On Mon, Aug 19, 2024 at 3:50 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Sun 18-08-24 10:55:09, Yafang Shao wrote: > > On Sat, Aug 17, 2024 at 2:25 PM Barry Song <21cnbao@xxxxxxxxx> wrote: > > > > > > From: Barry Song <v-songbaohua@xxxxxxxx> > > > > > > When users allocate memory with the __GFP_NOFAIL flag, they might > > > incorrectly use it alongside GFP_ATOMIC, GFP_NOWAIT, etc. This kind of > > > non-blockable __GFP_NOFAIL is not supported and is pointless. If we > > > attempt and still fail to allocate memory for these users, we have two > > > choices: > > > > > > 1. We could busy-loop and hope that some other direct reclamation or > > > kswapd rescues the current process. However, this is unreliable > > > and could ultimately lead to hard or soft lockups, > > > > That can occur even if we set both __GFP_NOFAIL and > > __GFP_DIRECT_RECLAIM, right? > > No, it cannot! With __GFP_DIRECT_RECLAIM the allocator might take a long > time to satisfy the allocation but it will reclaim to get the memory, it > will sleep if necessary and it will will trigger OOM killer if there is > no other option. __GFP_DIRECT_RECLAIM is a completely different story > than without it which means _no_sleeping_ is allowed and therefore only > a busy loop waiting for the allocation to proceed is allowed. That could be a livelock.
