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Shutemov" To: Balbir Singh Subject: Re: [PATCH 2/4] mm: speed up mremap by 500x on large regions (v2) Message-ID: <20181024125724.yf6frdimjulf35do@kshutemo-mobl1> References: <20181013013200.206928-1-joel@joelfernandes.org> <20181013013200.206928-3-joel@joelfernandes.org> <20181024101255.it4lptrjogalxbey@kshutemo-mobl1> <20181024115733.GN8537@350D> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181024115733.GN8537@350D> User-Agent: NeoMutt/20180716 X-Mailman-Approved-At: Thu, 25 Oct 2018 00:18:02 +1100 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-mips@linux-mips.org, Rich Felker , linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , Catalin Marinas , Dave Hansen , Will Deacon , mhocko@kernel.org, linux-mm@kvack.org, lokeshgidra@google.com, "Joel Fernandes \(Google\)" , linux-riscv@lists.infradead.org, elfring@users.sourceforge.net, Jonas Bonn , kvmarm@lists.cs.columbia.edu, dancol@google.com, Yoshinori Sato , sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-hexagon@vger.kernel.org, Helge Deller , "maintainer:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" , hughd@google.com, "James E.J. Bottomley" , kasan-dev@googlegroups.com, anton.ivanov@kot-begemot.co.uk, Ingo Molnar , Geert Uytterhoeven , Andrey Ryabinin , linux-snps-arc@lists.infradead.org, kernel-team@android.com, Sam Creasey , Fenghua Yu , linux-s390@vger.kernel.org, Jeff Dike , linux-um@lists.infradead.org, Stefan Kristiansson , Julia Lawall , linux-m68k@lists.linux-m68k.org, Borislav Petkov , Andy Lutomirski , nios2-dev@lists.rocketboards.org, Stafford Horne , Guan Xuetao , Chris Zankel , Tony Luck , Richard Weinberger , linux-parisc@vger.kernel.org, pantin@google.com, Max Filippov , linux-kernel@vger.kernel.org, minchan@kernel.org, Thomas Gleixner , linux-alpha@vger.kernel.org, Ley Foon Tan , akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, "David S. Miller" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Oct 24, 2018 at 10:57:33PM +1100, Balbir Singh wrote: > On Wed, Oct 24, 2018 at 01:12:56PM +0300, Kirill A. Shutemov wrote: > > On Fri, Oct 12, 2018 at 06:31:58PM -0700, Joel Fernandes (Google) wrote: > > > diff --git a/mm/mremap.c b/mm/mremap.c > > > index 9e68a02a52b1..2fd163cff406 100644 > > > --- a/mm/mremap.c > > > +++ b/mm/mremap.c > > > @@ -191,6 +191,54 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, > > > drop_rmap_locks(vma); > > > } > > > > > > +static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr, > > > + unsigned long new_addr, unsigned long old_end, > > > + pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush) > > > +{ > > > + spinlock_t *old_ptl, *new_ptl; > > > + struct mm_struct *mm = vma->vm_mm; > > > + > > > + if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK) > > > + || old_end - old_addr < PMD_SIZE) > > > + return false; > > > + > > > + /* > > > + * The destination pmd shouldn't be established, free_pgtables() > > > + * should have release it. > > > + */ > > > + if (WARN_ON(!pmd_none(*new_pmd))) > > > + return false; > > > + > > > + /* > > > + * We don't have to worry about the ordering of src and dst > > > + * ptlocks because exclusive mmap_sem prevents deadlock. > > > + */ > > > + old_ptl = pmd_lock(vma->vm_mm, old_pmd); > > > + if (old_ptl) { > > > > How can it ever be false? > > > > > + 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. pmd_lock() cannot fail, but __pmd_trans_huge_lock() can. We should not copy the code blindly. -- Kirill A. Shutemov