Re: [PATCH bpf-next v3 1/2] bpf: Make non-preallocated allocation low priority

[Shakeel Butt <shakeelb@google.com>]

On Sat, Jul 9, 2022 at 8:45 AM Yafang Shao <laoar.shao@gmail.com> 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. There's a plan to completely remove __GFP_ATOMIC in the
> mm side[1], so let's use GFP_NOWAIT instead.
>
> 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.
>
> This fix can also apply to other run-time allocations, for example, the
> allocation in lpm trie, local storage and devmap. So let fix it
> consistently over the bpf code
>
> It also fixes a typo in the comment.
>
> [1]. https://lore.kernel.org/linux-mm/163712397076.13692.4727608274002939094@noble.neil.brown.name/
>
> Cc: Roman Gushchin <roman.gushchin@linux.dev>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: NeilBrown <neilb@suse.de>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>