[PATCH 06/13] mm: Preemptible mmu_gather

Peter Zijlstra
2010-04-08T19:17:43Z

[-- Attachment #1: mm-preempt-tlb-gather.patch --]
[-- Type: text/plain, Size: 9826 bytes --]

Make mmu_gather preemptible by using a small on stack list and use
an option allocation to speed things up.

This breaks at least PPC for which there is a patch in -rt which
still needs porting.

Preemptible mmu_gather is desired in general and usable once
i_mmap_lock becomes a mutex. Doing it before the mutex conversion
saves us from having to rework the code by moving the mmu_gather
bits inside the i_mmap_lock.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
fs/exec.c | 10 ++++-----
include/asm-generic/tlb.h | 51 +++++++++++++++++++++++++++++-----------------
include/linux/mm.h | 2 -
mm/memory.c | 27 +++++-------------------
mm/mmap.c | 16 +++++++-------
5 files changed, 53 insertions(+), 53 deletions(-)

Index: linux-2.6/fs/exec.c
===================================================================
--- linux-2.6.orig/fs/exec.c
+++ linux-2.6/fs/exec.c
@@ -503,7 +503,7 @@ static int shift_arg_pages(struct vm_are
unsigned long length = old_end - old_start;
unsigned long new_start = old_start - shift;
unsigned long new_end = old_end - shift;
- struct mmu_gather *tlb;
+ struct mmu_gather tlb;

BUG_ON(new_start > new_end);

@@ -529,12 +529,12 @@ static int shift_arg_pages(struct vm_are
return -ENOMEM;

lru_add_drain();
- tlb = tlb_gather_mmu(mm, 0);
+ tlb_gather_mmu(&tlb, mm, 0);
if (new_end > old_start) {
/*
* when the old and new regions overlap clear from new_end.
*/
- free_pgd_range(tlb, new_end, old_end, new_end,
+ free_pgd_range(&tlb, new_end, old_end, new_end,
vma->vm_next ? vma->vm_next->vm_start : 0);
} else {
/*
@@ -543,10 +543,10 @@ static int shift_arg_pages(struct vm_are
* have constraints on va-space that make this illegal (IA64) -
* for the others its just a little faster.
*/
- free_pgd_range(tlb, old_start, old_end, new_end,
+ free_pgd_range(&tlb, old_start, old_end, new_end,
vma->vm_next ? vma->vm_next->vm_start : 0);
}
- tlb_finish_mmu(tlb, new_end, old_end);
+ tlb_finish_mmu(&tlb, new_end, old_end);

/*
* Shrink the vma to just the new range. Always succeeds.
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
@@ -22,14 +22,8 @@
* and page free order so much..
*/
#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
#endif

@@ -39,30 +33,48 @@
struct mmu_gather {
struct mm_struct *mm;
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 */
- struct page * pages[FREE_PTE_NR];
+#ifdef HAVE_ARCH_MMU_GATHER
+ struct arch_mmu_gather arch;
+#endif
+ struct page **pages;
+ struct page *local[8];
};

-/* Users of the generic TLB shootdown code must declare this storage space. */
-DECLARE_PER_CPU(struct mmu_gather, mmu_gathers);
+static inline void __tlb_alloc_pages(struct mmu_gather *tlb)
+{
+ unsigned long addr = __get_free_pages(GFP_ATOMIC, 0);
+
+ if (addr) {
+ tlb->pages = (void *)addr;
+ tlb->max = PAGE_SIZE / sizeof(struct page *);
+ }
+}

/* tlb_gather_mmu
* Return a pointer to an initialized struct mmu_gather.
*/
-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, unsigned int full_mm_flush)
{
- 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->max = ARRAY_SIZE(tlb->local);
+ tlb->pages = tlb->local;
+
+ if (num_online_cpus() > 1) {
+ tlb->nr = 0;
+ __tlb_alloc_pages(tlb);
+ } else /* Use fast mode if only one CPU is online */
+ tlb->nr = ~0U;

tlb->fullmm = full_mm_flush;

- return tlb;
+#ifdef HAVE_ARCH_MMU_GATHER
+ tlb->arch = ARCH_MMU_GATHER_INIT;
+#endif
}

static inline void
@@ -75,6 +87,8 @@ tlb_flush_mmu(struct mmu_gather *tlb, un
if (!tlb_fast_mode(tlb)) {
free_pages_and_swap_cache(tlb->pages, tlb->nr);
tlb->nr = 0;
+ if (tlb->pages == tlb->local)
+ __tlb_alloc_pages(tlb);
}
}

@@ -90,7 +104,8 @@ tlb_finish_mmu(struct mmu_gather *tlb, u
/* keep the page table cache within bounds */
check_pgt_cache();

- put_cpu_var(mmu_gathers);
+ if (tlb->pages != tlb->local)
+ free_pages((unsigned long)tlb->pages, 0);
}

/* tlb_remove_page
@@ -106,7 +121,7 @@ static inline void tlb_remove_page(struc
return;
}
tlb->pages[tlb->nr++] = page;
- if (tlb->nr >= FREE_PTE_NR)
+ if (tlb->nr >= tlb->max)
tlb_flush_mmu(tlb, 0, 0);
}

Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h
+++ linux-2.6/include/linux/mm.h
@@ -760,7 +760,7 @@ int zap_vma_ptes(struct vm_area_struct *
unsigned long size);
unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address,
unsigned long size, struct zap_details *);
-unsigned long unmap_vmas(struct mmu_gather **tlb,
+unsigned long unmap_vmas(struct mmu_gather *tlb,
struct vm_area_struct *start_vma, unsigned long start_addr,
unsigned long end_addr, unsigned long *nr_accounted,
struct zap_details *);
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c
+++ linux-2.6/mm/memory.c
@@ -1095,17 +1095,14 @@ static unsigned long unmap_page_range(st
* ensure that any thus-far unmapped pages are flushed before unmap_vmas()
* drops the lock and schedules.
*/
-unsigned long unmap_vmas(struct mmu_gather **tlbp,
+unsigned long unmap_vmas(struct mmu_gather *tlb,
struct vm_area_struct *vma, unsigned long start_addr,
unsigned long end_addr, unsigned long *nr_accounted,
struct zap_details *details)
{
long zap_work = ZAP_BLOCK_SIZE;
- unsigned long tlb_start = 0; /* For tlb_finish_mmu */
- int tlb_start_valid = 0;
unsigned long start = start_addr;
spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL;
- int fullmm = (*tlbp)->fullmm;
struct mm_struct *mm = vma->vm_mm;

mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
@@ -1126,11 +1123,6 @@ unsigned long unmap_vmas(struct mmu_gath
untrack_pfn_vma(vma, 0, 0);

while (start != end) {
- if (!tlb_start_valid) {
- tlb_start = start;
- tlb_start_valid = 1;
- }
-
if (unlikely(is_vm_hugetlb_page(vma))) {
/*
* It is undesirable to test vma->vm_file as it
@@ -1151,7 +1143,7 @@ unsigned long unmap_vmas(struct mmu_gath

start = end;
} else
- start = unmap_page_range(*tlbp, vma,
+ start = unmap_page_range(tlb, vma,
start, end, &zap_work, details);

if (zap_work > 0) {
@@ -1159,19 +1151,13 @@ unsigned long unmap_vmas(struct mmu_gath
break;
}

- tlb_finish_mmu(*tlbp, tlb_start, start);
-
if (need_resched() ||
(i_mmap_lock && spin_needbreak(i_mmap_lock))) {
- if (i_mmap_lock) {
- *tlbp = NULL;
+ if (i_mmap_lock)
goto out;
- }
cond_resched();
}

- *tlbp = tlb_gather_mmu(vma->vm_mm, fullmm);
- tlb_start_valid = 0;
zap_work = ZAP_BLOCK_SIZE;
}
}
@@ -1191,16 +1177,15 @@ unsigned long zap_page_range(struct vm_a
unsigned long size, struct zap_details *details)
{
struct mm_struct *mm = vma->vm_mm;
- struct mmu_gather *tlb;
+ struct mmu_gather tlb;
unsigned long end = address + size;
unsigned long nr_accounted = 0;

lru_add_drain();
- tlb = tlb_gather_mmu(mm, 0);
+ tlb_gather_mmu(&tlb, mm, 0);
update_hiwater_rss(mm);
end = unmap_vmas(&tlb, vma, address, end, &nr_accounted, details);
- if (tlb)
- tlb_finish_mmu(tlb, address, end);
+ tlb_finish_mmu(&tlb, address, end);
return end;
}

Index: linux-2.6/mm/mmap.c
===================================================================
--- linux-2.6.orig/mm/mmap.c
+++ linux-2.6/mm/mmap.c
@@ -1844,17 +1844,17 @@ static void unmap_region(struct mm_struc
unsigned long start, unsigned long end)
{
struct vm_area_struct *next = prev? prev->vm_next: mm->mmap;
- struct mmu_gather *tlb;
+ struct mmu_gather tlb;
unsigned long nr_accounted = 0;

lru_add_drain();
- tlb = tlb_gather_mmu(mm, 0);
+ tlb_gather_mmu(&tlb, mm, 0);
update_hiwater_rss(mm);
unmap_vmas(&tlb, vma, start, end, &nr_accounted, NULL);
vm_unacct_memory(nr_accounted);
- free_pgtables(tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,
+ free_pgtables(&tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,
next? next->vm_start: 0);
- tlb_finish_mmu(tlb, start, end);
+ tlb_finish_mmu(&tlb, start, end);
}

/*
@@ -2190,7 +2190,7 @@ EXPORT_SYMBOL(do_brk);
/* Release all mmaps. */
void exit_mmap(struct mm_struct *mm)
{
- struct mmu_gather *tlb;
+ struct mmu_gather tlb;
struct vm_area_struct *vma;
unsigned long nr_accounted = 0;
unsigned long end;
@@ -2215,14 +2215,14 @@ void exit_mmap(struct mm_struct *mm)

lru_add_drain();
flush_cache_mm(mm);
- tlb = tlb_gather_mmu(mm, 1);
+ tlb_gather_mmu(&tlb, mm, 1);
/* update_hiwater_rss(mm) here? but nobody should be looking */
/* Use -1 here to ensure all VMAs in the mm are unmapped */
end = unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL);
vm_unacct_memory(nr_accounted);

- free_pgtables(tlb, vma, FIRST_USER_ADDRESS, 0);
- tlb_finish_mmu(tlb, 0, end);
+ free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
+ tlb_finish_mmu(&tlb, 0, end);

/*
* Walk the list again, actually closing and freeing it,