On Wed, Jun 29, 2022 at 03:48:29PM +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. > > We introduced BPF_F_NO_PREALLOC is because full map pre-allocation is > too memory expensive for some cases. That means removing __GFP_HIGH > doesn't break the rule of BPF_F_NO_PREALLOC, but has the same goal with > it-avoiding issues caused by too much memory. So let's remove it. > > __GFP_KSWAPD_RECLAIM doesn't cooperate well with memcg pressure neither > currently. But the memcg code can be improved to make > __GFP_KSWAPD_RECLAIM work well under memcg pressure. > > It also fixes a typo in the comment. > > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> > Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx> I agree, it makes total sense to me. Bpf allocations are not high priority and should not be enforced both on memcg and page allocator levels. Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx> Thanks, Yafang!
