Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Laurent Dufour]

On 17/05/2018 18:36, Randy Dunlap wrote:
> Hi,
> 
> On 05/17/2018 04:06 AM, Laurent Dufour wrote:
>> This configuration variable will be used to build the code needed to
>> handle speculative page fault.
>>
>> By default it is turned off, and activated depending on architecture
>> support, ARCH_HAS_PTE_SPECIAL, SMP and MMU.
>>
>> The architecture support is needed since the speculative page fault handler
>> is called from the architecture's page faulting code, and some code has to
>> be added there to handle the speculative handler.
>>
>> The dependency on ARCH_HAS_PTE_SPECIAL is required because vm_normal_page()
>> does processing that is not compatible with the speculative handling in the
>> case ARCH_HAS_PTE_SPECIAL is not set.
>>
>> Suggested-by: Thomas Gleixner 
>> Suggested-by: David Rientjes 
>> Signed-off-by: Laurent Dufour 
>> ---
>>  mm/Kconfig | 22 ++
>>  1 file changed, 22 insertions(+)
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 1d0888c5b97a..a38796276113 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -761,3 +761,25 @@ config GUP_BENCHMARK
>>  
>>  config ARCH_HAS_PTE_SPECIAL
>>  bool
>> +
>> +config ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>> +   def_bool n
>> +
>> +config SPECULATIVE_PAGE_FAULT
>> +   bool "Speculative page faults"
>> +   default y
>> +   depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>> +   depends on ARCH_HAS_PTE_SPECIAL && MMU && SMP
>> +   help
>> + Try to handle user space page faults without holding the mmap_sem.
>> +
>> + This should allow better concurrency for massively threaded process
> 
>processes
> 
>> + since the page fault handler will not wait for other threads memory
> 
> thread's
> 
>> + layout change to be done, assuming that this change is done in another
>> + part of the process's memory space. This type of page fault is named
>> + speculative page fault.
>> +
>> + If the speculative page fault fails because of a concurrency is
> 
>because a concurrency is
> 
>> + detected or because underlying PMD or PTE tables are not yet
>> + allocating, it is failing its processing and a classic page fault
> 
>allocated, the speculative page fault fails and a classic page fault
> 
>> + is then tried.
> 
> 
> Also, all of the help text (below the "help" line) should be indented by
> 1 tab + 2 spaces (in coding-style.rst).

Thanks, Randy for reviewing my miserable English grammar.
I'll fix that and the indentation.

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Laurent Dufour]

On 17/05/2018 18:36, Randy Dunlap wrote:
> Hi,
> 
> On 05/17/2018 04:06 AM, Laurent Dufour wrote:
>> This configuration variable will be used to build the code needed to
>> handle speculative page fault.
>>
>> By default it is turned off, and activated depending on architecture
>> support, ARCH_HAS_PTE_SPECIAL, SMP and MMU.
>>
>> The architecture support is needed since the speculative page fault handler
>> is called from the architecture's page faulting code, and some code has to
>> be added there to handle the speculative handler.
>>
>> The dependency on ARCH_HAS_PTE_SPECIAL is required because vm_normal_page()
>> does processing that is not compatible with the speculative handling in the
>> case ARCH_HAS_PTE_SPECIAL is not set.
>>
>> Suggested-by: Thomas Gleixner 
>> Suggested-by: David Rientjes 
>> Signed-off-by: Laurent Dufour 
>> ---
>>  mm/Kconfig | 22 ++
>>  1 file changed, 22 insertions(+)
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 1d0888c5b97a..a38796276113 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -761,3 +761,25 @@ config GUP_BENCHMARK
>>  
>>  config ARCH_HAS_PTE_SPECIAL
>>  bool
>> +
>> +config ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>> +   def_bool n
>> +
>> +config SPECULATIVE_PAGE_FAULT
>> +   bool "Speculative page faults"
>> +   default y
>> +   depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>> +   depends on ARCH_HAS_PTE_SPECIAL && MMU && SMP
>> +   help
>> + Try to handle user space page faults without holding the mmap_sem.
>> +
>> + This should allow better concurrency for massively threaded process
> 
>processes
> 
>> + since the page fault handler will not wait for other threads memory
> 
> thread's
> 
>> + layout change to be done, assuming that this change is done in another
>> + part of the process's memory space. This type of page fault is named
>> + speculative page fault.
>> +
>> + If the speculative page fault fails because of a concurrency is
> 
>because a concurrency is
> 
>> + detected or because underlying PMD or PTE tables are not yet
>> + allocating, it is failing its processing and a classic page fault
> 
>allocated, the speculative page fault fails and a classic page fault
> 
>> + is then tried.
> 
> 
> Also, all of the help text (below the "help" line) should be indented by
> 1 tab + 2 spaces (in coding-style.rst).

Thanks, Randy for reviewing my miserable English grammar.
I'll fix that and the indentation.

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Laurent Dufour]

On 17/05/2018 19:19, Matthew Wilcox wrote:
> On Thu, May 17, 2018 at 09:36:00AM -0700, Randy Dunlap wrote:
>>> +If the speculative page fault fails because of a concurrency is
>>
>>   because a concurrency is
> 
> While one can use concurrency as a noun, it sounds archaic to me.  I'd
> rather:
> 
>   If the speculative page fault fails because a concurrent modification
>   is detected or because underlying PMD or PTE tables are not yet

Thanks Matthew, I'll do that.

> 
>>> +detected or because underlying PMD or PTE tables are not yet
>>> +allocating, it is failing its processing and a classic page fault
>>
>>   allocated, the speculative page fault fails and a classic page fault
>>
>>> +is then tried.
> 

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Laurent Dufour]

On 17/05/2018 19:19, Matthew Wilcox wrote:
> On Thu, May 17, 2018 at 09:36:00AM -0700, Randy Dunlap wrote:
>>> +If the speculative page fault fails because of a concurrency is
>>
>>   because a concurrency is
> 
> While one can use concurrency as a noun, it sounds archaic to me.  I'd
> rather:
> 
>   If the speculative page fault fails because a concurrent modification
>   is detected or because underlying PMD or PTE tables are not yet

Thanks Matthew, I'll do that.

> 
>>> +detected or because underlying PMD or PTE tables are not yet
>>> +allocating, it is failing its processing and a classic page fault
>>
>>   allocated, the speculative page fault fails and a classic page fault
>>
>>> +is then tried.
> 

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Randy Dunlap]

On 05/17/2018 10:19 AM, Matthew Wilcox wrote:
> On Thu, May 17, 2018 at 09:36:00AM -0700, Randy Dunlap wrote:
>>> +If the speculative page fault fails because of a concurrency is
>>
>>   because a concurrency is
> 
> While one can use concurrency as a noun, it sounds archaic to me.  I'd
> rather:
> 
>   If the speculative page fault fails because a concurrent modification
>   is detected or because underlying PMD or PTE tables are not yet

Yeah, OK.

>>> +detected or because underlying PMD or PTE tables are not yet
>>> +allocating, it is failing its processing and a classic page fault
>>
>>   allocated, the speculative page fault fails and a classic page fault
>>
>>> +is then tried.


-- 
~Randy

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Randy Dunlap]

On 05/17/2018 10:19 AM, Matthew Wilcox wrote:
> On Thu, May 17, 2018 at 09:36:00AM -0700, Randy Dunlap wrote:
>>> +If the speculative page fault fails because of a concurrency is
>>
>>   because a concurrency is
> 
> While one can use concurrency as a noun, it sounds archaic to me.  I'd
> rather:
> 
>   If the speculative page fault fails because a concurrent modification
>   is detected or because underlying PMD or PTE tables are not yet

Yeah, OK.

>>> +detected or because underlying PMD or PTE tables are not yet
>>> +allocating, it is failing its processing and a classic page fault
>>
>>   allocated, the speculative page fault fails and a classic page fault
>>
>>> +is then tried.


-- 
~Randy

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Matthew Wilcox]

On Thu, May 17, 2018 at 09:36:00AM -0700, Randy Dunlap wrote:
> > +If the speculative page fault fails because of a concurrency is
> 
>because a concurrency is

While one can use concurrency as a noun, it sounds archaic to me.  I'd
rather:

If the speculative page fault fails because a concurrent modification
is detected or because underlying PMD or PTE tables are not yet

> > +detected or because underlying PMD or PTE tables are not yet
> > +allocating, it is failing its processing and a classic page fault
> 
>allocated, the speculative page fault fails and a classic page fault
> 
> > +is then tried.

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Matthew Wilcox]

On Thu, May 17, 2018 at 09:36:00AM -0700, Randy Dunlap wrote:
> > +If the speculative page fault fails because of a concurrency is
> 
>because a concurrency is

While one can use concurrency as a noun, it sounds archaic to me.  I'd
rather:

If the speculative page fault fails because a concurrent modification
is detected or because underlying PMD or PTE tables are not yet

> > +detected or because underlying PMD or PTE tables are not yet
> > +allocating, it is failing its processing and a classic page fault
> 
>allocated, the speculative page fault fails and a classic page fault
> 
> > +is then tried.

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Randy Dunlap]

Hi,

On 05/17/2018 04:06 AM, Laurent Dufour wrote:
> This configuration variable will be used to build the code needed to
> handle speculative page fault.
> 
> By default it is turned off, and activated depending on architecture
> support, ARCH_HAS_PTE_SPECIAL, SMP and MMU.
> 
> The architecture support is needed since the speculative page fault handler
> is called from the architecture's page faulting code, and some code has to
> be added there to handle the speculative handler.
> 
> The dependency on ARCH_HAS_PTE_SPECIAL is required because vm_normal_page()
> does processing that is not compatible with the speculative handling in the
> case ARCH_HAS_PTE_SPECIAL is not set.
> 
> Suggested-by: Thomas Gleixner 
> Suggested-by: David Rientjes 
> Signed-off-by: Laurent Dufour 
> ---
>  mm/Kconfig | 22 ++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 1d0888c5b97a..a38796276113 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -761,3 +761,25 @@ config GUP_BENCHMARK
>  
>  config ARCH_HAS_PTE_SPECIAL
>   bool
> +
> +config ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> +   def_bool n
> +
> +config SPECULATIVE_PAGE_FAULT
> +   bool "Speculative page faults"
> +   default y
> +   depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> +   depends on ARCH_HAS_PTE_SPECIAL && MMU && SMP
> +   help
> + Try to handle user space page faults without holding the mmap_sem.
> +
> +  This should allow better concurrency for massively threaded process

 processes

> +  since the page fault handler will not wait for other threads memory

  thread's

> +  layout change to be done, assuming that this change is done in another
> +  part of the process's memory space. This type of page fault is named
> +  speculative page fault.
> +
> +  If the speculative page fault fails because of a concurrency is

 because a concurrency is

> +  detected or because underlying PMD or PTE tables are not yet
> +  allocating, it is failing its processing and a classic page fault

 allocated, the speculative page fault fails and a classic page fault

> +  is then tried.


Also, all of the help text (below the "help" line) should be indented by
1 tab + 2 spaces (in coding-style.rst).


-- 
~Randy

Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

[Randy Dunlap]

Hi,

On 05/17/2018 04:06 AM, Laurent Dufour wrote:
> This configuration variable will be used to build the code needed to
> handle speculative page fault.
> 
> By default it is turned off, and activated depending on architecture
> support, ARCH_HAS_PTE_SPECIAL, SMP and MMU.
> 
> The architecture support is needed since the speculative page fault handler
> is called from the architecture's page faulting code, and some code has to
> be added there to handle the speculative handler.
> 
> The dependency on ARCH_HAS_PTE_SPECIAL is required because vm_normal_page()
> does processing that is not compatible with the speculative handling in the
> case ARCH_HAS_PTE_SPECIAL is not set.
> 
> Suggested-by: Thomas Gleixner 
> Suggested-by: David Rientjes 
> Signed-off-by: Laurent Dufour 
> ---
>  mm/Kconfig | 22 ++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 1d0888c5b97a..a38796276113 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -761,3 +761,25 @@ config GUP_BENCHMARK
>  
>  config ARCH_HAS_PTE_SPECIAL
>   bool
> +
> +config ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> +   def_bool n
> +
> +config SPECULATIVE_PAGE_FAULT
> +   bool "Speculative page faults"
> +   default y
> +   depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> +   depends on ARCH_HAS_PTE_SPECIAL && MMU && SMP
> +   help
> + Try to handle user space page faults without holding the mmap_sem.
> +
> +  This should allow better concurrency for massively threaded process

 processes

> +  since the page fault handler will not wait for other threads memory

  thread's

> +  layout change to be done, assuming that this change is done in another
> +  part of the process's memory space. This type of page fault is named
> +  speculative page fault.
> +
> +  If the speculative page fault fails because of a concurrency is

 because a concurrency is

> +  detected or because underlying PMD or PTE tables are not yet
> +  allocating, it is failing its processing and a classic page fault

 allocated, the speculative page fault fails and a classic page fault

> +  is then tried.


Also, all of the help text (below the "help" line) should be indented by
1 tab + 2 spaces (in coding-style.rst).


-- 
~Randy