From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by kanga.kvack.org (Postfix) with ESMTP id CA0C56B0006 for ; Fri, 12 Oct 2018 17:40:15 -0400 (EDT) Received: by mail-pg1-f199.google.com with SMTP id x2-v6so10262297pgr.8 for ; Fri, 12 Oct 2018 14:40:15 -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 c2-v6sor2126896pll.61.2018.10.12.14.40.14 for (Google Transport Security); Fri, 12 Oct 2018 14:40:14 -0700 (PDT) Date: Sat, 13 Oct 2018 00:40:08 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH v2 2/2] mm: speed up mremap by 500x on large regions Message-ID: <20181012214008.jj7vhh76vte7xj7i@kshutemo-mobl1> References: <20181012013756.11285-1-joel@joelfernandes.org> <20181012013756.11285-2-joel@joelfernandes.org> <9ed82f9e-88c4-8e4f-8c45-3ef153469603@kot-begemot.co.uk> <20181012143728.t42uvr6etg7gp7fh@kshutemo-mobl1> <4dd52e22-5b51-9b30-7178-fde603a08f88@kot-begemot.co.uk> <97cb3fe1-7bc1-12ff-d602-56c72a5496c5@kot-begemot.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <97cb3fe1-7bc1-12ff-d602-56c72a5496c5@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 05:42:24PM +0100, Anton Ivanov wrote: > > On 10/12/18 3:48 PM, Anton Ivanov wrote: > > On 12/10/2018 15:37, Kirill A. Shutemov wrote: > > > 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. :) > > > > I tried to build it patching vs 4.19-rc before I made this statement and > > ran into that. > > > > Presently it does not. > > > > https://elixir.bootlin.com/linux/v4.19-rc7/ident/set_pmd_at - UML is not > > on the list. > > Once this problem as well as the omissions in the include changes for UML in > patch one have been fixed it appears to be working. > > What it needs is attached. Well, the optization is only suitable for arch that has 3 or more levels of page tables. Otherwise it will not have [non-folded] pmd. And in this case arch/um already should have set_pmd_at(), see 3_LEVEL_PGTABLES. To port on 2-level paging, it has to be handled on pgd level. It complicates the code and will not bring much value. -- Kirill A. Shutemov