linux-kernel - Re: [RFC PATCH 1/2] mm/mmu_gather: Invalidate TLB correctly on batch allocation failure and flush

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Message-ID: <20191217123544.GI2827@hirez.programming.kicks-ass.net>
Date:   Tue, 17 Dec 2019 13:35:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     akpm@...ux-foundation.org, npiggin@...il.com, mpe@...erman.id.au,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH 1/2] mm/mmu_gather: Invalidate TLB correctly on batch
 allocation failure and flush

On Tue, Dec 17, 2019 at 04:18:40PM +0530, Aneesh Kumar K.V wrote:
> On 12/17/19 2:39 PM, Peter Zijlstra wrote:
> > On Tue, Dec 17, 2019 at 12:47:12PM +0530, Aneesh Kumar K.V wrote:
> > > Architectures for which we have hardware walkers of Linux page table should
> > > flush TLB on mmu gather batch allocation failures and batch flush. Some
> > > architectures like POWER supports multiple translation modes (hash and radix)
> > > and in the case of POWER only radix translation mode needs the above TLBI.
> > > This is because for hash translation mode kernel wants to avoid this extra
> > > flush since there are no hardware walkers of linux page table. With radix
> > > translation, the hardware also walks linux page table and with that, kernel
> > > needs to make sure to TLB invalidate page walk cache before page table pages are
> > > freed.
> > 
> > > Based on changes from Peter Zijlstra <peterz@...radead.org>
> > 
> > AFAICT it is all my patch ;-)
> 
> Yes. I moved the changes you had to upstream. I can update the From: in the
> next version if you are ok with that?

Well, since PPC isn't broken per finding the invalidate in
__p*_free_tlb(), lets do these things on top of the patches I proposed
here. Also, you mnight want to run benchmarks to see if the movement of
that TLBI actually helps (I'm thinking the cost of the PTESYNC might add
up).