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

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On Mon, Jul 11, 2022 at 12:19 PM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>
> On Sat, Jul 9, 2022 at 8:45 AM Yafang Shao <laoar.shao@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxx/
> >
> > Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> > Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > Cc: NeilBrown <neilb@xxxxxxx>
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>

Applied to bpf-next.



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