From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f69.google.com (mail-oi0-f69.google.com [209.85.218.69]) by kanga.kvack.org (Postfix) with ESMTP id 5781D6B02AC for ; Wed, 22 Nov 2017 14:30:52 -0500 (EST) Received: by mail-oi0-f69.google.com with SMTP id r190so7970469oie.14 for ; Wed, 22 Nov 2017 11:30:52 -0800 (PST) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id v74si6437991oia.545.2017.11.22.11.30.51 for ; Wed, 22 Nov 2017 11:30:51 -0800 (PST) Date: Wed, 22 Nov 2017 19:30:50 +0000 From: Will Deacon Subject: Re: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy Message-ID: <20171122193049.GI22648@arm.com> References: <20171107095453.179940-1-wangnan0@huawei.com> <20171110001933.GA12421@bbox> <20171110101529.op6yaxtdke2p4bsh@dhcp22.suse.cz> <20171110122635.q26xdxytgdfjy5q3@dhcp22.suse.cz> <20171115173332.GL19071@arm.com> <20171116092042.esxqtnfxdrozfwey@dhcp22.suse.cz> <20171120142444.GA32488@arm.com> <20171120160422.5ieustt5ovbyelyx@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171120160422.5ieustt5ovbyelyx@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Minchan Kim , Wang Nan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Bob Liu , Andrew Morton , David Rientjes , Ingo Molnar , Roman Gushchin , Konstantin Khlebnikov , Andrea Arcangeli Hi Michal, On Mon, Nov 20, 2017 at 05:04:22PM +0100, Michal Hocko wrote: > On Mon 20-11-17 14:24:44, Will Deacon wrote: > > On Thu, Nov 16, 2017 at 10:20:42AM +0100, Michal Hocko wrote: > > > On Wed 15-11-17 17:33:32, Will Deacon wrote: > [...] > > > > > diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h > > > > > index ffdaea7954bb..7adde19b2bcc 100644 > > > > > --- a/arch/arm64/include/asm/tlb.h > > > > > +++ b/arch/arm64/include/asm/tlb.h > > > > > @@ -43,7 +43,7 @@ static inline void tlb_flush(struct mmu_gather *tlb) > > > > > * The ASID allocator will either invalidate the ASID or mark > > > > > * it as used. > > > > > */ > > > > > - if (tlb->fullmm) > > > > > + if (tlb->lazy) > > > > > return; > > > > > > > > This looks like the right idea, but I'd rather make this check: > > > > > > > > if (tlb->fullmm && tlb->lazy) > > > > > > > > since the optimisation doesn't work for anything than tearing down the > > > > entire address space. > > > > > > OK, that makes sense. > > > > > > > Alternatively, I could actually go check MMF_UNSTABLE in tlb->mm, which > > > > would save you having to add an extra flag in the first place, e.g.: > > > > > > > > if (tlb->fullmm && !test_bit(MMF_UNSTABLE, &tlb->mm->flags)) > > > > > > > > which is a nice one-liner. > > > > > > But that would make it oom_reaper specific. What about the softdirty > > > case Minchan has mentioned earlier? > > > > We don't (yet) support that on arm64, so we're ok for now. If we do grow > > support for it, then I agree that we want a flag to identify the case where > > the address space is going away and only elide the invalidation then. > > What do you think about the following patch instead? I have to confess > I do not really understand the fullmm semantic so I might introduce some > duplication by this flag. If you think this is a good idea, I will post > it in a separate thread. Please do! My only suggestion would be s/lazy/exit/, since I don't think the optimisation works in any other situation than the address space going away for good. Will -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org