The patch titled
mm, powerpc: move the RCU page-table freeing into generic code
has been added to the -mm tree. Its filename is
mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: mm, powerpc: move the RCU page-table freeing into generic code
From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
In case other architectures require RCU freed page-tables to implement
gup_fast() and software filled hashes and similar things, provide the
means to do so by moving the logic into generic code.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Requested-by: David Miller <davem@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Russell King <rmk@xxxxxxxxxxxxxxxx>
Cc: Paul Mundt <lethal@xxxxxxxxxxxx>
Cc: Jeff Dike <jdike@xxxxxxxxxxx>
Cc: Richard Weinberger <richard@xxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/Kconfig | 3
arch/powerpc/Kconfig | 1
arch/powerpc/include/asm/pgalloc.h | 21 ++++-
arch/powerpc/include/asm/tlb.h | 10 --
arch/powerpc/mm/pgtable.c | 98 ---------------------------
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 | 56 ++++++++++++++-
mm/memory.c | 77 +++++++++++++++++++++
10 files changed, 150 insertions(+), 125 deletions(-)
diff -puN arch/Kconfig~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code arch/Kconfig
--- a/arch/Kconfig~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/arch/Kconfig
@@ -175,4 +175,7 @@ config HAVE_ARCH_JUMP_LABEL
config HAVE_ARCH_MUTEX_CPU_RELAX
bool
+config HAVE_RCU_TABLE_FREE
+ bool
+
source "kernel/gcov/Kconfig"
diff -puN arch/powerpc/Kconfig~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code arch/powerpc/Kconfig
--- a/arch/powerpc/Kconfig~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/arch/powerpc/Kconfig
@@ -140,6 +140,7 @@ config PPC
select IRQ_PER_CPU
select GENERIC_IRQ_SHOW
select GENERIC_IRQ_SHOW_LEVEL
+ select HAVE_RCU_TABLE_FREE if SMP
config EARLY_PRINTK
bool
diff -puN arch/powerpc/include/asm/pgalloc.h~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code arch/powerpc/include/asm/pgalloc.h
--- a/arch/powerpc/include/asm/pgalloc.h~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/arch/powerpc/include/asm/pgalloc.h
@@ -31,14 +31,29 @@ 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);
+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,
diff -puN arch/powerpc/include/asm/tlb.h~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code arch/powerpc/include/asm/tlb.h
--- a/arch/powerpc/include/asm/tlb.h~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/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... */
diff -puN arch/powerpc/mm/pgtable.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code arch/powerpc/mm/pgtable.c
--- a/arch/powerpc/mm/pgtable.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/arch/powerpc/mm/pgtable.c
@@ -33,104 +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)
-{
- call_rcu_sched(&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;
-
- 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;
diff -puN arch/powerpc/mm/tlb_hash32.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code arch/powerpc/mm/tlb_hash32.c
--- a/arch/powerpc/mm/tlb_hash32.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/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);
}
/*
diff -puN arch/powerpc/mm/tlb_hash64.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code arch/powerpc/mm/tlb_hash64.c
--- a/arch/powerpc/mm/tlb_hash64.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/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);
}
/**
diff -puN arch/powerpc/mm/tlb_nohash.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code arch/powerpc/mm/tlb_nohash.c
--- a/arch/powerpc/mm/tlb_nohash.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/arch/powerpc/mm/tlb_nohash.c
@@ -299,9 +299,6 @@ 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);
}
/*
diff -puN include/asm-generic/tlb.h~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code include/asm-generic/tlb.h
--- a/include/asm-generic/tlb.h~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/include/asm-generic/tlb.h
@@ -29,6 +29,49 @@
#define tlb_fast_mode(tlb) 1
#endif
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+/*
+ * 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().
+ *
+ */
+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.
@@ -40,13 +83,13 @@
*/
struct mmu_gather {
struct mm_struct *mm;
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+ struct mmu_table_batch *batch;
+#endif
unsigned int nr; /* set to ~0U means fast mode */
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[MMU_GATHER_BUNDLE];
};
@@ -82,8 +125,8 @@ tlb_gather_mmu(struct mmu_gather *tlb, s
tlb->fullmm = fullmm;
-#ifdef HAVE_ARCH_MMU_GATHER
- tlb->arch = ARCH_MMU_GATHER_INIT;
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+ tlb->batch = NULL;
#endif
}
@@ -94,6 +137,9 @@ tlb_flush_mmu(struct mmu_gather *tlb)
return;
tlb->need_flush = 0;
tlb_flush(tlb);
+#ifdef CONFIG_HAVE_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;
diff -puN mm/memory.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code mm/memory.c
--- a/mm/memory.c~mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code
+++ a/mm/memory.c
@@ -193,6 +193,83 @@ static void check_sync_rss_stat(struct t
#endif
+#ifdef CONFIG_HAVE_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 software page-table walkers that rely on
+ * IRQ disabling. See the comment near struct mmu_table_batch.
+ */
+ 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) {
+ call_rcu_sched(&(*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 then two users of this mm there cannot be a
+ * concurrent page-table walk.
+ */
+ 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_NOWAIT | __GFP_NOWARN);
+ 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
_
Patches currently in -mm which might be from a.p.zijlstra@xxxxxxxxx are
linux-next.patch
net-convert-%p-usage-to-%pk.patch
mm-mmu_gather-rework.patch
mm-mmu_gather-rework-fix.patch
powerpc-mmu_gather-rework.patch
sparc-mmu_gather-rework.patch
s390-mmu_gather-rework.patch
arm-mmu_gather-rework.patch
sh-mmu_gather-rework.patch
ia64-mmu_gather-rework.patch
um-mmu_gather-rework.patch
mm-now-that-all-old-mmu_gather-code-is-gone-remove-the-storage.patch
mm-powerpc-move-the-rcu-page-table-freeing-into-generic-code.patch
mm-extended-batches-for-generic-mmu_gather.patch
lockdep-mutex-provide-mutex_lock_nest_lock.patch
mm-remove-i_mmap_lock-lockbreak.patch
mm-convert-i_mmap_lock-to-a-mutex.patch
mm-revert-page_lock_anon_vma-lock-annotation.patch
mm-improve-page_lock_anon_vma-comment.patch
mm-use-refcounts-for-page_lock_anon_vma.patch
mm-convert-anon_vma-lock-to-a-mutex.patch
mm-optimize-page_lock_anon_vma-fast-path.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
