Re: [PATCH 00/13] mm: preemptibility -v2

Martin Schwidefsky
2010-04-09T08:58:05Z

Hi Peter,

On Thu, 08 Apr 2010 21:17:37 +0200
Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> The side-effects are that we can finally make mmu_gather preemptible, something
> which lots of people have wanted to do for a long time.

Yes, that is a good thing. With the preemptible mmu_gather s390 will
use less IDTEs (that is the instruction that flushes all TLBs for a
given address space) on a full flush. Good :-)

> This patch-set seems to build and boot on my x86_64 machines and even builds a
> kernel. I've also attempted powerpc and sparc, which I've compile tested with
> their respective defconfigs, remaining are (afaikt the rest uses the generic
> tlb bits):
>
> - s390
> - ia64
> - arm
> - superh
> - um
>
> From those, s390 and ia64 look 'interesting', arm and superh seem very similar
> and should be relatively easy (-rt has a patchlet for arm iirc).

To get the 'interesting' TLB flushing on s390 working again you need
this patch:

--
[PATCH] s390: preemptible mmu_gather

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

Adapt the stand-alone s390 mmu_gather implementation to the new
preemptible mmu_gather interface.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
arch/s390/include/asm/tlb.h | 43 +++++++++++++++++++++++++------------------
1 file changed, 25 insertions(+), 18 deletions(-)

--- a/arch/s390/include/asm/tlb.h
+++ b/arch/s390/include/asm/tlb.h
@@ -28,45 +28,51 @@
#include <asm/smp.h>
#include <asm/tlbflush.h>

-#ifndef CONFIG_SMP
-#define TLB_NR_PTRS 1
-#else
-#define TLB_NR_PTRS 508
-#endif
-
struct mmu_gather {
struct mm_struct *mm;
unsigned int fullmm;
unsigned int nr_ptes;
unsigned int nr_pxds;
- void *array[TLB_NR_PTRS];
+ unsigned int max;
+ void **array;
+ void *local[8];
};

-DECLARE_PER_CPU(struct mmu_gather, mmu_gathers);
-
-static inline struct mmu_gather *tlb_gather_mmu(struct mm_struct *mm,
- unsigned int full_mm_flush)
+static inline void __tlb_alloc_pages(struct mmu_gather *tlb)
{
- struct mmu_gather *tlb = &get_cpu_var(mmu_gathers);
+ unsigned long addr = __get_free_pages(GFP_ATOMIC, 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 || (num_online_cpus() == 1) ||
(atomic_read(&mm->mm_users) <= 1 && mm == current->active_mm);
- tlb->nr_ptes = 0;
- tlb->nr_pxds = TLB_NR_PTRS;
if (tlb->fullmm)
__tlb_flush_mm(mm);
- return tlb;
+ else
+ __tlb_alloc_pages(tlb);
+ tlb->nr_ptes = 0;
+ tlb->nr_pxds = tlb->max;
}

static inline void tlb_flush_mmu(struct mmu_gather *tlb,
unsigned long start, unsigned long end)
{
- if (!tlb->fullmm && (tlb->nr_ptes > 0 || tlb->nr_pxds < TLB_NR_PTRS))
+ if (!tlb->fullmm && (tlb->nr_ptes > 0 || tlb->nr_pxds < tlb->max))
__tlb_flush_mm(tlb->mm);
while (tlb->nr_ptes > 0)
pte_free(tlb->mm, tlb->array[--tlb->nr_ptes]);
- while (tlb->nr_pxds < TLB_NR_PTRS)
+ while (tlb->nr_pxds < tlb->max)
/* pgd_free frees the pointer as region or segment table */
pgd_free(tlb->mm, tlb->array[tlb->nr_pxds++]);
}
@@ -79,7 +85,8 @@ static inline void tlb_finish_mmu(struct
/* keep the page table cache within bounds */
check_pgt_cache();

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

/*

--
blue skies,
Martin.

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