On Fri, 20 Apr 2018, Michal Hocko wrote:
> On Thu 19-04-18 12:12:38, Mikulas Patocka wrote: > [...] > > From: Mikulas Patocka <mpato...@redhat.com> > > 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
