linux-kernel - Re: [PATCH mk-II 08/17] asm-generic/tlb: Provide MMU_GATHER_TABLE

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Message-ID: <20200127081134.GI14914@hirez.programming.kicks-ass.net>
Date:   Mon, 27 Jan 2020 09:11:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Will Deacon <will@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        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 mk-II 08/17] asm-generic/tlb: Provide
 MMU_GATHER_TABLE_FREE

On Sun, Jan 26, 2020 at 07:52:05AM -0800, Guenter Roeck wrote:
> On Thu, Dec 12, 2019 at 10:32:05AM +0100, Peter Zijlstra wrote:
> > As described in the comment, the correct order for freeing pages is:
> > 
> >  1) unhook page
> >  2) TLB invalidate page
> >  3) free page
> > 
> > This order equally applies to page directories.
> > 
> > Currently there are two correct options:
> > 
> >  - use tlb_remove_page(), when all page directores are full pages and
> >    there are no futher contraints placed by things like software
> >    walkers (HAVE_FAST_GUP).
> > 
> >  - use MMU_GATHER_RCU_TABLE_FREE and tlb_remove_table() when the
> >    architecture does not do IPI based TLB invalidate and has
> >    HAVE_FAST_GUP (or software TLB fill).
> > 
> > This however leaves architectures that don't have page based
> > directories but don't need RCU in a bind. For those, provide
> > MMU_GATHER_TABLE_FREE, which provides the independent batching for
> > directories without the additional RCU freeing.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > ---
> 
> Various sparc64 builds (allnoconfig, tinyconfig, as well as builds
> with SMP disabled):
> 
> mm/mmu_gather.c: In function '__tlb_remove_table_free':
> mm/mmu_gather.c:101:3: error: implicit declaration of function '__tlb_remove_table'; did you mean 'tlb_remove_table'?

Thanks; I'll respin these patches against Aneesh' pile and make sure to
look into this when I do so.