Re: [PATCH RFC v2 2/2] mm: Rework swap handling of zap_pte_range

From: Peter Xu
Date: Tue Nov 16 2021 - 00:07:09 EST

On Mon, Nov 15, 2021 at 01:57:32PM +0000, Matthew Wilcox wrote:
> On Mon, Nov 15, 2021 at 09:49:51PM +0800, Peter Xu wrote:
> > Clean the code up by merging the device private/exclusive swap entry handling
> > with the rest, then we merge the pte clear operation too.
> >
> > struct* page is defined in multiple places in the function, move it upward.
> Is that actually a good thing? There was a time when declaring
> variables more locally helped compilers with liveness analysis and
> register allocation. Compilers are probably smarter now.

I see, I don't know the history of that, but I did give it a shot with a patch
that recovered all the "struct page*" back to the origin, I found that it'll
generated exactly the same assembly of unmap_page_range (actually, the whole
mm/memory.o) no matter what.

I only tested on an aarch64 system, with below gcc version:

$ gcc -v
Using built-in specs.
Target: aarch64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl= --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl=/builddir/build/BUILD/gcc-11.0.1-20210324/obj-aarch64-redhat-linux/isl-install --enable-gnu-indirect-function --build=aarch64-redhat-linux
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.0.1 20210324 (Red Hat 11.0.1-0) (GCC)


Peter Xu