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. Requested-by: David Miller Cc: Benjamin Herrenschmidt Signed-off-by: Peter Zijlstra --- 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 | 57 +++++++++++++++++++-- mm/memory.c | 77 +++++++++++++++++++++++++++++ 10 files changed, 151 insertions(+), 125 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 +31,29 @@ 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, 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 @@ -33,104 +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; 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 @@ -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); } /* 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 @@ -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 patch of page pointers * to work on, then just handle a few from the on-stack structure. @@ -44,11 +87,12 @@ 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[MMU_GATHER_BUNDLE]; + +#ifdef CONFIG_HAVE_RCU_TABLE_FREE + struct mmu_table_batch *batch; +#endif }; static inline void __tlb_alloc_page(struct mmu_gather *tlb) @@ -80,8 +124,8 @@ 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 CONFIG_HAVE_RCU_TABLE_FREE + tlb->batch = NULL; #endif } @@ -92,6 +136,9 @@ 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; Index: linux-2.6/mm/memory.c =================================================================== --- linux-2.6.orig/mm/memory.c +++ linux-2.6/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 Index: linux-2.6/arch/Kconfig =================================================================== --- linux-2.6.orig/arch/Kconfig +++ linux-2.6/arch/Kconfig @@ -178,4 +178,7 @@ config HAVE_ARCH_JUMP_LABEL config HAVE_ARCH_MUTEX_CPU_RELAX bool +config HAVE_RCU_TABLE_FREE + bool + source "kernel/gcov/Kconfig" Index: linux-2.6/arch/powerpc/Kconfig =================================================================== --- linux-2.6.orig/arch/powerpc/Kconfig +++ linux-2.6/arch/powerpc/Kconfig @@ -134,6 +134,7 @@ config PPC select HAVE_GENERIC_HARDIRQS select HAVE_SPARSE_IRQ select IRQ_PER_CPU + select HAVE_RCU_TABLE_FREE if SMP config EARLY_PRINTK bool -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/