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From: Menglong Dong <menglong8.dong@gmail.com>
To: jmaloy@redhat.com
Cc: ying.xue@windriver.com, David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	etdev@vger.kernel.org, tipc-discussion@lists.sourceforge.net,
	LKML <linux-kernel@vger.kernel.org>
Subject: The value of FB_MTU eats two pages
Date: Tue, 1 Jun 2021 22:18:29 +0800	[thread overview]
Message-ID: <CADxym3baupJJ7Q9otxtoQ-DH5e-J2isg-LZj2CsOqRPo70AL4A@mail.gmail.com> (raw)

Hello!

I have a question about the value of FB_MTU in tipc, how does the '3744' form?
I notice that it is used in 'tipc_msg_build()' when memory allocation
fails, and it
tries to fall back to a smaller MTU to avoid unnecessary sending failures.

However, the size of the data allocated will be more than 4096 when FB_MTU
is 3744. I did a rough calculation, the size of data will more than 4200:

(FB_MTU + TIPCHDR + BUF_HEADROOM + sizeof(struct skb_shared_info))

Therefore, 8192 will be allocated from slab, and about 4000 of it will
not be used.

FB_MTU is used for low memory, and I think eating two pages will make it worse.
Do I miss something?

Thanks!
Menglong Dong

             reply	other threads:[~2021-06-01 14:18 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-01 14:18 Menglong Dong [this message]
2021-06-02 19:50 ` Jon Maloy
2021-06-03  2:26   ` Menglong Dong
2021-06-03 13:08     ` Jon Maloy
2021-06-03 14:54       ` Menglong Dong

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