linux-kernel - Re: [patch 3/6] mempolicy: add MPOL_F_STATIC

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Message-Id: <20080225234616.777d534c.pj@sgi.com>
Date:	Mon, 25 Feb 2008 23:46:16 -0600
From:	Paul Jackson <pj@....com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	akpm@...ux-foundation.org, clameter@....com,
	Lee.Schermerhorn@...com, ak@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [patch 3/6] mempolicy: add MPOL_F_STATIC_NODES flag

David wrote:
+static inline int mpol_store_user_nodemask(const struct mempolicy *pol)
+{
+	return !!(pol->flags & MPOL_F_STATIC_NODES);
+}

Why the double-negative?  As best as I can tell, the return value of
mpol_store_user_nodemask() is only used in conditional contexts:

    $ grep mpol_store_user_nodemask mm/mempolicy.c
    static inline int mpol_store_user_nodemask(const struct mempolicy *pol)
        if (mpol_store_user_nodemask(policy))
        if (!mpol_store_user_nodemask(a))
        if (!mpol_store_user_nodemask(pol) &&

So I see no need to waste the instructions needed (in the three copies
of this code, since it's static inline) to convert a non-zero value to
exactly the value 1.

Hmmm ... speaking of static inline ... I can knock 600 bytes (that's
IA64 bytes, so equivalent to about 300 x86 bytes) off the kernel text
size by not inlining the mm/mempolicy.c routines check_pgd_range() and
interleave_nid().  I wonder if that would be worth doing.  Perhaps
those two routines are in sufficiently tight corners that the duplicate
copies of them is needed.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.940.382.4214
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