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Message-ID: <CAPcyv4hvk8rfV_=5EX3QPFLZ=LB4=hWG5h4Z42koNYim9DB3FQ@mail.gmail.com> Date: Fri, 1 Dec 2017 08:29:53 -0800 From: Dan Williams <dan.j.williams@...el.com> To: Jason Gunthorpe <jgg@...pe.ca> Cc: Michal Hocko <mhocko@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Linux MM <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Christoph Hellwig <hch@....de>, "stable@...r.kernel.org" <stable@...r.kernel.org>, "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>, linux-rdma <linux-rdma@...r.kernel.org> Subject: Re: [PATCH v3 1/4] mm: introduce get_user_pages_longterm On Fri, Dec 1, 2017 at 8:02 AM, Jason Gunthorpe <jgg@...pe.ca> wrote: > > On Fri, Dec 01, 2017 at 11:12:18AM +0100, Michal Hocko wrote: > > On Thu 30-11-17 12:01:17, Jason Gunthorpe wrote: > > > On Thu, Nov 30, 2017 at 10:32:42AM -0800, Dan Williams wrote: > > > > > Who and how many LRU pages can pin that way and how do you prevent nasty > > > > > users to DoS systems this way? > > > > > > > > I assume this is something the RDMA community has had to contend with? > > > > I'm not an RDMA person, I'm just here to fix dax. > > > > > > The RDMA implementation respects the mlock rlimit > > > > OK, so then I am kind of lost in why do we need a special g-u-p variant. > > The documentation doesn't say and quite contrary it assumes that the > > caller knows what he is doing. This cannot be the right approach. > > I thought it was because get_user_pages_longterm is supposed to fail > on DAX mappings? Correct, the rlimit checks are a separate issue, get_user_pages_longterm is only there to avoid open coding vma lookup and vma_is_fsdax() checks in multiple code paths. > And maybe we should think about moving the rlimit accounting into this > new function too someday? DAX pages are not accounted in any rlimit because they are statically allocated reserved memory regions.
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