From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by kanga.kvack.org (Postfix) with ESMTP id 1F2556B0003 for ; Fri, 12 Oct 2018 10:49:17 -0400 (EDT) Received: by mail-wm1-f70.google.com with SMTP id y199-v6so7089389wmc.6 for ; Fri, 12 Oct 2018 07:49:17 -0700 (PDT) Received: from www.kot-begemot.co.uk (ivanoab6.miniserver.com. [5.153.251.140]) by mx.google.com with ESMTPS id r3-v6si1278448wmh.39.2018.10.12.07.49.15 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 12 Oct 2018 07:49:15 -0700 (PDT) Subject: Re: [PATCH v2 2/2] mm: speed up mremap by 500x on large regions 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> From: Anton Ivanov Message-ID: <4dd52e22-5b51-9b30-7178-fde603a08f88@kot-begemot.co.uk> Date: Fri, 12 Oct 2018 15:48:15 +0100 MIME-Version: 1.0 In-Reply-To: <20181012143728.t42uvr6etg7gp7fh@kshutemo-mobl1> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" 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 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. > > But it may come not from the arch code. There is no generic definition as far as I can see. All 12 defines in 4.19 are in arch specific code. Unless i am missing something... > >> 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(). If that is it's only function, then I am going to appropriate the code out of the MIPS tree for further uml testing. It does exactly that - just move the pmd the new slot. > A.