From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 13 Dec 2018 17:04:00 -0500 From: Johannes Weiner To: Michal Hocko Cc: Andrew Morton , "Kirill A. Shutemov" , Liu Bo , Jan Kara , Dave Chinner , Theodore Ts'o , Vladimir Davydov , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, LKML , Shakeel Butt , Michal Hocko , Stable tree Subject: Re: [PATCH v3] mm, memcg: fix reclaim deadlock with writeback Message-ID: <20181213220400.GA9829@cmpxchg.org> References: <20181212155055.1269-1-mhocko@kernel.org> <20181213092221.27270-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181213092221.27270-1-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: On Thu, Dec 13, 2018 at 10:22:21AM +0100, Michal Hocko wrote: > From: Michal Hocko > > Liu Bo has experienced a deadlock between memcg (legacy) reclaim and the > ext4 writeback > task1: > [] wait_on_page_bit+0x82/0xa0 > [] shrink_page_list+0x907/0x960 > [] shrink_inactive_list+0x2c7/0x680 > [] shrink_node_memcg+0x404/0x830 > [] shrink_node+0xd8/0x300 > [] do_try_to_free_pages+0x10d/0x330 > [] try_to_free_mem_cgroup_pages+0xd5/0x1b0 > [] try_charge+0x14d/0x720 > [] memcg_kmem_charge_memcg+0x3c/0xa0 > [] memcg_kmem_charge+0x7e/0xd0 > [] __alloc_pages_nodemask+0x178/0x260 > [] alloc_pages_current+0x95/0x140 > [] pte_alloc_one+0x17/0x40 > [] __pte_alloc+0x1e/0x110 > [] alloc_set_pte+0x5fe/0xc20 > [] do_fault+0x103/0x970 > [] handle_mm_fault+0x61e/0xd10 > [] __do_page_fault+0x252/0x4d0 > [] do_page_fault+0x30/0x80 > [] page_fault+0x28/0x30 > [] 0xffffffffffffffff > > task2: > [] __lock_page+0x86/0xa0 > [] mpage_prepare_extent_to_map+0x2e7/0x310 [ext4] > [] ext4_writepages+0x479/0xd60 > [] do_writepages+0x1e/0x30 > [] __writeback_single_inode+0x45/0x320 > [] writeback_sb_inodes+0x272/0x600 > [] __writeback_inodes_wb+0x92/0xc0 > [] wb_writeback+0x268/0x300 > [] wb_workfn+0xb4/0x390 > [] process_one_work+0x189/0x420 > [] worker_thread+0x4e/0x4b0 > [] kthread+0xe6/0x100 > [] ret_from_fork+0x41/0x50 > [] 0xffffffffffffffff > > He adds > : task1 is waiting for the PageWriteback bit of the page that task2 has > : collected in mpd->io_submit->io_bio, and tasks2 is waiting for the LOCKED > : bit the page which tasks1 has locked. > > More precisely task1 is handling a page fault and it has a page locked > while it charges a new page table to a memcg. That in turn hits a memory > limit reclaim and the memcg reclaim for legacy controller is waiting on > the writeback but that is never going to finish because the writeback > itself is waiting for the page locked in the #PF path. So this is > essentially ABBA deadlock: > lock_page(A) > SetPageWriteback(A) > unlock_page(A) > lock_page(B) > lock_page(B) > pte_alloc_pne > shrink_page_list > wait_on_page_writeback(A) > SetPageWriteback(B) > unlock_page(B) > > # flush A, B to clear the writeback > > This accumulating of more pages to flush is used by several filesystems > to generate a more optimal IO patterns. > > Waiting for the writeback in legacy memcg controller is a workaround > for pre-mature OOM killer invocations because there is no dirty IO > throttling available for the controller. There is no easy way around > that unfortunately. Therefore fix this specific issue by pre-allocating > the page table outside of the page lock. We have that handy > infrastructure for that already so simply reuse the fault-around pattern > which already does this. > > There are probably other hidden __GFP_ACCOUNT | GFP_KERNEL allocations > from under a fs page locked but they should be really rare. I am not > aware of a better solution unfortunately. > > Reported-and-Debugged-by: Liu Bo > Cc: stable > Fixes: c3b94f44fcb0 ("memcg: further prevent OOM with too many dirty pages") > Signed-off-by: Michal Hocko Acked-by: Johannes Weiner Just one nit: > @@ -2993,6 +2993,17 @@ static vm_fault_t __do_fault(struct vm_fault *vmf) > struct vm_area_struct *vma = vmf->vma; > vm_fault_t ret; > > + /* > + * Preallocate pte before we take page_lock because this might lead to > + * deadlocks for memcg reclaim which waits for pages under writeback. > + */ > + if (pmd_none(*vmf->pmd) && !vmf->prealloc_pte) { > + vmf->prealloc_pte = pte_alloc_one(vmf->vma->vm_mm, vmf->address); > + if (!vmf->prealloc_pte) > + return VM_FAULT_OOM; > + smp_wmb(); /* See comment in __pte_alloc() */ > + } Could you be more specific in the deadlock comment? git blame will work fine for a while, but it becomes a pain to find corresponding patches after stuff gets moved around for years. In particular the race diagram between reclaim with a page lock held and the fs doing SetPageWriteback batches before kicking off IO would be useful directly in the code, IMO.