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SubjectRe: [PATCH] mm: eliminate function call overhead during copy_page_range()
On Sun, Feb 05, 2023 at 09:53:53PM +0000, Matthew Wilcox wrote:
> On Sun, Feb 05, 2023 at 03:06:02PM +0000, Hao Lee wrote:
> > vm_normal_page() is called so many times that its overhead is very high.
> > After changing this call site to an inline function, copy_page_range()
> > runs 3~5 times faster than before.
>
> So you're saying that your compiler is making bad decisions? What
> architecture, what compiler, what version? Do you have
> CONFIG_ARCH_HAS_PTE_SPECIAL set?
>
> Is there something about inlining it that makes the compiler able to
> optimise away code, or is it really the function call overhead? Can
> you share any perf results?

I am so embarrassed; I forgot to disable function_graph when timing the
non-inlined function so my test was interfered. And the actual
performance improvement is only ~3%.
Please ignore this patch. Sorry...

>

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