On Mon, May 22 2017 at 4:35pm -0400, David Rientjes <rientjes@xxxxxxxxxx> wrote: > On Mon, 22 May 2017, Mike Snitzer wrote: > > > > > The lvm2 was designed this way - it is broken, but there is not much that > > > > can be done about it - fixing this would mean major rewrite. The only > > > > thing we can do about it is to lower the deadlock probability with > > > > __GFP_HIGH (or PF_MEMALLOC that was used some times ago). > > > > Yes, lvm2 was originally designed to to have access to memory reserves > > to ensure forward progress. But if the mm subsystem has improved to > > allow for the required progress without lvm2 trying to stake a claim on > > those reserves then we'll gladly avoid (ab)using them. > > > > There is no such improvement to the page allocator when allocating at > runtime. A persistent amount of memory in a mempool could be set aside as > a preallocation and unavailable from the rest of the system forever as an > alternative to dynamically allocating with memory reserves, but that has > obvious downsides. This patch is the exact right thing to do. > > > > But let me repeat. GFP_KERNEL allocation for order-0 page will not fail. > > > > OK, but will it be serviced immediately? Not failing isn't useful if it > > never completes. > > > > No, and you can use __GFP_HIGH, which this patch does, to have a > reasonable expectation of forward progress in the very near term. > > > While adding the __GFP_NOFAIL flag would serve to document expectations > > I'm left unconvinced that the memory allocator will _not fail_ for an > > order-0 page -- as Mikulas said most ioctls don't need more than 4K. > > __GFP_NOFAIL would make no sense in kvmalloc() calls, ever, it would never > fallback to vmalloc :) > > I'm hoping this can get merged during the 4.12 window to fix the broken > commit d224e9381897. I've added your Acked-by and staged it for 4.12, please see: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-4.12/dm&id=8c1e2162f27b319da913683143c0c6c09b083ebb Not sure when I'll send it to Linus but certainly no later than for rc4 inclusion. Thanks, Mike -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
