On Thu, Jun 08, 2017 at 04:36:07PM +0200, Michal Hocko wrote: > Does anybody see any problem with the patch or I can send it for the > inclusion? > > On Fri 19-05-17 13:26:04, Michal Hocko wrote: > > From: Michal Hocko <mhocko@xxxxxxxx> > > > > Any allocation failure during the #PF path will return with VM_FAULT_OOM > > which in turn results in pagefault_out_of_memory. This can happen for > > 2 different reasons. a) Memcg is out of memory and we rely on > > mem_cgroup_oom_synchronize to perform the memcg OOM handling or b) > > normal allocation fails. > > > > The later is quite problematic because allocation paths already trigger > > out_of_memory and the page allocator tries really hard to not fail > > allocations. Anyway, if the OOM killer has been already invoked there > > is no reason to invoke it again from the #PF path. Especially when the > > OOM condition might be gone by that time and we have no way to find out > > other than allocate. > > > > Moreover if the allocation failed and the OOM killer hasn't been > > invoked then we are unlikely to do the right thing from the #PF context > > because we have already lost the allocation context and restictions and > > therefore might oom kill a task from a different NUMA domain. > > > > An allocation might fail also when the current task is the oom victim > > and there are no memory reserves left and we should simply bail out > > from the #PF rather than invoking out_of_memory. > > > > This all suggests that there is no legitimate reason to trigger > > out_of_memory from pagefault_out_of_memory so drop it. Just to be sure > > that no #PF path returns with VM_FAULT_OOM without allocation print a > > warning that this is happening before we restart the #PF. > > > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> I don't agree with this patch. The warning you replace the oom call with indicates that we never expect a VM_FAULT_OOM to leak to this point. But should there be a leak, it's infinitely better to tickle the OOM killer again - even if that call is then fairly inaccurate and without alloc context - than infinite re-invocations of the #PF when the VM_FAULT_OOM comes from a context - existing or future - that isn't allowed to trigger the OOM. I'm not a fan of defensive programming, but is this call to OOM more expensive than the printk() somehow? And how certain are you that no VM_FAULT_OOMs will leak, given how spread out page fault handlers and how complex the different allocation contexts inside them are? -- 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>
