Re: [RFC PATCH] mm: net: disable kswapd for high-order network buffer allocation

[Barry Song <21cnbao@gmail.com>]

> >
> > >
> > > I think you are missing something to control how much memory  can be
> > > pushed on each TCP socket ?
> > >
> > > What is tcp_wmem on your phones ? What about tcp_mem ?
> > >
> > > Have you looked at /proc/sys/net/ipv4/tcp_notsent_lowat
> >
> > # cat /proc/sys/net/ipv4/tcp_wmem
> > 524288  1048576 6710886
>
> Ouch. That is insane tcp_wmem[0] .
>
> Please stick to 4096, or risk OOM of various sorts.
>
> >
> > # cat /proc/sys/net/ipv4/tcp_notsent_lowat
> > 4294967295
> >
> > Any thoughts on these settings?
>
> Please look at
> https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
>
> tcp_notsent_lowat - UNSIGNED INTEGER
> A TCP socket can control the amount of unsent bytes in its write queue,
> thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
> reports POLLOUT events if the amount of unsent bytes is below a per
> socket value, and if the write queue is not full. sendmsg() will
> also not add new buffers if the limit is hit.
>
> This global variable controls the amount of unsent data for
> sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
> to the global variable has immediate effect.
>
>
> Setting this sysctl to 2MB can effectively reduce the amount of memory
> in TCP write queues by 66 %,
> or allow you to increase tcp_wmem[2] so that only flows needing big
> BDP can get it.

We obtained these settings from our hardware vendors.

It might be worth exploring these settings further, but I can’t quite see
their connection to high-order allocations, since high-order allocations are
kernel macros.

#define SKB_FRAG_PAGE_ORDER     get_order(32768)
#define PAGE_FRAG_CACHE_MAX_SIZE        __ALIGN_MASK(32768, ~PAGE_MASK)
#define PAGE_FRAG_CACHE_MAX_ORDER       get_order(PAGE_FRAG_CACHE_MAX_SIZE)

Is there anything I’m missing?

Thanks
Barry