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References: <20180612071621.26775-1-npiggin@gmail.com> <20180612071621.26775-4-npiggin@gmail.com>
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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Tue, 12 Jun 2018 11:18:27 -0700
Message-ID: <CA+55aFzKBieD0Y3sgFQzt+x5esqb9vT6SEQ28xyCz5UWegfFVg@mail.gmail.com>
Subject: Re: [RFC PATCH 3/3] powerpc/64s/radix: optimise TLB flush with
 precise TLB ranges in mmu_gather
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Sender: owner-linux-mm@kvack.org
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To: Nick Piggin <npiggin@gmail.com>
Cc: linux-mm <linux-mm@kvack.org>, ppc-dev <linuxppc-dev@lists.ozlabs.org>, linux-arch <linux-arch@vger.kernel.org>, "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>, Minchan Kim <minchan@kernel.org>, Mel Gorman <mgorman@techsingularity.net>, Nadav Amit <nadav.amit@gmail.com>, Andrew Morton <akpm@linux-foundation.org>

On Tue, Jun 12, 2018 at 12:16 AM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> This brings the number of tlbiel instructions required by a kernel
> compile from 33M to 25M, most avoided from exec->shift_arg_pages.

And this shows that "page_start/end" is purely for powerpc and used
nowhere else.

The previous patch should have been to purely powerpc page table
walking and not touch asm-generic/tlb.h

I think you should make those changes to
arch/powerpc/include/asm/tlb.h. If that means you can't use the
generic header, then so be it.

Or maybe you can embed the generic case in some ppc-specific
structures, and use 90% of the generic code just with your added
wrappers for that radix invalidation on top.

But don't make other architectures do pointless work that doesn't
matter - or make sense - for them.

               Linus