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From: Phil Sutter <phil@nwl.cc>
To: Eric Dumazet <edumazet@google.com>
Cc: David Ahern <dsahern@gmail.com>,
	Stephen Hemminger <stephen@networkplumber.org>,
	netdev <netdev@vger.kernel.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Hangbin Liu <liuhangbin@gmail.com>
Subject: Re: [PATCH iproute2] lib/libnetlink: ensure a minimum of 32KB for the buffer used in rtnl_recvmsg()
Date: Wed, 13 Feb 2019 18:46:22 +0100	[thread overview]
Message-ID: <20190213174622.GD19329@orbyte.nwl.cc> (raw)
In-Reply-To: <20190213015841.140383-1-edumazet@google.com>

Hi Eric,

On Tue, Feb 12, 2019 at 05:58:41PM -0800, Eric Dumazet 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.

Wouldn't it be better if the kernel recognized MSG_TRUNC and allocated a
buffer large enough to hold the full message in that case? I have no
idea how hard that would be to implement, but calling recvmsg() with
MSG_TRUNC set and not getting the full message length in return is not
quite what one expects after reading recvmsg(2).

Cheers, Phil

  parent reply	other threads:[~2019-02-13 17:46 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-13  1:58 [PATCH iproute2] lib/libnetlink: ensure a minimum of 32KB for the buffer used in rtnl_recvmsg() Eric Dumazet
2019-02-13  2:04 ` David Ahern
2019-02-13  2:08   ` Eric Dumazet
2019-02-13  6:20     ` Hangbin Liu
2019-02-14 13:51       ` Michal Kubecek
2019-02-14 13:49   ` Michal Kubecek
2019-02-14 17:34     ` David Ahern
2019-02-14 17:47       ` Phil Sutter
2023-05-29 12:29   ` Gal Pressman
2023-05-31 21:51     ` Stephen Hemminger
2023-06-04 13:33       ` Gal Pressman
2023-06-04 16:03         ` David Ahern
2023-06-05  7:24           ` Gal Pressman
2019-02-13 17:46 ` Phil Sutter [this message]
2019-02-13 17:58   ` Eric Dumazet
2019-02-13 21:57 ` Stephen Hemminger
2019-02-13 21:59   ` Eric Dumazet

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