From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mikulas Patocka Subject: Re: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM Date: Fri, 20 Apr 2018 16:54:53 -0400 (EDT) Message-ID: 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" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180420130852.GC16083@dhcp22.suse.cz> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Michal Hocko Cc: dm-devel@redhat.com, eric.dumazet@gmail.com, mst@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, edumazet@google.com, bhutchings@solarflare.com, Andrew Morton , David Miller , Vlastimil Babka List-Id: virtualization@lists.linuxfoundation.org On Fri, 20 Apr 2018, Michal Hocko wrote: > On Thu 19-04-18 12:12:38, Mikulas Patocka wrote: > [...] > > From: Mikulas Patocka > > Subject: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM > > > > The kvmalloc function tries to use kmalloc and falls back to vmalloc if > > kmalloc fails. > > > > Unfortunatelly, some kernel code has bugs - it uses kvmalloc and then > > uses DMA-API on the returned memory or frees it with kfree. Such bugs were > > found in the virtio-net driver, dm-integrity or RHEL7 powerpc-specific > > code. > > > > These bugs are hard to reproduce because vmalloc falls back to kmalloc > > only if memory is fragmented. > > > > In order to detect these bugs reliably I submit this patch that changes > > kvmalloc to always use vmalloc if CONFIG_DEBUG_VM is turned on. > > 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. 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 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. 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. Mikulas