From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753694AbdHUC0P (ORCPT ); Sun, 20 Aug 2017 22:26:15 -0400 Received: from mail-pg0-f48.google.com ([74.125.83.48]:37167 "EHLO mail-pg0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753665AbdHUC0N (ORCPT ); Sun, 20 Aug 2017 22:26:13 -0400 Date: Mon, 21 Aug 2017 11:26:29 +0900 From: Sergey Senozhatsky To: Laurent Dufour Cc: paulmck@linux.vnet.ibm.com, peterz@infradead.org, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org Subject: Re: [PATCH v2 00/20] Speculative page faults Message-ID: <20170821022629.GA541@jagdpanzerIV.localdomain> References: <1503007519-26777-1-git-send-email-ldufour@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1503007519-26777-1-git-send-email-ldufour@linux.vnet.ibm.com> User-Agent: Mutt/1.8.3 (2017-05-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On (08/18/17 00:04), Laurent Dufour wrote: > This is a port on kernel 4.13 of the work done by Peter Zijlstra to > handle page fault without holding the mm semaphore [1]. > > The idea is to try to handle user space page faults without holding the > mmap_sem. This should allow better concurrency for massively threaded > process since the page fault handler will not wait for other threads memory > layout change to be done, assuming that this change is done in another part > of the process's memory space. This type page fault is named speculative > page fault. If the speculative page fault fails because of a concurrency is > detected or because underlying PMD or PTE tables are not yet allocating, it > is failing its processing and a classic page fault is then tried. > > The speculative page fault (SPF) has to look for the VMA matching the fault > address without holding the mmap_sem, so the VMA list is now managed using > SRCU allowing lockless walking. The only impact would be the deferred file > derefencing in the case of a file mapping, since the file pointer is > released once the SRCU cleaning is done. This patch relies on the change > done recently by Paul McKenney in SRCU which now runs a callback per CPU > instead of per SRCU structure [1]. > > The VMA's attributes checked during the speculative page fault processing > have to be protected against parallel changes. This is done by using a per > VMA sequence lock. This sequence lock allows the speculative page fault > handler to fast check for parallel changes in progress and to abort the > speculative page fault in that case. > > Once the VMA is found, the speculative page fault handler would check for > the VMA's attributes to verify that the page fault has to be handled > correctly or not. Thus the VMA is protected through a sequence lock which > allows fast detection of concurrent VMA changes. If such a change is > detected, the speculative page fault is aborted and a *classic* page fault > is tried. VMA sequence locks are added when VMA attributes which are > checked during the page fault are modified. > > When the PTE is fetched, the VMA is checked to see if it has been changed, > so once the page table is locked, the VMA is valid, so any other changes > leading to touching this PTE will need to lock the page table, so no > parallel change is possible at this time. [ 2311.315400] ====================================================== [ 2311.315401] WARNING: possible circular locking dependency detected [ 2311.315403] 4.13.0-rc5-next-20170817-dbg-00039-gaf11d7500492-dirty #1743 Not tainted [ 2311.315404] ------------------------------------------------------ [ 2311.315406] khugepaged/43 is trying to acquire lock: [ 2311.315407] (&mapping->i_mmap_rwsem){++++}, at: [] rmap_walk_file+0x5a/0x147 [ 2311.315415] but task is already holding lock: [ 2311.315416] (fs_reclaim){+.+.}, at: [] fs_reclaim_acquire+0x12/0x35 [ 2311.315420] which lock already depends on the new lock. [ 2311.315422] the existing dependency chain (in reverse order) is: [ 2311.315423] -> #3 (fs_reclaim){+.+.}: [ 2311.315427] fs_reclaim_acquire+0x32/0x35 [ 2311.315429] __alloc_pages_nodemask+0x8d/0x217 [ 2311.315432] pte_alloc_one+0x13/0x5e [ 2311.315434] __pte_alloc+0x1f/0x83 [ 2311.315436] move_page_tables+0x2c9/0x5ac [ 2311.315438] move_vma.isra.25+0xff/0x2a2 [ 2311.315439] SyS_mremap+0x41b/0x49e [ 2311.315442] entry_SYSCALL_64_fastpath+0x18/0xad [ 2311.315443] -> #2 (&vma->vm_sequence/1){+.+.}: [ 2311.315449] write_seqcount_begin_nested+0x1b/0x1d [ 2311.315451] __vma_adjust+0x1b7/0x5d6 [ 2311.315453] __split_vma+0x142/0x1a3 [ 2311.315454] do_munmap+0x128/0x2af [ 2311.315455] vm_munmap+0x5a/0x73 [ 2311.315458] elf_map+0xb1/0xce [ 2311.315459] load_elf_binary+0x8e0/0x1348 [ 2311.315462] search_binary_handler+0x70/0x1f3 [ 2311.315464] load_script+0x1a6/0x1b5 [ 2311.315466] search_binary_handler+0x70/0x1f3 [ 2311.315468] do_execveat_common+0x461/0x691 [ 2311.315471] kernel_init+0x5a/0xf0 [ 2311.315472] ret_from_fork+0x27/0x40 [ 2311.315473] -> #1 (&vma->vm_sequence){+.+.}: [ 2311.315478] write_seqcount_begin_nested+0x1b/0x1d [ 2311.315480] __vma_adjust+0x19c/0x5d6 [ 2311.315481] __split_vma+0x142/0x1a3 [ 2311.315482] do_munmap+0x128/0x2af [ 2311.315484] vm_munmap+0x5a/0x73 [ 2311.315485] elf_map+0xb1/0xce [ 2311.315487] load_elf_binary+0x8e0/0x1348 [ 2311.315489] search_binary_handler+0x70/0x1f3 [ 2311.315490] load_script+0x1a6/0x1b5 [ 2311.315492] search_binary_handler+0x70/0x1f3 [ 2311.315494] do_execveat_common+0x461/0x691 [ 2311.315496] kernel_init+0x5a/0xf0 [ 2311.315497] ret_from_fork+0x27/0x40 [ 2311.315498] -> #0 (&mapping->i_mmap_rwsem){++++}: [ 2311.315503] lock_acquire+0x176/0x19e [ 2311.315505] down_read+0x3b/0x55 [ 2311.315507] rmap_walk_file+0x5a/0x147 [ 2311.315508] page_referenced+0x11c/0x134 [ 2311.315511] shrink_page_list+0x36b/0xb80 [ 2311.315512] shrink_inactive_list+0x1d9/0x437 [ 2311.315514] shrink_node_memcg.constprop.71+0x3e7/0x571 [ 2311.315515] shrink_node+0x3f/0x149 [ 2311.315517] try_to_free_pages+0x270/0x45f [ 2311.315518] __alloc_pages_slowpath+0x34a/0xaa2 [ 2311.315520] __alloc_pages_nodemask+0x111/0x217 [ 2311.315523] khugepaged_alloc_page+0x17/0x45 [ 2311.315524] khugepaged+0xa29/0x16b5 [ 2311.315527] kthread+0xfb/0x103 [ 2311.315529] ret_from_fork+0x27/0x40 [ 2311.315530] other info that might help us debug this: [ 2311.315531] Chain exists of: &mapping->i_mmap_rwsem --> &vma->vm_sequence/1 --> fs_reclaim [ 2311.315537] Possible unsafe locking scenario: [ 2311.315538] CPU0 CPU1 [ 2311.315539] ---- ---- [ 2311.315540] lock(fs_reclaim); [ 2311.315542] lock(&vma->vm_sequence/1); [ 2311.315545] lock(fs_reclaim); [ 2311.315547] lock(&mapping->i_mmap_rwsem); [ 2311.315549] *** DEADLOCK *** [ 2311.315551] 1 lock held by khugepaged/43: [ 2311.315552] #0: (fs_reclaim){+.+.}, at: [] fs_reclaim_acquire+0x12/0x35 [ 2311.315556] stack backtrace: [ 2311.315559] CPU: 0 PID: 43 Comm: khugepaged Not tainted 4.13.0-rc5-next-20170817-dbg-00039-gaf11d7500492-dirty #1743 [ 2311.315560] Call Trace: [ 2311.315564] dump_stack+0x67/0x8e [ 2311.315568] print_circular_bug.isra.39+0x1c7/0x1d4 [ 2311.315570] __lock_acquire+0xb1a/0xe06 [ 2311.315572] ? graph_unlock+0x69/0x69 [ 2311.315575] lock_acquire+0x176/0x19e [ 2311.315577] ? rmap_walk_file+0x5a/0x147 [ 2311.315579] down_read+0x3b/0x55 [ 2311.315581] ? rmap_walk_file+0x5a/0x147 [ 2311.315583] rmap_walk_file+0x5a/0x147 [ 2311.315585] page_referenced+0x11c/0x134 [ 2311.315587] ? page_vma_mapped_walk_done.isra.15+0xb/0xb [ 2311.315589] ? page_get_anon_vma+0x6d/0x6d [ 2311.315591] shrink_page_list+0x36b/0xb80 [ 2311.315593] ? _raw_spin_unlock_irq+0x29/0x46 [ 2311.315595] shrink_inactive_list+0x1d9/0x437 [ 2311.315597] shrink_node_memcg.constprop.71+0x3e7/0x571 [ 2311.315600] shrink_node+0x3f/0x149 [ 2311.315602] try_to_free_pages+0x270/0x45f [ 2311.315604] __alloc_pages_slowpath+0x34a/0xaa2 [ 2311.315608] ? ___might_sleep+0xd5/0x234 [ 2311.315609] __alloc_pages_nodemask+0x111/0x217 [ 2311.315612] khugepaged_alloc_page+0x17/0x45 [ 2311.315613] khugepaged+0xa29/0x16b5 [ 2311.315616] ? remove_wait_queue+0x47/0x47 [ 2311.315618] ? collapse_shmem.isra.43+0x882/0x882 [ 2311.315620] kthread+0xfb/0x103 [ 2311.315622] ? __list_del_entry+0x1d/0x1d [ 2311.315624] ret_from_fork+0x27/0x40 -ss