linux-kernel - strange PAGE_ALLOC_COSTLY_ORDER usage in xgbe_map_rx

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Message-ID: <20170531160422.GW27783@dhcp22.suse.cz>
Date:   Wed, 31 May 2017 18:04:23 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: strange PAGE_ALLOC_COSTLY_ORDER usage in xgbe_map_rx_buffer

Hi Tom,
I have stumbled over the following construct in xgbe_map_rx_buffer
	order = max_t(int, PAGE_ALLOC_COSTLY_ORDER - 1, 0);
which looks quite suspicious. Why does it PAGE_ALLOC_COSTLY_ORDER - 1?
And why do you depend on PAGE_ALLOC_COSTLY_ORDER at all?

Thanks!
-- 
Michal Hocko
SUSE Labs