From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) by kanga.kvack.org (Postfix) with ESMTP id 4E10D6B0006 for ; Fri, 12 Oct 2018 10:37:36 -0400 (EDT) Received: by mail-pg1-f200.google.com with SMTP id 17-v6so8968035pgs.18 for ; Fri, 12 Oct 2018 07:37:36 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id 1-v6sor1192797plx.17.2018.10.12.07.37.34 for (Google Transport Security); Fri, 12 Oct 2018 07:37:34 -0700 (PDT) Date: Fri, 12 Oct 2018 17:37:28 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH v2 2/2] mm: speed up mremap by 500x on large regions Message-ID: <20181012143728.t42uvr6etg7gp7fh@kshutemo-mobl1> References: <20181012013756.11285-1-joel@joelfernandes.org> <20181012013756.11285-2-joel@joelfernandes.org> <9ed82f9e-88c4-8e4f-8c45-3ef153469603@kot-begemot.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9ed82f9e-88c4-8e4f-8c45-3ef153469603@kot-begemot.co.uk> Sender: owner-linux-mm@kvack.org List-ID: To: Anton Ivanov Cc: "Joel Fernandes (Google)" , linux-kernel@vger.kernel.org, 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, linux-riscv@lists.infradead.org, elfring@users.sourceforge.net, Jonas Bonn , linux-s390@vger.kernel.org, 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, kvmarm@lists.cs.columbia.edu, Ingo Molnar , Geert Uytterhoeven , Andrey Ryabinin , linux-snps-arc@lists.infradead.org, kernel-team@android.com, Sam Creasey , Fenghua Yu , Jeff Dike , linux-um@lists.infradead.org, Stefan Kristiansson , Julia Lawall , linux-m68k@lists.linux-m68k.org, openrisc@lists.librecores.org, Borislav Petkov , Andy Lutomirski , nios2-dev@lists.rocketboards.org, Stafford Horne , Guan Xuetao , linux-arm-kernel@lists.infradead.org, Chris Zankel , Tony Luck , Richard Weinberger , linux-parisc@vger.kernel.org, pantin@google.com, Max Filippov , 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" On Fri, Oct 12, 2018 at 03:09:49PM +0100, Anton Ivanov wrote: > On 10/12/18 2:37 AM, Joel Fernandes (Google) wrote: > > Android needs to mremap large regions of memory during memory management > > related operations. The mremap system call can be really slow if THP is > > not enabled. The bottleneck is move_page_tables, which is copying each > > pte at a time, and can be really slow across a large map. Turning on THP > > may not be a viable option, and is not for us. This patch speeds up the > > performance for non-THP system by copying at the PMD level when possible. > > > > The speed up is three orders of magnitude. On a 1GB mremap, the mremap > > completion times drops from 160-250 millesconds to 380-400 microseconds. > > > > Before: > > Total mremap time for 1GB data: 242321014 nanoseconds. > > Total mremap time for 1GB data: 196842467 nanoseconds. > > Total mremap time for 1GB data: 167051162 nanoseconds. > > > > After: > > Total mremap time for 1GB data: 385781 nanoseconds. > > Total mremap time for 1GB data: 388959 nanoseconds. > > Total mremap time for 1GB data: 402813 nanoseconds. > > > > Incase THP is enabled, the optimization is skipped. I also flush the > > tlb every time we do this optimization since I couldn't find a way to > > determine if the low-level PTEs are dirty. It is seen that the cost of > > doing so is not much compared the improvement, on both x86-64 and arm64. > > > > Cc: minchan@kernel.org > > Cc: pantin@google.com > > Cc: hughd@google.com > > Cc: lokeshgidra@google.com > > Cc: dancol@google.com > > Cc: mhocko@kernel.org > > Cc: kirill@shutemov.name > > Cc: akpm@linux-foundation.org > > Signed-off-by: Joel Fernandes (Google) > > --- > > mm/mremap.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 62 insertions(+) > > > > diff --git a/mm/mremap.c b/mm/mremap.c > > index 9e68a02a52b1..d82c485822ef 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) { > > + pmd_t pmd; > > + > > + new_ptl = pmd_lockptr(mm, new_pmd); > > + if (new_ptl != old_ptl) > > + spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); > > + > > + /* Clear the pmd */ > > + pmd = *old_pmd; > > + pmd_clear(old_pmd); > > + > > + VM_BUG_ON(!pmd_none(*new_pmd)); > > + > > + /* Set the new pmd */ > > + set_pmd_at(mm, new_addr, new_pmd, pmd); > > UML does not have set_pmd_at at all Every architecture does. :) But it may come not from the arch code. > If I read the code right, MIPS completely ignores the address argument so > set_pmd_at there may not have the effect which this patch is trying to > achieve. Ignoring address is fine. Most architectures do that.. The ideas is to move page table to the new pmd slot. It's nothing to do with the address passed to set_pmd_at(). -- Kirill A. Shutemov