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Shutemov" , Kirill Tkhai , Andrew Morton , LKML , linux-mm , linux-api@vger.kernel.org, oleksandr@redhat.com, Suren Baghdasaryan , Tim Murray , Daniel Colascione , Sandeep Patil , Sonny Rao , Brian Geffon , Johannes Weiner , Shakeel Butt , John Dias , christian.brauner@ubuntu.com, sjpark@amazon.de Subject: Re: [PATCH v2 2/5] mm: introduce external memory hinting API Message-ID: <20200121184329.GG140922@google.com> References: <20200116235953.163318-1-minchan@kernel.org> <20200116235953.163318-3-minchan@kernel.org> <20200117115225.GV19428@dhcp22.suse.cz> <20200120112722.GY18451@dhcp22.suse.cz> <20200120123935.onlls7enjtzenbvt@box> <20200120132405.GF18451@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200120132405.GF18451@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jan 20, 2020 at 02:24:05PM +0100, Michal Hocko wrote: > On Mon 20-01-20 15:39:35, Kirill A. Shutemov wrote: > > On Mon, Jan 20, 2020 at 12:27:22PM +0100, Michal Hocko wrote: > > > On Mon 20-01-20 13:24:35, Kirill Tkhai wrote: > [...] > > > > Even two threads on common memory need a synchronization > > > > to manage mappings in a sane way. Managing memory from two processes > > > > is the same in principle, and the only difference is that another level > > > > of synchronization is required. > > > > > > Well, not really. The operation might simply attempt to perform an > > > operation on a specific memory area and get a failure if it doesn't > > > reference the same object anymore. What I think we need is some form of > > > a handle to operate on. In the past we have discussed several > > > directions. I was proposing /proc/self/map_anon/ (analogous to > > > map_files) where you could inspect anonymous memory and get a file > > > handle for it. madvise would then operate on the fd and then there > > > shouldn't be a real problem to revalidate that the object is still > > > valid. But there was no general enthusiasm about that approach. There > > > are likely some land mines on the way. > > > > Converting anon memory to file-backed is bad idea and going to backfire. > > I didn't mean to convert. I meant to expose that information via proc > the same way we do for file backed mappings. That shouldn't really > require to re-design the way how anonymous vma work IMO. But I haven't > tried that so there might be many gotchas there. > > There are obvious things to think about though. Such fd cannot be sent > to other processes (SCM stuff), mmap of the file would have to be > disallowed and many others I am not aware of. I am not even pushing this > direction because I am not convinced about how viable it is myself. But > it would sound like a nice extension of the existing mechanism we have > and a file based madvise sounds attractive to me as well because we > already have that. I am not a fan of fd based approach but I already reserved last argument of the API as extendable field so we could use the field as "fd" when we really need that kinds of fine-grained synchronization model if it's not enough with SGISTOP, freezer and so.