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[59.102.83.192]) by smtp.gmail.com with ESMTPSA id 6-v6sm21259619pfr.115.2018.08.27.01.05.01 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 27 Aug 2018 01:05:06 -0700 (PDT) Date: Mon, 27 Aug 2018 18:04:58 +1000 From: Nicholas Piggin To: Peter Zijlstra Cc: Will Deacon , Linus Torvalds , Benjamin Herrenschmidt , Andrew Lutomirski , the arch/x86 maintainers , Borislav Petkov , Rik van Riel , Jann Horn , Adin Scannell , Dave Hansen , Linux Kernel Mailing List , linux-mm , David Miller , Martin Schwidefsky , Michael Ellerman Subject: Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE Message-ID: <20180827180458.4af9b2ac@roar.ozlabs.ibm.com> In-Reply-To: <20180827074701.GW24124@hirez.programming.kicks-ass.net> References: <20180822155527.GF24124@hirez.programming.kicks-ass.net> <20180823134525.5f12b0d3@roar.ozlabs.ibm.com> <776104d4c8e4fc680004d69e3a4c2594b638b6d1.camel@au1.ibm.com> <20180823133958.GA1496@brain-police> <20180824084717.GK24124@hirez.programming.kicks-ass.net> <20180824113214.GK24142@hirez.programming.kicks-ass.net> <20180824113953.GL24142@hirez.programming.kicks-ass.net> <20180827150008.13bce08f@roar.ozlabs.ibm.com> <20180827074701.GW24124@hirez.programming.kicks-ass.net> X-Mailer: Claws Mail 3.17.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 27 Aug 2018 09:47:01 +0200 Peter Zijlstra wrote: > On Mon, Aug 27, 2018 at 03:00:08PM +1000, Nicholas Piggin wrote: > > On Fri, 24 Aug 2018 13:39:53 +0200 > > Peter Zijlstra wrote: > > > On Fri, Aug 24, 2018 at 01:32:14PM +0200, Peter Zijlstra wrote: > > > > > Hurm.. look at commit: > > > > > > > > e77b0852b551 ("mm/mmu_gather: track page size with mmu gather and force flush if page size change") > > > > > > Ah, good, it seems that already got cleaned up a lot. But it all moved > > > into the power code.. blergh. > > > > I lost track of what the problem is here? > > Aside from the commit above being absolute crap (which did get fixed up, > luckily) I would really like to get rid of all arch specific mmu_gather. > > We can have opt-in bits to the generic code, but the endless back and > forth between common and arch code is an utter pain in the arse. > > And there's only like 4 architectures that still have a custom > mmu_gather: > > - sh > - arm > - ia64 > - s390 > > sh is trivial, arm seems doable, with a bit of luck we can do 'rm -rf > arch/ia64' leaving us with s390. Well I don't see a big problem in having an arch_mmu_gather field or small bits. powerpc would actually like that rather than trying to add things it wants into generic code (and it wants more than just a few flags bits, ideally). > After that everyone uses the common code and we can clean up. > > > For powerpc, tlb_start_vma is not the right API to use for this because > > it wants to deal with different page sizes within a vma. > > Yes.. I see that. tlb_remove_check_page_size_change() really is a rather > ugly thing, it can cause loads of TLB flushes. Do you really _have_ to > do that? The way ARM and x86 work is that using INVLPG in a 4K stride is > still correct for huge pages, inefficient maybe, but so is flushing > every other page because 'sparse' transparant-huge-pages. It could do that. It requires a tlbie that matches the page size, so it means 3 sizes. I think possibly even that would be better than current code, but we could do better if we had a few specific fields in there. Thanks, Nick