* [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped:q
@ 2013-05-10 9:01 Zhang Yanfei
2013-05-10 9:27 ` Yinghai Lu
0 siblings, 1 reply; 6+ messages in thread
From: Zhang Yanfei @ 2013-05-10 9:01 UTC (permalink / raw)
To: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, Andrew Morton
Cc: yinghai, linux-kernel
init_memory_mapping will set max_pfn_mapped:
int_memory_mapping
--> add_pfn_range_mapped
--> max_pfn_mapped = max(max_pfn_mapped, end_pfn)
In init_mem_mapping, before we set max_pfn_mapped to 0, we
have already called init_memory_mapping to setup pagetable
for [0, ISA_END_ADDRESS], and that sets max_pfn_mapped. So
the assignment to 0 is not necessary, remove it.
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Yinghai Lu <yinghai@kernel.org>
---
arch/x86/mm/init.c | 1 -
1 files changed, 0 insertions(+), 1 deletions(-)
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index fdc5dca..404c889 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -416,7 +416,6 @@ void __init init_mem_mapping(void)
/* step_size need to be small so pgt_buf from BRK could cover it */
step_size = PMD_SIZE;
- max_pfn_mapped = 0; /* will get exact value next */
min_pfn_mapped = real_end >> PAGE_SHIFT;
last_start = start = real_end;
while (last_start > ISA_END_ADDRESS) {
--
1.7.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped:q
2013-05-10 9:01 [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped:q Zhang Yanfei
@ 2013-05-10 9:27 ` Yinghai Lu
2013-05-10 10:28 ` Zhang Yanfei
0 siblings, 1 reply; 6+ messages in thread
From: Yinghai Lu @ 2013-05-10 9:27 UTC (permalink / raw)
To: Zhang Yanfei
Cc: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, Andrew Morton,
linux-kernel
On Fri, May 10, 2013 at 2:01 AM, Zhang Yanfei
<zhangyanfei@cn.fujitsu.com> wrote:
> init_memory_mapping will set max_pfn_mapped:
> int_memory_mapping
> --> add_pfn_range_mapped
> --> max_pfn_mapped = max(max_pfn_mapped, end_pfn)
>
> In init_mem_mapping, before we set max_pfn_mapped to 0, we
> have already called init_memory_mapping to setup pagetable
> for [0, ISA_END_ADDRESS], and that sets max_pfn_mapped. So
> the assignment to 0 is not necessary, remove it.
NAK.
for 32bit or Xen, max_pfn_mapped is set way before in head_32.S and
xen-enlighen.
Yinghai
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped:q
2013-05-10 9:27 ` Yinghai Lu
@ 2013-05-10 10:28 ` Zhang Yanfei
2013-05-10 14:57 ` Yinghai Lu
0 siblings, 1 reply; 6+ messages in thread
From: Zhang Yanfei @ 2013-05-10 10:28 UTC (permalink / raw)
To: Yinghai Lu
Cc: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, Andrew Morton,
linux-kernel
于 2013年05月10日 17:27, Yinghai Lu 写道:
> On Fri, May 10, 2013 at 2:01 AM, Zhang Yanfei
> <zhangyanfei@cn.fujitsu.com> wrote:
>> init_memory_mapping will set max_pfn_mapped:
>> int_memory_mapping
>> --> add_pfn_range_mapped
>> --> max_pfn_mapped = max(max_pfn_mapped, end_pfn)
>>
>> In init_mem_mapping, before we set max_pfn_mapped to 0, we
>> have already called init_memory_mapping to setup pagetable
>> for [0, ISA_END_ADDRESS], and that sets max_pfn_mapped. So
>> the assignment to 0 is not necessary, remove it.
>
> NAK.
>
> for 32bit or Xen, max_pfn_mapped is set way before in head_32.S and
> xen-enlighen.
Hi Yinghai
I might be wrong, but just from the code in init_mem_mapping only:
410 /* the ISA range is always mapped regardless of memory holes */
411 init_memory_mapping(0, ISA_END_ADDRESS);
412
413 /* xen has big range in reserved near end of ram, skip it at first.*/
414 addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE, PMD_SIZE);
415 real_end = addr + PMD_SIZE;
416
417 /* step_size need to be small so pgt_buf from BRK could cover it */
418 step_size = PMD_SIZE;
419 max_pfn_mapped = 0; /* will get exact value next */
Line 411 set max_pfn_mapped, and then line 419 set it to zero again, so
why keep the later assignment?
Thanks
Zhang
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped:q
2013-05-10 10:28 ` Zhang Yanfei
@ 2013-05-10 14:57 ` Yinghai Lu
2013-05-11 7:36 ` Ingo Molnar
2013-05-15 4:44 ` [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped Zhang Yanfei
0 siblings, 2 replies; 6+ messages in thread
From: Yinghai Lu @ 2013-05-10 14:57 UTC (permalink / raw)
To: Zhang Yanfei
Cc: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, Andrew Morton,
linux-kernel
On Fri, May 10, 2013 at 3:28 AM, Zhang Yanfei
<zhangyanfei@cn.fujitsu.com> wrote:
> 于 2013年05月10日 17:27, Yinghai Lu 写道:
>> On Fri, May 10, 2013 at 2:01 AM, Zhang Yanfei
>> <zhangyanfei@cn.fujitsu.com> wrote:
>>> init_memory_mapping will set max_pfn_mapped:
>>> int_memory_mapping
>>> --> add_pfn_range_mapped
>>> --> max_pfn_mapped = max(max_pfn_mapped, end_pfn)
>>>
>>> In init_mem_mapping, before we set max_pfn_mapped to 0, we
>>> have already called init_memory_mapping to setup pagetable
>>> for [0, ISA_END_ADDRESS], and that sets max_pfn_mapped. So
>>> the assignment to 0 is not necessary, remove it.
>>
>> NAK.
>>
>> for 32bit or Xen, max_pfn_mapped is set way before in head_32.S and
>> xen-enlighen.
>
> Hi Yinghai
>
> I might be wrong, but just from the code in init_mem_mapping only:
>
> 410 /* the ISA range is always mapped regardless of memory holes */
> 411 init_memory_mapping(0, ISA_END_ADDRESS);
> 412
> 413 /* xen has big range in reserved near end of ram, skip it at first.*/
> 414 addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE, PMD_SIZE);
> 415 real_end = addr + PMD_SIZE;
> 416
> 417 /* step_size need to be small so pgt_buf from BRK could cover it */
> 418 step_size = PMD_SIZE;
> 419 max_pfn_mapped = 0; /* will get exact value next */
>
> Line 411 set max_pfn_mapped, and then line 419 set it to zero again, so
> why keep the later assignment?
the comment says: /* will get exact value next */
For x86 32bit path, and xen set bigger max_pfn_mapped before.
Yinghai
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped:q
2013-05-10 14:57 ` Yinghai Lu
@ 2013-05-11 7:36 ` Ingo Molnar
2013-05-15 4:44 ` [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped Zhang Yanfei
1 sibling, 0 replies; 6+ messages in thread
From: Ingo Molnar @ 2013-05-11 7:36 UTC (permalink / raw)
To: Yinghai Lu
Cc: Zhang Yanfei, H. Peter Anvin, Thomas Gleixner, Ingo Molnar,
Andrew Morton, linux-kernel
* Yinghai Lu <yinghai@kernel.org> wrote:
> On Fri, May 10, 2013 at 3:28 AM, Zhang Yanfei
> <zhangyanfei@cn.fujitsu.com> wrote:
> > ?? 2013??05??10?? 17:27, Yinghai Lu ????:
> >> On Fri, May 10, 2013 at 2:01 AM, Zhang Yanfei
> >> <zhangyanfei@cn.fujitsu.com> wrote:
> >>> init_memory_mapping will set max_pfn_mapped:
> >>> int_memory_mapping
> >>> --> add_pfn_range_mapped
> >>> --> max_pfn_mapped = max(max_pfn_mapped, end_pfn)
> >>>
> >>> In init_mem_mapping, before we set max_pfn_mapped to 0, we
> >>> have already called init_memory_mapping to setup pagetable
> >>> for [0, ISA_END_ADDRESS], and that sets max_pfn_mapped. So
> >>> the assignment to 0 is not necessary, remove it.
> >>
> >> NAK.
> >>
> >> for 32bit or Xen, max_pfn_mapped is set way before in head_32.S and
> >> xen-enlighen.
> >
> > Hi Yinghai
> >
> > I might be wrong, but just from the code in init_mem_mapping only:
> >
> > 410 /* the ISA range is always mapped regardless of memory holes */
> > 411 init_memory_mapping(0, ISA_END_ADDRESS);
> > 412
> > 413 /* xen has big range in reserved near end of ram, skip it at first.*/
> > 414 addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE, PMD_SIZE);
> > 415 real_end = addr + PMD_SIZE;
> > 416
> > 417 /* step_size need to be small so pgt_buf from BRK could cover it */
> > 418 step_size = PMD_SIZE;
> > 419 max_pfn_mapped = 0; /* will get exact value next */
> >
> > Line 411 set max_pfn_mapped, and then line 419 set it to zero again, so
> > why keep the later assignment?
>
> the comment says: /* will get exact value next */
And what does that comment mean??
next where? Which call? How? What's the logic? Where is it described
accurately so that people who haven't seen the code (for a while) can
understand it?
> For x86 32bit path, and xen set bigger max_pfn_mapped before.
and what does this mean? Perhaps:
"32-bit x86 and Xen set a bigger value for max_pfn_mapped before this
call."
?
And where and why does it matter that we set a bigger max_pfn_mapped
before?
The dependencies in this code are incestous.
Thanks,
Ingo
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped
2013-05-10 14:57 ` Yinghai Lu
2013-05-11 7:36 ` Ingo Molnar
@ 2013-05-15 4:44 ` Zhang Yanfei
1 sibling, 0 replies; 6+ messages in thread
From: Zhang Yanfei @ 2013-05-15 4:44 UTC (permalink / raw)
To: Yinghai Lu
Cc: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, Andrew Morton,
linux-kernel
于 2013年05月10日 22:57, Yinghai Lu 写道:
> On Fri, May 10, 2013 at 3:28 AM, Zhang Yanfei
> <zhangyanfei@cn.fujitsu.com> wrote:
>> 于 2013年05月10日 17:27, Yinghai Lu 写道:
>>> On Fri, May 10, 2013 at 2:01 AM, Zhang Yanfei
>>> <zhangyanfei@cn.fujitsu.com> wrote:
>>>> init_memory_mapping will set max_pfn_mapped:
>>>> int_memory_mapping
>>>> --> add_pfn_range_mapped
>>>> --> max_pfn_mapped = max(max_pfn_mapped, end_pfn)
>>>>
>>>> In init_mem_mapping, before we set max_pfn_mapped to 0, we
>>>> have already called init_memory_mapping to setup pagetable
>>>> for [0, ISA_END_ADDRESS], and that sets max_pfn_mapped. So
>>>> the assignment to 0 is not necessary, remove it.
>>>
>>> NAK.
>>>
>>> for 32bit or Xen, max_pfn_mapped is set way before in head_32.S and
>>> xen-enlighen.
>>
>> Hi Yinghai
>>
>> I might be wrong, but just from the code in init_mem_mapping only:
>>
>> 410 /* the ISA range is always mapped regardless of memory holes */
>> 411 init_memory_mapping(0, ISA_END_ADDRESS);
>> 412
>> 413 /* xen has big range in reserved near end of ram, skip it at first.*/
>> 414 addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE, PMD_SIZE);
>> 415 real_end = addr + PMD_SIZE;
>> 416
>> 417 /* step_size need to be small so pgt_buf from BRK could cover it */
>> 418 step_size = PMD_SIZE;
>> 419 max_pfn_mapped = 0; /* will get exact value next */
>>
>> Line 411 set max_pfn_mapped, and then line 419 set it to zero again, so
>> why keep the later assignment?
>
> the comment says: /* will get exact value next */
>
> For x86 32bit path, and xen set bigger max_pfn_mapped before.
>
Hello Yinghai,
I kindly understand what you mean now. But I think we can put the reset of
max_pfn_mapped at the beginning of init_mem_mapping. That looks more logical.
See patch below, please.
Thanks
Zhang
------
>From dbd213301d800299d256c5da65a1d598902ed826 Mon Sep 17 00:00:00 2001
From: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Date: Wed, 15 May 2013 11:48:19 +0800
Subject: [PATCH] x86, mm: Reset max_pfn_mapped before we create direct mappings
We use init_mem_mapping to create direct mappings from scratch. But
in 32bit or xen, we may have already set max_pfn_mapped before in
head_32.S and or xen-enlighten. So put the reset at beginning not
in the middle of init_mem_mapping seems more logical.
Also add comments to explain the reset.
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
---
arch/x86/mm/init.c | 9 ++++++++-
1 files changed, 8 insertions(+), 1 deletions(-)
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index fdc5dca..f2e5d28 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -407,6 +407,14 @@ void __init init_mem_mapping(void)
end = max_low_pfn << PAGE_SHIFT;
#endif
+ /*
+ * In 32bit or xen, max_pfn_mapped has been set way before in
+ * head_32.S or xen-enlighten. So here we reset it since we will
+ * create direct mappings from scratch. And it will get its finally
+ * exact value after we finish the direct mapping in this function.
+ */
+ max_pfn_mapped = 0;
+
/* the ISA range is always mapped regardless of memory holes */
init_memory_mapping(0, ISA_END_ADDRESS);
@@ -416,7 +424,6 @@ void __init init_mem_mapping(void)
/* step_size need to be small so pgt_buf from BRK could cover it */
step_size = PMD_SIZE;
- max_pfn_mapped = 0; /* will get exact value next */
min_pfn_mapped = real_end >> PAGE_SHIFT;
last_start = start = real_end;
while (last_start > ISA_END_ADDRESS) {
--
1.7.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
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2013-05-10 9:01 [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped:q Zhang Yanfei
2013-05-10 9:27 ` Yinghai Lu
2013-05-10 10:28 ` Zhang Yanfei
2013-05-10 14:57 ` Yinghai Lu
2013-05-11 7:36 ` Ingo Molnar
2013-05-15 4:44 ` [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped Zhang Yanfei
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