Return-Path: Received: from mx2.suse.de ([195.135.220.15]:42524 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726029AbeLGLUk (ORCPT ); Fri, 7 Dec 2018 06:20:40 -0500 Date: Fri, 7 Dec 2018 12:20:36 +0100 From: Michal Hocko To: Dave Chinner Cc: Jan Kara , Liu Bo , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH RFC] Ext4: fix deadlock on dirty pages between fault and writeback Message-ID: <20181207112036.GA1286@dhcp22.suse.cz> References: <1540858969-75803-1-git-send-email-bo.liu@linux.alibaba.com> <20181127114249.GH16301@quack2.suse.cz> <20181128201122.r4sec265cnlxgj2x@US-160370MP2.local> <20181129085238.GD31087@quack2.suse.cz> <20181129120253.GR6311@dastard> <20181129130002.GM31087@quack2.suse.cz> <20181129204019.GS6311@dastard> <20181205170656.GJ30615@quack2.suse.cz> <20181207052051.GB6311@dastard> <20181207071615.GO1286@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181207071615.GO1286@dhcp22.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri 07-12-18 08:16:15, Michal Hocko wrote: [...] > Memcg v1 indeed doesn't have any dirty IO throttling and this is a > poor's man workaround. We still do not have that AFAIK and I do not know > of an elegant way around that. Fortunatelly we shouldn't have that many > GFP_KERNEL | __GFP_ACCOUNT allocations under page lock and we can work > around this specific one quite easily. I haven't tested this yet but the > following should work > > diff --git a/mm/memory.c b/mm/memory.c > index 4ad2d293ddc2..59c98eeb0260 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2993,6 +2993,16 @@ 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 (!vmf->prealloc_pte) { > + vmf->prealloc_pte = pte_alloc_one(vmf->vma->vm>mm, vmf->address); > + if (!vmf->prealloc_pte) > + return VM_FAULT_OOM; > + } > + > ret = vma->vm_ops->fault(vmf); > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY | > VM_FAULT_DONE_COW))) This is too eager to allocate pte even when it is not really needed. Jack has also pointed out that I am missing a write barrier. So here we go with an updated patch. This is essentially what fault around code does. diff --git a/mm/memory.c b/mm/memory.c index 4ad2d293ddc2..1a73d2d4659e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -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() */ + } + ret = vma->vm_ops->fault(vmf); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY | VM_FAULT_DONE_COW))) -- Michal Hocko SUSE Labs