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SubjectRe: [PATCH 00/21] mm: Preemptibility -v6
On Tue, 15 Feb 2011 15:00:17 +0100
Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:

> On Wed, 19 Jan 2011 18:10:39 +0100
> Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
>
> > Martin, while doing the below DEFINE_PER_CPU removal I saw you had a
> > bunch of RCU table removal thingies in arch/s390/mm/pgtable.c, could
> > s390 use the generic bits like sparc and powerpc (see patch 16)?
>
> That should do it. 229 deletions vs. 74 insertions, not bad. And the
> tlb flushing code actually got simpler. Even better :-)

Darn, forgot "quilt refresh". The last patch I've sent is the old,
broken one. This one is better..

--
Subject: [PATCH] s390: use generic RCP page-table freeing

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

Now that we have a generic implementation for RCU based page table
freeing, use it for s390 as well. It saves a couple of lines.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
arch/s390/Kconfig | 1
arch/s390/include/asm/pgalloc.h | 19 +--
arch/s390/include/asm/tlb.h | 91 ++++++++----------
arch/s390/mm/pgtable.c | 192 +++++-----------------------------------
4 files changed, 74 insertions(+), 229 deletions(-)

--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -87,6 +87,7 @@ config S390
select HAVE_KERNEL_LZO
select HAVE_GET_USER_PAGES_FAST
select HAVE_ARCH_MUTEX_CPU_RELAX
+ select HAVE_RCU_TABLE_FREE
select ARCH_INLINE_SPIN_TRYLOCK
select ARCH_INLINE_SPIN_TRYLOCK_BH
select ARCH_INLINE_SPIN_LOCK
--- a/arch/s390/include/asm/pgalloc.h
+++ b/arch/s390/include/asm/pgalloc.h
@@ -20,12 +20,11 @@
#define check_pgt_cache() do {} while (0)

unsigned long *crst_table_alloc(struct mm_struct *, int);
-void crst_table_free(struct mm_struct *, unsigned long *);
-void crst_table_free_rcu(struct mm_struct *, unsigned long *);
+void crst_table_free(unsigned long *);

unsigned long *page_table_alloc(struct mm_struct *);
-void page_table_free(struct mm_struct *, unsigned long *);
-void page_table_free_rcu(struct mm_struct *, unsigned long *);
+void page_table_free(unsigned long *);
+
void disable_noexec(struct mm_struct *, struct task_struct *);

static inline void clear_table(unsigned long *s, unsigned long val, size_t n)
@@ -95,7 +94,7 @@ static inline pud_t *pud_alloc_one(struc
crst_table_init(table, _REGION3_ENTRY_EMPTY);
return (pud_t *) table;
}
-#define pud_free(mm, pud) crst_table_free(mm, (unsigned long *) pud)
+#define pud_free(mm, pud) crst_table_free((unsigned long *) pud)

static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long vmaddr)
{
@@ -104,7 +103,7 @@ static inline pmd_t *pmd_alloc_one(struc
crst_table_init(table, _SEGMENT_ENTRY_EMPTY);
return (pmd_t *) table;
}
-#define pmd_free(mm, pmd) crst_table_free(mm, (unsigned long *) pmd)
+#define pmd_free(mm, pmd) crst_table_free((unsigned long *) pmd)

static inline void pgd_populate_kernel(struct mm_struct *mm,
pgd_t *pgd, pud_t *pud)
@@ -148,7 +147,7 @@ static inline pgd_t *pgd_alloc(struct mm
return (pgd_t *)
crst_table_alloc(mm, user_mode == SECONDARY_SPACE_MODE);
}
-#define pgd_free(mm, pgd) crst_table_free(mm, (unsigned long *) pgd)
+#define pgd_free(mm, pgd) crst_table_free((unsigned long *) pgd)

static inline void pmd_populate_kernel(struct mm_struct *mm,
pmd_t *pmd, pte_t *pte)
@@ -175,9 +174,7 @@ static inline void pmd_populate(struct m
#define pte_alloc_one_kernel(mm, vmaddr) ((pte_t *) page_table_alloc(mm))
#define pte_alloc_one(mm, vmaddr) ((pte_t *) page_table_alloc(mm))

-#define pte_free_kernel(mm, pte) page_table_free(mm, (unsigned long *) pte)
-#define pte_free(mm, pte) page_table_free(mm, (unsigned long *) pte)
-
-extern void rcu_table_freelist_finish(void);
+#define pte_free_kernel(mm, pte) page_table_free((unsigned long *) pte)
+#define pte_free(mm, pte) page_table_free((unsigned long *) pte)

#endif /* _S390_PGALLOC_H */
--- a/arch/s390/include/asm/tlb.h
+++ b/arch/s390/include/asm/tlb.h
@@ -29,50 +29,42 @@
#include <asm/smp.h>
#include <asm/tlbflush.h>

+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 *))
+
+void tlb_table_flush(struct mmu_gather *);
+void tlb_remove_table(struct mmu_gather *, void *);
+
struct mmu_gather {
struct mm_struct *mm;
unsigned int fullmm;
- unsigned int nr_ptes;
- unsigned int nr_pxds;
- unsigned int max;
- void **array;
- void *local[8];
+ struct mmu_table_batch *batch;
+ /* need_flush is used only for page tables */
+ unsigned int need_flush : 1;
};

-static inline void __tlb_alloc_page(struct mmu_gather *tlb)
-{
- unsigned long addr = __get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
-
- if (addr) {
- tlb->array = (void *) addr;
- tlb->max = PAGE_SIZE / sizeof(void *);
- }
-}
-
static inline void tlb_gather_mmu(struct mmu_gather *tlb,
struct mm_struct *mm,
unsigned int full_mm_flush)
{
tlb->mm = mm;
- tlb->max = ARRAY_SIZE(tlb->local);
- tlb->array = tlb->local;
tlb->fullmm = full_mm_flush;
if (tlb->fullmm)
__tlb_flush_mm(mm);
- else
- __tlb_alloc_page(tlb);
- tlb->nr_ptes = 0;
- tlb->nr_pxds = tlb->max;
+ tlb->batch = NULL;
+ tlb->need_flush = 0;
}

static inline void tlb_flush_mmu(struct mmu_gather *tlb)
{
- if (!tlb->fullmm && (tlb->nr_ptes > 0 || tlb->nr_pxds < tlb->max))
- __tlb_flush_mm(tlb->mm);
- while (tlb->nr_ptes > 0)
- page_table_free_rcu(tlb->mm, tlb->array[--tlb->nr_ptes]);
- while (tlb->nr_pxds < tlb->max)
- crst_table_free_rcu(tlb->mm, tlb->array[tlb->nr_pxds++]);
+ if (tlb->need_flush)
+ tlb_table_flush(tlb);
}

static inline void tlb_finish_mmu(struct mmu_gather *tlb,
@@ -80,13 +72,8 @@ static inline void tlb_finish_mmu(struct
{
tlb_flush_mmu(tlb);

- rcu_table_freelist_finish();
-
/* keep the page table cache within bounds */
check_pgt_cache();
-
- if (tlb->array != tlb->local)
- free_pages((unsigned long) tlb->array, 0);
}

/*
@@ -113,12 +100,11 @@ static inline void tlb_remove_page(struc
static inline void pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
unsigned long address)
{
- if (!tlb->fullmm) {
- tlb->array[tlb->nr_ptes++] = pte;
- if (tlb->nr_ptes >= tlb->nr_pxds)
- tlb_flush_mmu(tlb);
- } else
- page_table_free(tlb->mm, (unsigned long *) pte);
+ if (!tlb->fullmm)
+ /* Use LSB to distinguish crst table vs. page table */
+ tlb_remove_table(tlb, (void *) pte + 1);
+ else
+ page_table_free((unsigned long *) pte);
}

/*
@@ -134,12 +120,10 @@ static inline void pmd_free_tlb(struct m
#ifdef __s390x__
if (tlb->mm->context.asce_limit <= (1UL << 31))
return;
- if (!tlb->fullmm) {
- tlb->array[--tlb->nr_pxds] = pmd;
- if (tlb->nr_ptes >= tlb->nr_pxds)
- tlb_flush_mmu(tlb);
- } else
- crst_table_free(tlb->mm, (unsigned long *) pmd);
+ if (!tlb->fullmm)
+ tlb_remove_table(tlb, pmd);
+ else
+ crst_table_free((unsigned long *) pmd);
#endif
}

@@ -156,15 +140,22 @@ static inline void pud_free_tlb(struct m
#ifdef __s390x__
if (tlb->mm->context.asce_limit <= (1UL << 42))
return;
- if (!tlb->fullmm) {
- tlb->array[--tlb->nr_pxds] = pud;
- if (tlb->nr_ptes >= tlb->nr_pxds)
- tlb_flush_mmu(tlb);
- } else
- crst_table_free(tlb->mm, (unsigned long *) pud);
+ if (!tlb->fullmm)
+ tlb_remove_table(tlb, pud);
+ else
+ crst_table_free((unsigned long *) pud);
#endif
}

+static inline void __tlb_remove_table(void *table)
+{
+ /* Use LSB to distinguish crst table vs. page table */
+ if ((unsigned long) table & 1)
+ page_table_free(table - 1);
+ else
+ crst_table_free(table);
+}
+
#define tlb_start_vma(tlb, vma) do { } while (0)
#define tlb_end_vma(tlb, vma) do { } while (0)
#define tlb_remove_tlb_entry(tlb, ptep, addr) do { } while (0)
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -24,92 +24,17 @@
#include <asm/tlbflush.h>
#include <asm/mmu_context.h>

-struct rcu_table_freelist {
- struct rcu_head rcu;
- struct mm_struct *mm;
- unsigned int pgt_index;
- unsigned int crst_index;
- unsigned long *table[0];
-};
-
-#define RCU_FREELIST_SIZE \
- ((PAGE_SIZE - sizeof(struct rcu_table_freelist)) \
- / sizeof(unsigned long))
-
-static DEFINE_PER_CPU(struct rcu_table_freelist *, rcu_table_freelist);
-
-static void __page_table_free(struct mm_struct *mm, unsigned long *table);
-static void __crst_table_free(struct mm_struct *mm, unsigned long *table);
-
-static struct rcu_table_freelist *rcu_table_freelist_get(struct mm_struct *mm)
-{
- struct rcu_table_freelist **batchp = &__get_cpu_var(rcu_table_freelist);
- struct rcu_table_freelist *batch = *batchp;
-
- if (batch)
- return batch;
- batch = (struct rcu_table_freelist *) __get_free_page(GFP_ATOMIC);
- if (batch) {
- batch->mm = mm;
- batch->pgt_index = 0;
- batch->crst_index = RCU_FREELIST_SIZE;
- *batchp = batch;
- }
- return batch;
-}
-
-static void rcu_table_freelist_callback(struct rcu_head *head)
-{
- struct rcu_table_freelist *batch =
- container_of(head, struct rcu_table_freelist, rcu);
-
- while (batch->pgt_index > 0)
- __page_table_free(batch->mm, batch->table[--batch->pgt_index]);
- while (batch->crst_index < RCU_FREELIST_SIZE)
- __crst_table_free(batch->mm, batch->table[batch->crst_index++]);
- free_page((unsigned long) batch);
-}
-
-void rcu_table_freelist_finish(void)
-{
- struct rcu_table_freelist *batch = __get_cpu_var(rcu_table_freelist);
-
- if (!batch)
- return;
- call_rcu(&batch->rcu, rcu_table_freelist_callback);
- __get_cpu_var(rcu_table_freelist) = NULL;
-}
-
-static void smp_sync(void *arg)
-{
-}

#ifndef CONFIG_64BIT
#define ALLOC_ORDER 1
#define TABLES_PER_PAGE 4
#define FRAG_MASK 15UL
#define SECOND_HALVES 10UL
-
-void clear_table_pgstes(unsigned long *table)
-{
- clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/4);
- memset(table + 256, 0, PAGE_SIZE/4);
- clear_table(table + 512, _PAGE_TYPE_EMPTY, PAGE_SIZE/4);
- memset(table + 768, 0, PAGE_SIZE/4);
-}
-
#else
#define ALLOC_ORDER 2
#define TABLES_PER_PAGE 2
#define FRAG_MASK 3UL
#define SECOND_HALVES 2UL
-
-void clear_table_pgstes(unsigned long *table)
-{
- clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/2);
- memset(table + 256, 0, PAGE_SIZE/2);
-}
-
#endif

unsigned long VMALLOC_START = VMALLOC_END - VMALLOC_SIZE;
@@ -138,6 +63,7 @@ unsigned long *crst_table_alloc(struct m
return NULL;
}
page->index = page_to_phys(shadow);
+ page->private = (unsigned long) mm;
}
spin_lock_bh(&mm->context.list_lock);
list_add(&page->lru, &mm->context.crst_list);
@@ -145,47 +71,19 @@ unsigned long *crst_table_alloc(struct m
return (unsigned long *) page_to_phys(page);
}

-static void __crst_table_free(struct mm_struct *mm, unsigned long *table)
-{
- unsigned long *shadow = get_shadow_table(table);
-
- if (shadow)
- free_pages((unsigned long) shadow, ALLOC_ORDER);
- free_pages((unsigned long) table, ALLOC_ORDER);
-}
-
-void crst_table_free(struct mm_struct *mm, unsigned long *table)
-{
- struct page *page = virt_to_page(table);
-
- spin_lock_bh(&mm->context.list_lock);
- list_del(&page->lru);
- spin_unlock_bh(&mm->context.list_lock);
- __crst_table_free(mm, table);
-}
-
-void crst_table_free_rcu(struct mm_struct *mm, unsigned long *table)
+void crst_table_free(unsigned long *table)
{
- struct rcu_table_freelist *batch;
struct page *page = virt_to_page(table);
+ struct mm_struct *mm = (struct mm_struct *) page->private;
+ unsigned long *shadow = get_shadow_table(table);

spin_lock_bh(&mm->context.list_lock);
list_del(&page->lru);
+ page->private = 0;
spin_unlock_bh(&mm->context.list_lock);
- if (atomic_read(&mm->mm_users) < 2 &&
- cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
- __crst_table_free(mm, table);
- return;
- }
- batch = rcu_table_freelist_get(mm);
- if (!batch) {
- smp_call_function(smp_sync, NULL, 1);
- __crst_table_free(mm, table);
- return;
- }
- batch->table[--batch->crst_index] = table;
- if (batch->pgt_index >= batch->crst_index)
- rcu_table_freelist_finish();
+ if (shadow)
+ free_pages((unsigned long) shadow, ALLOC_ORDER);
+ free_pages((unsigned long) table, ALLOC_ORDER);
}

#ifdef CONFIG_64BIT
@@ -223,7 +121,7 @@ repeat:
}
spin_unlock_bh(&mm->page_table_lock);
if (table)
- crst_table_free(mm, table);
+ crst_table_free(table);
if (mm->context.asce_limit < limit)
goto repeat;
update_mm(mm, current);
@@ -257,7 +155,7 @@ void crst_table_downgrade(struct mm_stru
}
mm->pgd = (pgd_t *) (pgd_val(*pgd) & _REGION_ENTRY_ORIGIN);
mm->task_size = mm->context.asce_limit;
- crst_table_free(mm, (unsigned long *) pgd);
+ crst_table_free((unsigned long *) pgd);
}
update_mm(mm, current);
}
@@ -288,11 +186,7 @@ unsigned long *page_table_alloc(struct m
return NULL;
pgtable_page_ctor(page);
page->flags &= ~FRAG_MASK;
- table = (unsigned long *) page_to_phys(page);
- if (mm->context.has_pgste)
- clear_table_pgstes(table);
- else
- clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE);
+ page->private = (unsigned long) mm;
spin_lock_bh(&mm->context.list_lock);
list_add(&page->lru, &mm->context.pgtable_list);
}
@@ -305,42 +199,34 @@ unsigned long *page_table_alloc(struct m
if ((page->flags & FRAG_MASK) == ((1UL << TABLES_PER_PAGE) - 1))
list_move_tail(&page->lru, &mm->context.pgtable_list);
spin_unlock_bh(&mm->context.list_lock);
+ clear_table(table, _PAGE_TYPE_EMPTY, PTRS_PER_PTE * sizeof(long));
+ if (mm->context.noexec)
+ clear_table(table + 256, _PAGE_TYPE_EMPTY,
+ PTRS_PER_PTE * sizeof(long));
+ else if (mm->context.has_pgste)
+ clear_table(table + 256, 0, PTRS_PER_PTE * sizeof(long));
return table;
}

-static void __page_table_free(struct mm_struct *mm, unsigned long *table)
+void page_table_free(unsigned long *table)
{
- struct page *page;
- unsigned long bits;
-
- bits = ((unsigned long) table) & 15;
- table = (unsigned long *)(((unsigned long) table) ^ bits);
- page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
- page->flags ^= bits;
- if (!(page->flags & FRAG_MASK)) {
- pgtable_page_dtor(page);
- __free_page(page);
- }
-}
-
-void page_table_free(struct mm_struct *mm, unsigned long *table)
-{
- struct page *page;
+ struct page *page = virt_to_page(table);
+ struct mm_struct *mm = (struct mm_struct *) page->private;
unsigned long bits;

bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
- page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
spin_lock_bh(&mm->context.list_lock);
page->flags ^= bits;
if (page->flags & FRAG_MASK) {
/* Page now has some free pgtable fragments. */
- if (!list_empty(&page->lru))
- list_move(&page->lru, &mm->context.pgtable_list);
+ list_move(&page->lru, &mm->context.pgtable_list);
page = NULL;
- } else
+ } else {
/* All fragments of the 4K page have been freed. */
list_del(&page->lru);
+ page->private = 0;
+ }
spin_unlock_bh(&mm->context.list_lock);
if (page) {
pgtable_page_dtor(page);
@@ -348,36 +234,6 @@ void page_table_free(struct mm_struct *m
}
}

-void page_table_free_rcu(struct mm_struct *mm, unsigned long *table)
-{
- struct rcu_table_freelist *batch;
- struct page *page;
- unsigned long bits;
-
- if (atomic_read(&mm->mm_users) < 2 &&
- cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
- page_table_free(mm, table);
- return;
- }
- batch = rcu_table_freelist_get(mm);
- if (!batch) {
- smp_call_function(smp_sync, NULL, 1);
- page_table_free(mm, table);
- return;
- }
- bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
- bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
- page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
- spin_lock_bh(&mm->context.list_lock);
- /* Delayed freeing with rcu prevents reuse of pgtable fragments */
- list_del_init(&page->lru);
- spin_unlock_bh(&mm->context.list_lock);
- table = (unsigned long *)(((unsigned long) table) | bits);
- batch->table[batch->pgt_index++] = table;
- if (batch->pgt_index >= batch->crst_index)
- rcu_table_freelist_finish();
-}
-
void disable_noexec(struct mm_struct *mm, struct task_struct *tsk)
{
struct page *page;
--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.



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