netdev - Re: [PATCH iproute2] lib/libnetlink: ensure a minimum of 32KB for the buffer used in rtnl

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Date:   Wed, 13 Feb 2019 13:59:01 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     David Ahern <dsahern@...il.com>, netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Hangbin Liu <liuhangbin@...il.com>, Phil Sutter <phil@....cc>
Subject: Re: [PATCH iproute2] lib/libnetlink: ensure a minimum of 32KB for the
 buffer used in rtnl_recvmsg()

On Wed, Feb 13, 2019 at 1:57 PM Stephen Hemminger
<stephen@...workplumber.org> wrote:
>
> On Tue, 12 Feb 2019 17:58:41 -0800
> Eric Dumazet <edumazet@...gle.com> wrote:
>
> > In the past, we tried to increase the buffer size up to 32 KB in order
> > to reduce number of syscalls per dump.
> >
> > Commit 2d34851cd341 ("lib/libnetlink: re malloc buff if size is not enough")
> > brought the size back to 4KB because the kernel can not know the application
> > is ready to receive bigger requests.
> >
> > See kernel commits 9063e21fb026 ("netlink: autosize skb lengthes") and
> > d35c99ff77ec ("netlink: do not enter direct reclaim from netlink_dump()")
> > for more details.
> >
> > Fixes: 2d34851cd341 ("lib/libnetlink: re malloc buff if size is not enough")
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: Hangbin Liu <liuhangbin@...il.com>
> > Cc: Phil Sutter <phil@....cc>
>
> Applied, although maybe we should bump it to 64K or bigger?

Note the kernel does not yet try 64KB allocations, so I do not see an
urgent need for that :)