From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f198.google.com (mail-pl1-f198.google.com [209.85.214.198]) by kanga.kvack.org (Postfix) with ESMTP id DEB136B0006 for ; Tue, 9 Oct 2018 16:14:41 -0400 (EDT) Received: by mail-pl1-f198.google.com with SMTP id b23-v6so2285665pls.8 for ; Tue, 09 Oct 2018 13:14:41 -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 v16-v6sor16134843plo.4.2018.10.09.13.14.40 for (Google Transport Security); Tue, 09 Oct 2018 13:14:40 -0700 (PDT) From: "Joel Fernandes (Google)" Subject: [PATCH] mm: Speed up mremap on large regions Date: Tue, 9 Oct 2018 13:14:00 -0700 Message-Id: <20181009201400.168705-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: kernel-team@android.com, Joel Fernandes , minchan@google.com, hughd@google.com, lokeshgidra@google.com, Andrew Morton , Greg Kroah-Hartman , Kate Stewart , Philippe Ombredanne , Thomas Gleixner 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@google.com Cc: hughd@google.com Cc: lokeshgidra@google.com Cc: kernel-team@android.com 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 5c2e18505f75..68ddc9e9dfde 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); } +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, new_addr)) break; next = (new_addr + PMD_SIZE) & PMD_MASK; -- 2.19.0.605.g01d371f741-goog