From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [RFC 6/7] mm: extend process_madvise syscall to support vector arrary Date: Tue, 21 May 2019 08:24:21 +0200 Message-ID: <20190521062421.GD32329@dhcp22.suse.cz> References: <20190520035254.57579-1-minchan@kernel.org> <20190520035254.57579-7-minchan@kernel.org> <20190520092258.GZ6836@dhcp22.suse.cz> <20190521024820.GG10039@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190521024820.GG10039@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Minchan Kim Cc: Andrew Morton , LKML , linux-mm , Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org On Tue 21-05-19 11:48:20, Minchan Kim wrote: > On Mon, May 20, 2019 at 11:22:58AM +0200, Michal Hocko wrote: > > [Cc linux-api] > > > > On Mon 20-05-19 12:52:53, Minchan Kim wrote: > > > Currently, process_madvise syscall works for only one address range > > > so user should call the syscall several times to give hints to > > > multiple address range. > > > > Is that a problem? How big of a problem? Any numbers? > > We easily have 2000+ vma so it's not trivial overhead. I will come up > with number in the description at respin. Does this really have to be a fast operation? I would expect the monitor is by no means a fast path. The system call overhead is not what it used to be, sigh, but still for something that is not a hot path it should be tolerable, especially when the whole operation is quite expensive on its own (wrt. the syscall entry/exit). I am not saying we do not need a multiplexing API, I am just not sure we need it right away. Btw. there was some demand for other MM syscalls to provide a multiplexing API (e.g. mprotect), maybe it would be better to handle those in one go? -- Michal Hocko SUSE Labs