On Sat, Jul 2, 2022 at 12:14 PM Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote: > > On Thu, Jun 30, 2022 at 11:47:00PM +0200, Daniel Borkmann wrote: > > Hi Yafang, > > > > On 6/29/22 5:48 PM, 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. > > > > Ok, but could you also explain in commit desc why it's a specific problem > > to BPF hashtab? > > > > Afaik, there is plenty of other code using GFP_ATOMIC | __GFP_NOWARN outside > > of BPF e.g. under net/, so it's a generic memcg problem? > > I'd be careful here and not change it all together. > > __GFP_NOWARN might be used to suppress warnings which otherwise would be too > verbose and disruptive (especially if we talk about /net allocations in > conjunction with netconsole) and might not mean a low/lower priority. > > > Why are lpm trie and local storage map for BPF not affected (at least I don't > > see them covered in the patch)? > > Yes, it would be nice to fix this consistently over the bpf code. > Yafang, would you mind to fix it too? > I will fix it. -- Regards Yafang
