On 12/06/2016 11:38 AM, Tetsuo Handa wrote: >> >> So we are somewhere in the middle between pre-mature and pointless >> system disruption (GFP_NOFS with a lots of metadata or lowmem request) >> where the OOM killer even might not help and potential lockup which is >> inevitable with the current design. Dunno about you but I would rather >> go with the first option. To be honest I really fail to understand your >> line of argumentation. We have this >> do { >> cond_resched(); >> } while (!(page = alloc_page(GFP_NOFS))); >> vs. >> page = alloc_page(GFP_NOFS | __GFP_NOFAIL); >> >> the first one doesn't invoke OOM killer while the later does. This >> discrepancy just cannot make any sense... The same is true for >> >> alloc_page(GFP_DMA) vs alloc_page(GFP_DMA|__GFP_NOFAIL) >> >> Now we can discuss whether it is a _good_ idea to not invoke OOM killer >> for those exceptions but whatever we do __GFP_NOFAIL is not a way to >> give such a subtle side effect. Or do you disagree even with that? > > "[PATCH 1/2] mm: consolidate GFP_NOFAIL checks in the allocator slowpath" > silently changes __GFP_NOFAIL vs. __GFP_NORETRY priority.
I guess that wasn't intended? > Currently, __GFP_NORETRY is stronger than __GFP_NOFAIL; __GFP_NOFAIL > allocation requests fail without invoking the OOM killer when both > __GFP_NORETRY and __GFP_NOFAIL are given. > > With [PATCH 1/2], __GFP_NOFAIL becomes stronger than __GFP_NORETRY; > __GFP_NOFAIL allocation requests will loop forever without invoking > the OOM killer when both __GFP_NORETRY and __GFP_NOFAIL are given. Does such combination of flag make sense? Should we warn about it, or even silently remove __GFP_NORETRY in such case? > Those callers which prefer lockup over panic can specify both > __GFP_NORETRY and __GFP_NOFAIL. What lockup exactly, if __GFP_NORETRY did lead to fail?