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

[Cyrill Gorcunov]

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?)

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

or something like that.