linux-kernel - Re: [PATCH 05/17] asm-generic/tlb: Rename HAVE_RCU_TABLE_NO

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Message-ID: <33ed03aa-a34c-3a81-0f83-20c3e8d4eff7@linux.ibm.com>
Date:   Mon, 16 Dec 2019 19:24:24 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Helge Deller <deller@....de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Burton <paulburton@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Richard Henderson <rth@...ddle.net>,
        Nick Hu <nickhu@...estech.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH 05/17] asm-generic/tlb: Rename
 HAVE_RCU_TABLE_NO_INVALIDATE

On 12/16/19 7:10 PM, Aneesh Kumar K.V wrote:
> On 12/16/19 6:50 PM, Peter Zijlstra wrote:
>> On Mon, Dec 16, 2019 at 06:43:53PM +0530, Aneesh Kumar K.V wrote:
>>> On 12/16/19 6:07 PM, Peter Zijlstra wrote:
>>
>>>> I'm confused, are you saing you're happy to have PowerPC eat the extra
>>>> TLB invalidates? I thought you cared about PPC performance :-)
>>>>
>>>>
>>>
>>> Instead can we do
>>>
>>> static inline void tlb_table_invalidate(struct mmu_gather *tlb)
>>> {
>>> #ifndef CONFIG_MMU_GATHER_RCU_TABLE_FREE
>>>      * Invalidate page-table caches used by hardware walkers. Then we 
>>> still
>>>      * need to RCU-sched wait while freeing the pages because software
>>>      * walkers can still be in-flight.
>>>      */
>>>     tlb_flush_mmu_tlbonly(tlb);
>>> #endif
>>> }
>>
>> How does that not break ARM/ARM64/s390 and x86 ?
>>
> 
> Hmm I missed that usage of RCU_TABLE_NO_INVALIDATE.
> 
> Ok I guess we need to revert this change that went upstream this merge 
> window then
> 
> commit 52162ec784fa05f3a4b1d8e84421279998be3773
> Author: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Date:   Thu Oct 24 13:28:00 2019 +0530
> 
>      powerpc/mm/book3s64/radix: Use freed_tables instead of need_flush_all
> 
> 
> 
> I will review the change closely.


So __p*_free_tlb() routines on ppc64 just mark that we need a page walk 
cache flush and the actual flush in done in tlb_flush_mmu. As per

d86564a2f085b79ec046a5cba90188e61235280 (mm/tlb, x86/mm: Support 
invalidating TLB caches for RCU_TABLE_FREE ) that is not sufficient?

-aneesh