After the previous commit is finally safe to revert commit dbae2b0628
("net: skb: introduce and use a single page frag cache"): do it here.
The intended goal of such change was to counter a performance regression
introduced by commit 3226b158e6 ("net: avoid 32 x truesize
under-estimation for tiny skbs").
Unfortunately, the blamed commit introduces another regression for the
virtio_net driver. Such a driver calls napi_alloc_skb() with a tiny
size, so that the whole head frag could fit a 512-byte block.
The single page frag cache uses a 1K fragment for such allocation, and
the additional overhead, under small UDP packets flood, makes the page
allocator a bottleneck.
Thanks to commit bf9f1baa27 ("net: add dedicated kmem_cache for
typical/small skb->head"), this revert does not re-introduce the
original regression. Actually, in the relevant test on top of this
revert, I measure a small but noticeable positive delta, just above
noise level.
The revert itself required some additional mangling due to recent updates
in the affected code.
Suggested-by: Eric Dumazet <edumazet@google.com>
Fixes: dbae2b0628 ("net: skb: introduce and use a single page frag cache")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
6bc7e4eb04