From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: "Joel Fernandes (Google)" Subject: [PATCH v2 2/2] mm: speed up mremap by 500x on large regions Date: Thu, 11 Oct 2018 18:37:56 -0700 Message-Id: <20181012013756.11285-2-joel@joelfernandes.org> In-Reply-To: <20181012013756.11285-1-joel@joelfernandes.org> References: <20181012013756.11285-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit To: linux-kernel@vger.kernel.org Cc: kernel-team@android.com, "Joel Fernandes (Google)" , minchan@kernel.org, pantin@google.com, hughd@google.com, lokeshgidra@google.com, dancol@google.com, mhocko@kernel.org, kirill@shutemov.name, akpm@linux-foundation.org, Andrey Ryabinin , Andy Lutomirski , Borislav Petkov , Catalin Marinas , Chris Zankel , Dave Hansen , "David S. Miller" , elfring@users.sourceforge.net, Fenghua Yu , Geert Uytterhoeven , Guan Xuetao , Helge Deller , Ingo Molnar , "James E.J. Bottomley" , Jeff Dike , Jonas Bonn , Julia Lawall , kasan-dev@googlegroups.com, kvmarm@lists.cs.columbia.edu, Ley Foon Tan , linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.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 , nios2-dev@lists.rocketboards.org, openrisc@lists.librecores.org, Peter Zijlstra , Richard Weinberger , Rich Felker , Sam Creasey , sparclinux@vger.kernel.org, Stafford Horne , Stefan Kristiansson , Thomas Gleixner , Tony Luck , Will Deacon , "maintainer:X86 ARCHITECTURE 32-BIT AND 64-BIT" , Yoshinori Sato List-ID: 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); + if (new_ptl != old_ptl) + spin_unlock(new_ptl); + spin_unlock(old_ptl); + + *need_flush = true; + return true; + } + return false; +} + unsigned long move_page_tables(struct vm_area_struct *vma, unsigned long old_addr, struct vm_area_struct *new_vma, unsigned long new_addr, unsigned long len, @@ -239,7 +287,21 @@ unsigned long move_page_tables(struct vm_area_struct *vma, split_huge_pmd(vma, old_pmd, old_addr); if (pmd_trans_unstable(old_pmd)) continue; + } else if (extent == PMD_SIZE) { + bool moved; + + /* See comment in move_ptes() */ + if (need_rmap_locks) + take_rmap_locks(vma); + moved = move_normal_pmd(vma, old_addr, new_addr, + old_end, old_pmd, new_pmd, + &need_flush); + if (need_rmap_locks) + drop_rmap_locks(vma); + if (moved) + continue; } + if (pte_alloc(new_vma->vm_mm, new_pmd)) break; next = (new_addr + PMD_SIZE) & PMD_MASK; -- 2.19.0.605.g01d371f741-goog