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Date: Thu, 5 Oct 2017 16:32:07 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Laurent Dufour <ldufour@...ux.vnet.ibm.com> Cc: Paul McKenney <paulmck@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>, kirill@...temov.name, Andi Kleen <ak@...ux.intel.com>, Michal Hocko <mhocko@...nel.org>, dave@...olabs.net, Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Michael Ellerman <mpe@...erman.id.au>, Paul Mackerras <paulus@...ba.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Will Deacon <will.deacon@....com>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, haren@...ux.vnet.ibm.com, Anshuman Khandual <khandual@...ux.vnet.ibm.com>, npiggin@...il.com, bsingharora@...il.com, Tim Chen <tim.c.chen@...ux.intel.com>, linuxppc-dev@...ts.ozlabs.org, "x86@...nel.org" <x86@...nel.org> Subject: Re: [PATCH v3 00/20] Speculative page faults On Wed, Oct 04, 2017 at 08:50:49AM +0200, Laurent Dufour wrote: > On 25/09/2017 18:27, Alexei Starovoitov wrote: > > On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour > > <ldufour@...ux.vnet.ibm.com> wrote: > >> Despite the unprovable lockdep warning raised by Sergey, I didn't get any > >> feedback on this series. > >> > >> Is there a chance to get it moved upstream ? > > > > what is the status ? > > We're eagerly looking forward for this set to land, > > since we have several use cases for tracing that > > will build on top of this set as discussed at Plumbers. > > Hi Alexei, > > Based on Plumber's note [1], it sounds that the use case is tied to the BPF > tracing where a call tp find_vma() call will be made on a process's context > to fetch user space's symbols. > > Am I right ? > Is the find_vma() call made in the context of the process owning the mm > struct ? Hi Laurent, we're thinking about several use cases on top of your work. First one is translation of user address to file_handle where we need to do find_vma() from preempt_disabled context of bpf program. My understanding that srcu should solve that nicely. Second is making probe_read() to try harder when address is causing minor fault. We're thinking that find_vma() followed by some new light weight filemap_access() that doesn't sleep will do the trick. In both cases the program will be accessing current->mm
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