netdev - question about size of sk_buff and skb_shared

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Message-ID: <CABGNecyP8tpBtbOPL_4fyhqnkTYEa80sHCuDrUJdm9gxihFX6w@mail.gmail.com>
Date:   Tue, 18 Apr 2017 10:34:08 -0700
From:   Code Soldier1 <codesoldier1@...il.com>
To:     netdev@...r.kernel.org
Subject: question about size of sk_buff and skb_shared_info

Hi Folks,

I am sure there is a reason for the current sizes of these structures,
However the reason is not obvious to me. So please help me understand.

Currently the size of sk_buff on an x86_64 system is 232 bytes -- Why
is that. I expected it to be a multiple of 32/64 as they are the most
common cache lines. Since the alignment calculation will align the
structure with the hw cache line, it seems like we might be wasting
space ?

skb_shared_info on the other hand is perfectly aligned with a size of 320 bytes.

Thanks,

-- 
CS1