Michal Hocko wrote: > 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 We made many memory allocation requests from page fault path (e.g. XFS) __GFP_FS some time ago, didn't we? But if I recall correctly (I couldn't find the message), there are some allocation requests from page fault path which cannot use __GFP_FS. Then, not all allocation requests can call oom_kill_process() and reaching pagefault_out_of_memory() will be inevitable. > 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. If we carry a flag via task_struct that indicates whether it is an memory allocation request from page fault and allocation failure is not acceptable, we can call out_of_memory() from page allocator path. > - if (!mutex_trylock(&oom_lock)) > + if (fatal_signal_pending) fatal_signal_pending(current) By the way, can page fault occur after reaching do_exit()? When a thread reached do_exit(), fatal_signal_pending(current) becomes false, doesn't it? -- 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>
