On Fri 01-12-17 08:29:53, Dan Williams wrote: > On Fri, Dec 1, 2017 at 8:02 AM, Jason Gunthorpe <jgg@xxxxxxxx> 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. Then it is a terrible misnomer. One would expect this is a proper way to get a longterm pin on a page. > > 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. Which is OK, but how do you prevent anybody calling this function on normal LRU pages? -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
