Re: [PATCH] mm: Move __vma_address() to internal.h to be inlined in huge_memory.c

[Waiman Long]

On 06/12/2014 03:25 PM, Andrew Morton wrote:
> On Thu, 12 Jun 2014 15:15:40 -0400 Waiman Long<Waiman.Long@xxxxxx>  wrote:
>
> > The vma_address() function which is used to compute the virtual address
> > within a VMA is used only by 2 files in the mm subsystem - rmap.c and
> > huge_memory.c. This function is defined in rmap.c and is inlined by
> > its callers there, but it is also declared as an external function.
> >
> > However, the __split_huge_page() function which calls vma_address()
> > in huge_memory.c is calling it as a real function call. This is not
> > as efficient as an inlined function. This patch moves the underlying
> > inlined __vma_address() function to internal.h to be shared by both
> > the rmap.c and huge_memory.c file.
> This increases huge_memory.o's text+data_bss by 311 bytes, which makes
> me suspect that it is a bad change due to its increase of kernel cache
> footprint.
>
> Perhaps we should be noinlining __vma_address()?

On my test machine, I saw an increase of 144 bytes in the text segment
of huge_memory.o. The size in size is caused by an increase in the size
of the __split_huge_page function. When I remove the

        if (unlikely(is_vm_hugetlb_page(vma)))
                pgoff = page->index << huge_page_order(page_hstate(page));

check, the increase in size drops down to 24 bytes. As a THP cannot be
a hugetlb page, there is no point in doing this check for a THP. I will
update the patch to pass in an additional argument to disable this
check for __split_huge_page.

-Longman

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