9 @@ tlb_flush_mmu(struct mmu_gather *tlb, un
return;
tlb->need_flush = 0;
tlb_flush(tlb);
+#ifdef HAVE_ARCH_RCU_TABLE_FREE
+ tlb_table_flush(tlb);
+#endif
if (!tlb_fast_mode(tlb)) {
free_pages_and_swap_cache(tlb->pages, tlb->nr);
tlb->nr = 0;
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c
+++ linux-2.6/mm/memory.c
@@ -193,6 +193,87 @@ static void check_sync_rss_stat(struct t
#endif
+#ifdef HAVE_ARCH_RCU_TABLE_FREE
+
+/*
+ * See the comment near struct mmu_table_batch.
+ */
+
+static void tlb_remove_table_smp_sync(void *arg)
+{
+ /* Simply deliver the interrupt */
+}
+
+static void tlb_remove_table_one(void *table)
+{
+ /*
+ * This isn't an RCU grace period and hence the page-tables cannot be
+ * assumed to be actually RCU-freed.
+ *
+ * It is however sufficient for gup_fast() implementations that rely on
+ * IRQ disabling. See the comment near struct mmu_table_batch.
+ *
+ * [ Using synchronize_rcu() instead of this smp_call_function() would
+ * make it proper RCU, however that is also much slower ]
+ */
+ smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
+ __tlb_remove_table(table);
+}
+
+static void tlb_remove_table_rcu(struct rcu_head *head)
+{
+ struct mmu_table_batch *batch;
+ int i;
+
+ batch = container_of(head, struct mmu_table_batch, rcu);
+
+ for (i = 0; i < batch->nr; i++)
+ __tlb_remove_table(batch->tables[i]);
+
+ free_page((unsigned long)batch);
+}
+
+void tlb_table_flush(struct mmu_gather *tlb)
+{
+ struct mmu_table_batch **batch = &tlb->batch;
+
+ if (*batch) {
+ INIT_RCU_HEAD(&(*batch)->rcu);
+ call_rcu(&(*batch)->rcu, tlb_remove_table_rcu);
+ *batch = NULL;
+ }
+}
+
+void tlb_remove_table(struct mmu_gather *tlb, void *table)
+{
+ struct mmu_table_batch **batch = &tlb->batch;
+
+ tlb->need_flush = 1;
+
+ /*
+ * When there's less that two users of this mm there cannot be a
+ * concurrent gup_fast() lookup.
+ */
+ if (atomic_read(&tlb->mm->mm_users) < 2) {
+ __tlb_remove_table(table);
+ return;
+ }
+
+ if (*batch == NULL) {
+ *batch = (struct mmu_table_batch *)__get_free_page(GFP_ATOMIC);
+ if (*batch == NULL) {
+ tlb_remove_table_one(table);
+ return;
+ }
+ (*batch)->nr = 0;
+ }
+ (*batch)->tables[(*batch)->nr++] = table;
+ if ((*batch)->nr == MAX_TABLE_BATCH)
+ tlb_table_flush(tlb);
+}
+
+#endif
+
/*
* If a p?d_bad entry is found while walking page tables, report
* the error, before resetting entry to p?d_none. Usually (but
next prev parent reply other threads:[~2010-04-08 19:32 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-08 19:17 [PATCH 00/13] mm: preemptibility -v2 Peter Zijlstra
2010-04-08 19:17 ` [PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast() implementation Peter Zijlstra
2010-04-08 20:31 ` Rik van Riel
2010-04-09 3:11 ` Nick Piggin
2010-04-13 1:05 ` Benjamin Herrenschmidt
2010-04-13 3:43 ` Paul E. McKenney
2010-04-14 13:51 ` Peter Zijlstra
2010-04-15 14:28 ` Paul E. McKenney
2010-04-16 6:54 ` Benjamin Herrenschmidt
2010-04-16 13:43 ` Paul E. McKenney
2010-04-16 23:25 ` Benjamin Herrenschmidt
2010-04-16 13:51 ` Peter Zijlstra
2010-04-16 14:17 ` Paul E. McKenney
2010-04-16 14:23 ` Peter Zijlstra
2010-04-16 14:32 ` Paul E. McKenney
2010-04-16 14:56 ` Peter Zijlstra
2010-04-16 15:09 ` Paul E. McKenney
2010-04-16 15:14 ` Peter Zijlstra
2010-04-16 16:45 ` Paul E. McKenney
2010-04-16 19:37 ` Peter Zijlstra
2010-04-16 20:28 ` Paul E. McKenney
2010-04-18 3:06 ` James Bottomley
2010-04-18 13:55 ` Paul E. McKenney
2010-04-18 18:55 ` James Bottomley
2010-04-16 6:51 ` Benjamin Herrenschmidt
2010-04-16 8:18 ` Nick Piggin
2010-04-16 8:29 ` Benjamin Herrenschmidt
2010-04-16 9:22 ` Nick Piggin
2010-04-08 19:17 ` [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma() Peter Zijlstra
2010-04-08 20:50 ` Rik van Riel
2010-04-08 21:20 ` Andrew Morton
2010-04-08 21:54 ` Peter Zijlstra
2010-04-09 2:19 ` KOSAKI Motohiro
2010-04-09 2:19 ` Minchan Kim
2010-04-09 3:16 ` Nick Piggin
2010-04-09 4:56 ` KAMEZAWA Hiroyuki
2010-04-09 6:34 ` KOSAKI Motohiro
2010-04-09 6:47 ` KAMEZAWA Hiroyuki
2010-04-09 7:29 ` KOSAKI Motohiro
2010-04-09 7:57 ` KAMEZAWA Hiroyuki
2010-04-09 8:03 ` KAMEZAWA Hiroyuki
2010-04-09 8:24 ` KAMEZAWA Hiroyuki
2010-04-09 8:01 ` Minchan Kim
2010-04-09 8:17 ` KOSAKI Motohiro
2010-04-09 14:41 ` mlock and pageout race? Minchan Kim
2010-04-09 8:44 ` [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma() Peter Zijlstra
2010-05-24 19:32 ` Andrew Morton
2010-05-25 9:01 ` Peter Zijlstra
2010-04-09 12:57 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 03/13] x86: Remove last traces of quicklist usage Peter Zijlstra
2010-04-08 20:51 ` Rik van Riel
2010-04-08 19:17 ` [PATCH 04/13] mm: Move anon_vma ref out from under CONFIG_KSM Peter Zijlstra
2010-04-09 12:35 ` Rik van Riel
2010-04-08 19:17 ` [PATCH 05/13] mm: Make use of the anon_vma ref count Peter Zijlstra
2010-04-09 7:04 ` Christian Ehrhardt
2010-04-09 9:57 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 06/13] mm: Preemptible mmu_gather Peter Zijlstra
2010-04-09 3:25 ` Nick Piggin
2010-04-09 8:18 ` Peter Zijlstra
2010-04-09 20:36 ` Peter Zijlstra
2010-04-19 19:16 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 07/13] powerpc: " Peter Zijlstra
2010-04-09 4:07 ` Nick Piggin
2010-04-09 8:14 ` Peter Zijlstra
2010-04-09 8:46 ` Nick Piggin
2010-04-09 9:22 ` Peter Zijlstra
2010-04-13 2:06 ` Benjamin Herrenschmidt
2010-04-13 1:56 ` Benjamin Herrenschmidt
2010-04-13 1:23 ` Benjamin Herrenschmidt
2010-04-13 10:22 ` Peter Zijlstra
2010-04-14 13:34 ` Peter Zijlstra
2010-04-14 13:51 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 08/13] sparc: " Peter Zijlstra
2010-04-08 19:17 ` Peter Zijlstra [this message]
2010-04-09 3:35 ` [PATCH 09/13] mm, powerpc: Move the RCU page-table freeing into generic code Nick Piggin
2010-04-09 8:08 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 10/13] lockdep, mutex: Provide mutex_lock_nest_lock Peter Zijlstra
2010-04-09 15:36 ` Rik van Riel
2010-04-08 19:17 ` [PATCH 11/13] mutex: Provide mutex_is_contended Peter Zijlstra
2010-04-09 15:37 ` Rik van Riel
2010-04-08 19:17 ` [PATCH 12/13] mm: Convert i_mmap_lock and anon_vma->lock to mutexes Peter Zijlstra
2010-04-08 19:17 ` [PATCH 13/13] mm: Optimize page_lock_anon_vma Peter Zijlstra
2010-04-08 22:18 ` Paul E. McKenney
2010-04-09 8:35 ` Peter Zijlstra
2010-04-09 19:22 ` Paul E. McKenney
2010-04-08 20:29 ` [PATCH 00/13] mm: preemptibility -v2 David Miller
2010-04-08 20:35 ` Peter Zijlstra
2010-04-09 1:00 ` David Miller
2010-04-09 4:14 ` Nick Piggin
2010-04-09 8:35 ` Peter Zijlstra
2010-04-09 8:50 ` Nick Piggin
2010-04-09 8:58 ` Peter Zijlstra
2010-04-09 8:58 ` Martin Schwidefsky
2010-04-09 9:53 ` Peter Zijlstra
2010-04-09 9:03 ` David Howells
2010-04-09 9:22 ` Peter Zijlstra
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