netdev - RE: [net-next 13/15] ice: Use bitfields where possible

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Message-ID: <dfd0b9bf9180413788b04984fd007b07@AcuMS.aculab.com>
Date:   Tue, 7 May 2019 10:47:57 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jeff Kirsher' <jeffrey.t.kirsher@...el.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     Jesse Brandeburg <jesse.brandeburg@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "sassmann@...hat.com" <sassmann@...hat.com>,
        Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>,
        Andrew Bowers <andrewx.bowers@...el.com>
Subject: RE: [net-next 13/15] ice: Use bitfields where possible

From: Jeff Kirsher
> Sent: 05 May 2019 00:49
> The driver was converted to not use bool, but it was
> neglected that the bools should have been converted to bit fields
> as bit fields in software structures are ok, as long as they
> use the correct kinds of unsigned types. This avoids
> wasting lots of storage space to store single bit values.
> 
> One of the change hunks moves a variable lport out of
> a group of "combinable" bit fields because all bits of
> the u8 lport are valid and the variable can be packed in the
> struct in struct holes.

How many copies of this structure are there?
You may find that the code size increases more than the date size reduction.
Also, unless the data size goes below a malloc threshold is saves
no memory at all.

	David

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