On Wed, Jul 6, 2022 at 5:25 PM Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote: > > On Thu, Jul 07, 2022 at 12:07:21AM +0000, Shakeel Butt wrote: > > On Wed, Jul 06, 2022 at 03:58:47PM +0000, Yafang Shao wrote: > > > GFP_ATOMIC doesn't cooperate well with memcg pressure so far, especially > > > if we allocate too much GFP_ATOMIC memory. For example, when we set the > > > memcg limit to limit a non-preallocated bpf memory, the GFP_ATOMIC can > > > easily break the memcg limit by force charge. So it is very dangerous to > > > use GFP_ATOMIC in non-preallocated case. One way to make it safe is to > > > remove __GFP_HIGH from GFP_ATOMIC, IOW, use (__GFP_ATOMIC | > > > __GFP_KSWAPD_RECLAIM) instead, then it will be limited if we allocate > > > too much memory. > > > > Please use GFP_NOWAIT instead of (__GFP_ATOMIC | __GFP_KSWAPD_RECLAIM). > > There is already a plan to completely remove __GFP_ATOMIC and mm-tree > > already have a patch for that. > > Oh, I didn't know this, thanks for heads up! > I agree that GFP_NOWAIT is the best choice then. > > Btw, we probably shouldn't even add GFP_NOWAIT if the allocation is performed > from the bpf syscall context. Why would we fail to pre-allocate a map if > we can easily go into the reclaim? But probably better to leave it for > a separate change. The places affected by this patch are in atomic context. Prealloc path from syscall is using GFP_USER.
