From: Hongbo Li <herbert.tenc...@gmail.com> Date: Thu, 9 Nov 2017 16:12:27 +0800
> From: Hongbo Li <herberth...@tencent.com> > > This patch solves a memory frag issue when allocating skb. > I found this issue in a udp scenario, here is my test model: > 1. About five hundreds udp threads listen on server, > and five hundreds client threads send udp pkts to them. > Some threads send pkts in a faster speed than others. > 2. The user processes on server don't have enough ability > to receive these pkts. > > Then I got following result: > 1. Some udp sockets' recv-q reach the queue's limit, others > not because of the global rmem limit. > 2. The "free" command shows "used" memory is more than 62GB. > But cat /proc/net/sockstat shows that udp uses only 12GB. > > This will confused the user that why the system consumes so > many memory.This is caused by the memory frags in netdev layer. > __netdev_alloc_frag() allocs a page block which has 8 pages. > > Then in this scenario, most skbs are freed when the recv-q > is full, but if any skb in the same page block be queued to > other recv-q which is not full, the whole page block can't > be freed. > > So from the view of kernel, these pages are used, but from > the view of tcp/udp, only the skbs in recv-q are used. > > To avoid exhausting memory in such scenario, I add a sysctl > to make user can disable allocating skbs in page frag. > > Signed-off-by: Hongbo Li <herberth...@tencent.com> When something like page fragments don't work properly, we fix them rather then providing a way to disable them. Thank you.
