[CRIU] [PATCH 1/6] Replace PAGE_SIZE in vaddr_to_pfn

[Christopher Covington]

On 10/08/2014 08:43 AM, Cyrill Gorcunov wrote:
> On Wed, Oct 08, 2014 at 08:13:36AM -0400, Christopher Covington wrote:
>> On 10/07/2014 05:15 AM, Cyrill Gorcunov wrote:
>>> On Tue, Oct 07, 2014 at 01:06:54PM +0400, Pavel Emelyanov wrote:
>>>> On 10/06/2014 10:50 PM, Christopher Covington wrote:
>>>>> On AArch64, pages may be 4K or 64K depending on kernel configuration.
>>>>> Instead of using the build time constant PAGE_SIZE, query the page
>>>>> size at run time using sysconf(_SC_PAGESIZE).
>>>>
>>>> AFAIK on x86 the PAGE_SIZE is always 4k (Cyrill?).
>>>
>>> yes (on hw level it is not, but from software view PAGE_SIZE is always 4k)
>>>
>>>> If this is true, can we have the vaddr_to_pfn() still operate on
>>>> a constant rather than the _sysconf() call for x86?
>>>
>>> This kind of things should be wrapped with #ifdef depending on
>>> arch we're working on and for x86 it should remains 4k constant.
>>
>> If the difference between this being a libc call and a macro significantly
>> impacts performance then maybe I should explore a templated approach. I'm
>> thinking it should be possible to essentially build the code, or parts of it,
>> once with -D PAGE_SIZE 4096 and again with -D PAGE_SIZE 65536 and then run the
>> appropriate version based on a single initial call to sysconf(). This might
>> also lay the foundation for a single binary, both for ARM and x86, that can
>> dump both 32-bit and 64-bit programs. Would this be worth exploring?
> 
> Yeah, looks good to me. Even more -- in our build engine we can investigate
> the page size and move PAGE_SIZE into config.h (I suppose arm doesn't run
> kernel with different page sizes simultaneously, right?)

For a given kernel the PAGE_SIZE will be constant. However, I'd like for an
AArch64 CRIU built on one kernel (or cross-compiled) to work on as many other
kernels as possible, in particular those with different PAGE_SIZE and TASK_SIZE.

> IOW we can do something (in Makefile.config)
> 
> ifeq ($(ARCH),arm)
> ifeq ($(call try-cc,$(PAGE_SIZE_TEST_65536),),y)
> 	$(Q) @echo '#define CONFIG_PAGE_SIZE 65536' >> $@
> elseif ($(call try-cc,$(PAGE_SIZE_TEST_4096),),y)
> 	$(Q) @echo '#define CONFIG_PAGE_SIZE 4096' >> $@
> endif
> endif

Just to clarify, this only affects 64-bit ARM ("AArch64"), ARCH=aarch64.
32-bit ARM ("AArch32"), ARCH=arm, only has a 4K PAGE_SIZE.

Thanks,
Christopher

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