From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM Date: Fri, 20 Apr 2018 14:02:00 -0700 Message-ID: <20180420210200.GH10788@bombadil.infradead.org> References: <3e65977e-53cd-bf09-bc4b-0ce40e9091fe@gmail.com> <20180418.134651.2225112489265654270.davem@davemloft.net> <20180420130852.GC16083@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Michal Hocko , David Miller , Andrew Morton , linux-mm@kvack.org, eric.dumazet@gmail.com, edumazet@google.com, bhutchings@solarflare.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com, jasowang@redhat.com, virtualization@lists.linux-foundation.org, dm-devel@redhat.com, Vlastimil Babka To: Mikulas Patocka Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Apr 20, 2018 at 04:54:53PM -0400, Mikulas Patocka wrote: > On Fri, 20 Apr 2018, Michal Hocko wrote: > > No way. This is just wrong! First of all, you will explode most likely > > on many allocations of small sizes. Second, CONFIG_DEBUG_VM tends to be > > enabled quite often. > > You're an evil person who doesn't want to fix bugs. Steady on. There's no need for that. Michal isn't evil. Please apologise. > You refused to fix vmalloc(GFP_NOIO) misbehavior a year ago (did you make > some progress with it since that time?) and you refuse to fix kvmalloc > misuses. I understand you're frustrated, but this is not the way to get the problems fixed. > I tried this patch on text-only virtual machine and /proc/vmallocinfo > shows 614kB more memory. I tried it on a desktop machine with the chrome > browser open and /proc/vmallocinfo space is increased by 7MB. So no - this > won't exhaust memory and kill the machine. This is good data, thank you for providing it. > Arguing that this increases memory consumption is as bogus as arguing that > CONFIG_LOCKDEP increses memory consumption. No one is forcing you to > enable CONFIG_LOCKDEP and no one is forcing you to enable this kvmalloc > test too. I think there's a real problem which is that CONFIG_DEBUG_VM is too broad. It inserts code in a *lot* of places, some of which is quite expensive. We would do better to split it into more granular pieces ... although an explosion of configuration options isn't great either. Maybe just CONFIG_DEBUG_VM and CONFIG_DEBUG_VM_EXPENSIVE. Michal may be wrong, but he's not evil.