From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot1-f70.google.com (mail-ot1-f70.google.com [209.85.210.70]) by kanga.kvack.org (Postfix) with ESMTP id A14AC8E0001 for ; Wed, 19 Sep 2018 08:23:12 -0400 (EDT) Received: by mail-ot1-f70.google.com with SMTP id e38-v6so4762782otj.15 for ; Wed, 19 Sep 2018 05:23:12 -0700 (PDT) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id k70-v6si7504705otk.129.2018.09.19.05.23.10 for ; Wed, 19 Sep 2018 05:23:11 -0700 (PDT) Date: Wed, 19 Sep 2018 13:23:29 +0100 From: Will Deacon Subject: Re: [RFC][PATCH 01/11] asm-generic/tlb: Provide a comment Message-ID: <20180919122328.GB22723@arm.com> References: <20180913092110.817204997@infradead.org> <20180913092811.894806629@infradead.org> <20180914164857.GG6236@arm.com> <20180919115158.GD24124@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180919115158.GD24124@hirez.programming.kicks-ass.net> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: aneesh.kumar@linux.vnet.ibm.com, akpm@linux-foundation.org, npiggin@gmail.com, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux@armlinux.org.uk, heiko.carstens@de.ibm.com On Wed, Sep 19, 2018 at 01:51:58PM +0200, Peter Zijlstra wrote: > On Fri, Sep 14, 2018 at 05:48:57PM +0100, Will Deacon wrote: > > > > + * - mmu_gather::fullmm > > > + * > > > + * A flag set by tlb_gather_mmu() to indicate we're going to free > > > + * the entire mm; this allows a number of optimizations. > > > + * > > > + * XXX list optimizations > > > > On arm64, we can elide the invalidation altogether because we won't > > re-allocate the ASID. We also have an invalidate-by-ASID (mm) instruction, > > which we could use if we needed to. > > Right, but I was also struggling to put into words the normal fullmm > case. > > I now ended up with: > > --- a/include/asm-generic/tlb.h > +++ b/include/asm-generic/tlb.h > @@ -82,7 +82,11 @@ > * A flag set by tlb_gather_mmu() to indicate we're going to free > * the entire mm; this allows a number of optimizations. > * > - * XXX list optimizations > + * - We can ignore tlb_{start,end}_vma(); because we don't > + * care about ranges. Everything will be shot down. > + * > + * - (RISC) architectures that use ASIDs can cycle to a new ASID > + * and delay the invalidation until ASID space runs out. > * > * - mmu_gather::need_flush_all > * > > Does that about cover things; or do we need more? I think that's fine as a starting point. People can always add more. > > > + * > > > + * - mmu_gather::need_flush_all > > > + * > > > + * A flag that can be set by the arch code if it wants to force > > > + * flush the entire TLB irrespective of the range. For instance > > > + * x86-PAE needs this when changing top-level entries. > > > + * > > > + * And requires the architecture to provide and implement tlb_flush(). > > > + * > > > + * tlb_flush() may, in addition to the above mentioned mmu_gather fields, make > > > + * use of: > > > + * > > > + * - mmu_gather::start / mmu_gather::end > > > + * > > > + * which (when !need_flush_all; fullmm will have start = end = ~0UL) provides > > > + * the range that needs to be flushed to cover the pages to be freed. > > > > I don't understand the mention of need_flush_all here -- I didn't think it > > was used by the core code at all. > > The core does indeed not use that flag; but if the architecture set > that, the range is still ignored. > > Can you suggest clearer wording? The range is only ignored if the default tlb_flush() implementation is used though, right? Since this text is about the fields that tlb_flush() can use, I think we can just delete the part in brackets. Will