Michal Hocko wrote: > On Tue 29-03-16 15:13:54, David Rientjes wrote: > > On Tue, 29 Mar 2016, Michal Hocko wrote: > > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > > index 86349586eacb..1c2b7a82f0c4 100644 > > > --- a/mm/oom_kill.c > > > +++ b/mm/oom_kill.c > > > @@ -876,6 +876,10 @@ bool out_of_memory(struct oom_control *oc) > > > return true; > > > } > > > > > > + /* The OOM killer does not compensate for IO-less reclaim. */ > > > + if (!(oc->gfp_mask & __GFP_FS)) > > > + return true; > > > + This patch will disable pagefault_out_of_memory() because currently pagefault_out_of_memory() is passing oc->gfp_mask == 0. Because of current behavior, calling oom notifiers from !__GFP_FS seems to be safe. > > > /* > > > * Check if there were limitations on the allocation (only relevant for > > > * NUMA) that may require different handling. > > > > I don't object to this necessarily, but I think we need input from those > > that have taken the time to implement their own oom notifier to see if > > they agree. In the past, they would only be called if reclaim has > > completely failed; now, they can be called in low memory situations when > > reclaim has had very little chance to be successful. Getting an ack from > > them would be helpful. > > I will make sure to put them on the CC and mention this in the changelog > when I post this next time. I personally think that this shouldn't make > much difference in the real life because GFP_NOFS only loads are rare GFP_NOFS only loads are rare. But some GFP_KERNEL load which got TIF_MEMDIE might be waiting for GFP_NOFS or GFP_NOIO loads to make progress. I think we are not ready to handle situations where out_of_memory() is called again after current thread got TIF_MEMDIE due to __GFP_NOFAIL allocation request when we ran out of memory reserves. We should not assume that the victim target thread does not have TIF_MEMDIE yet. I think we can handle it by making mark_oom_victim() return a bool and return via shortcut only if mark_oom_victim() successfully set TIF_MEMDIE. Though I don't like the shortcut approach that lacks a guaranteed unlocking mechanism. > and we should rather help by releasing memory when it is available > rather than rely on something else to do it for us. Waiting for Godot is > never a good strategy. > > > I also think we have discussed this before, but I think the oom notifier > > handling should be in done in the page allocator proper, i.e. in > > __alloc_pages_may_oom(). We can leave out_of_memory() for a clear defined > > purpose: to kill a process when all reclaim has failed. > > I vaguely remember there was some issue with that the last time we have > discussed that. It was the duplication from the page fault and allocator > paths AFAIR. Nothing that cannot be handled though but the OOM notifier > API is just too ugly to spread outside OOM proper I guess. Why we cannot > move those users to use proper shrinkers interface (after it gets > extended by a priority of some sort and release some objects only after > we are really in troubles)? Something for a separate discussion, > though... Calling oom notifiers from SysRq-f is what we want? -- 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>