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Date: Sat, 27 Oct 2018 21:21:02 +1100
From: Balbir Singh <bsingharora@gmail.com>
Subject: Re: [PATCH 2/4] mm: speed up mremap by 500x on large regions (v2)
Message-ID: <20181027102102.GO8537@350D>
References: <20181013013200.206928-1-joel@joelfernandes.org>
 <20181013013200.206928-3-joel@joelfernandes.org>
 <20181024101255.it4lptrjogalxbey@kshutemo-mobl1>
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To: Joel Fernandes <joel@joelfernandes.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>, linux-kernel@vger.kernel.org, kernel-team@android.com, minchan@kernel.org, pantin@google.com, hughd@google.com, lokeshgidra@google.com, dancol@google.com, mhocko@kernel.org, akpm@linux-foundation.org, Andrey Ryabinin <aryabinin@virtuozzo.com>, Andy Lutomirski <luto@kernel.org>, anton.ivanov@kot-begemot.co.uk, Borislav Petkov <bp@alien8.de>, Catalin Marinas <catalin.marinas@arm.com>, Chris Zankel <chris@zankel.net>, Dave Hansen <dave.hansen@linux.intel.com>, "David S. Miller" <davem@davemloft.net>, elfring@users.sourceforge.net, Fenghua Yu <fenghua.yu@intel.com>, Geert Uytterhoeven <geert@linux-m68k.org>, Guan Xuetao <gxt@pku.edu.cn>, Helge Deller <deller@gmx.de>, Ingo Molnar <mingo@redhat.com>, "James E.J. Bottomley" <jejb@parisc-linux.org>, Jeff Dike <jdike@addtoit.com>, Jonas Bonn <jonas@southpole.se>, Julia Lawall <Julia.Lawall@lip6.fr>, kasan-dev@googlegroups.com, kvmarm@lists.cs.columbia.edu, Ley Foon Tan <lftan@altera.com>, linux-alpha@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@linux-mips.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-um@lists.infradead.org, linux-xtensa@linux-xtensa.org, Max Filippov <jcmvbkbc@gmail.com>, nios2-dev@lists.rocketboards.org, Peter Zijlstra <peterz@infradead.org>, Richard Weinberger <richard@nod.at>, Rich Felker <dalias@libc.org>, Sam Creasey <sammy@sammy.net>, sparclinux@vger.kernel.org, Stafford Horne <shorne@gmail.com>, Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>, Thomas Gleixner <tglx@linutronix.de>, Tony Luck <tony.luck@intel.com>, Will Deacon <will.deacon@arm.com>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>, Yoshinori Sato <ysato@users.sourceforge.jp>

On Wed, Oct 24, 2018 at 07:13:50PM -0700, Joel Fernandes wrote:
> On Wed, Oct 24, 2018 at 10:57:33PM +1100, Balbir Singh wrote:
> [...]
> > > > +		pmd_t pmd;
> > > > +
> > > > +		new_ptl = pmd_lockptr(mm, new_pmd);
> > 
> > 
> > Looks like this is largely inspired by move_huge_pmd(), I guess a lot of
> > the code applies, why not just reuse as much as possible? The same comments
> > w.r.t mmap_sem helping protect against lock order issues applies as well.
> 
> I thought about this and when I looked into it, it seemed there are subtle
> differences that make such sharing not worth it (or not possible).
>

Could you elaborate on them?

Thanks,
Balbir Singh.