On Mon, Aug 19, 2024 at 6:10 PM Barry Song <21cnbao@xxxxxxxxx> wrote: > > On Mon, Aug 19, 2024 at 9:46 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote: > > > > On Mon, Aug 19, 2024 at 5:39 PM Barry Song <21cnbao@xxxxxxxxx> wrote: > > > > > > On Mon, Aug 19, 2024 at 9:25 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote: > > > > > > > > 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. > > > > From the user's perspective, there's no noticeable difference between > > > > a livelock, soft lockup, or hard lockup. > > > > > > This is certainly different. A lockup occurs when tasks can't be scheduled, > > > causing the entire system to stop functioning. > > > > When a livelock occurs, your only options are to migrate your > > applications to other servers or reboot the system—there’s no other > > resolution (except for using oomd, which is difficult for users > > without cgroup2 or swap). > > > > So, there's effectively no difference. > > Could you express your options more clearly? I am guessing two > possibilities? > 1. entirely drop __GFP_NOFAIL and require all users who are > using __GFP_NOFAIL to add error handlers instead? When the system is unstable—such as after reaching the maximum retries without successfully allocating pages—simply failing the operation might be the better option. > > 2. no matter if it is an unsupported case, such as, GFP_ATOMIC| > __GFP_NOFAIL, we always loop till a soft or hard lockup? -- Regards Yafang
