Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 24 Aug 2018 13:32:14 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Will Deacon <will.deacon@arm.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Benjamin Herrenschmidt <benh@au1.ibm.com>,
        Nick Piggin <npiggin@gmail.com>,
        Andrew Lutomirski <luto@kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Rik van Riel <riel@surriel.com>,
        Jann Horn <jannh@google.com>,
        Adin Scannell <ascannell@google.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        David Miller <davem@davemloft.net>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for
 RCU_TABLE_FREE
Message-ID: <20180824113214.GK24142@hirez.programming.kicks-ass.net>
References: <20180822153012.173508681@infradead.org>
 <20180822154046.823850812@infradead.org>
 <20180822155527.GF24124@hirez.programming.kicks-ass.net>
 <20180823134525.5f12b0d3@roar.ozlabs.ibm.com>
 <CA+55aFxneZTFxxxAjLZmj92VUJg6z7hERxJ2cHoth-GC0RuELw@mail.gmail.com>
 <776104d4c8e4fc680004d69e3a4c2594b638b6d1.camel@au1.ibm.com>
 <CA+55aFzM77G9-Q6LboPLJ=5gHma66ZQKiMGCMqXoKABirdF98w@mail.gmail.com>
 <20180823133958.GA1496@brain-police>
 <20180824084717.GK24124@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180824084717.GK24124@hirez.programming.kicks-ass.net>
User-Agent: Mutt/1.10.0 (2018-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Aug 24, 2018 at 10:47:17AM +0200, Peter Zijlstra wrote:
> On Thu, Aug 23, 2018 at 02:39:59PM +0100, Will Deacon wrote:
> > The only problem with this approach is that we've lost track of the granule
> > size by the point we get to the tlb_flush(), so we can't adjust the stride of
> > the TLB invalidations for huge mappings, which actually works nicely in the
> > synchronous case (e.g. we perform a single invalidation for a 2MB mapping,
> > rather than iterating over it at a 4k granule).
> > 
> > One thing we could do is switch to synchronous mode if we detect a change in
> > granule (i.e. treat it like a batch failure).
> 
> We could use tlb_start_vma() to track that, I think. Shouldn't be too
> hard.

Hurm.. look at commit:

  e77b0852b551 ("mm/mmu_gather: track page size with mmu gather and force flush if page size change")

yuck yuck yuck. That needs fixing.