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From: Lee Schermerhorn <>
To: Andi Kleen <>
Cc: David Rientjes <>, Paul Jackson <>,,,
Subject: Re: [patch -mm 2/2] mempolicy: use default_policy mode instead of MPOL_DEFAULT
Date: Mon, 10 Mar 2008 09:48:01 -0400	[thread overview]
Message-ID: <1205156881.5579.5.camel@localhost> (raw)
In-Reply-To: <>

On Sun, 2008-03-09 at 00:19 +0100, Andi Kleen wrote:
> > Using MPOL_DEFAULT purely for falling back to the task or system-wide 
> > policy, however, seems confusing.  The semantics seem to indicate that 
> > MPOL_DEFAULT represents the system-wide default policy without any 
> > preferred node or set of nodes to bind or interleave.  So if a VMA has a 
> > policy of MPOL_DEFAULT then, to me, it seems like that indicates the 
> > absence of a specific policy, not a mandate to fallback to the task 
> > policy.
> I designed MPOL_DEFAULT on vma originally to be a fallback to the task policy.
> Absence of specific policy would be MPOL_PREFERRED with -1 node.

Not sure what you mean here, Andi.   

"MPOL_PREFERRED with -1 node" == "local allocation", right?  

Whereas, in the task mempolicy or vma policy or shared policy, the lack
of a specific policy--i.e., a null mempolicy pointer, or no policy at
that offset in a shared policy rbtree--means fall back to surrounding
context, right?  As far back as I've looked, mempolicy.c implemented
MPOL_DEFAULT, passed to set_mempolicy() or mbind(), by deleting the
target policy, resulting in "fall back".  

The only place that MPOL_DEFAULT actually occurs in a struct mempolicy
is in the system default policy.  I think we can simplify the code and
documentation--not have to explain the context dependent meaning of
MPOL_DEFAULT--by making it simply an API request to remove the target
policy and establish "default behavior" for that context--i.e.,

> -Andi

  reply	other threads:[~2008-03-10 13:48 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-08  1:24 [patch -mm 1/2] mempolicy: disallow static or relative flags for local preferred mode David Rientjes
2008-03-08  1:24 ` [patch -mm 2/2] mempolicy: use default_policy mode instead of MPOL_DEFAULT David Rientjes
2008-03-08  1:28   ` Paul Jackson
2008-03-08  1:33     ` David Rientjes
2008-03-08  1:35       ` Paul Jackson
2008-03-08  1:59         ` Christoph Lameter
2008-03-08  2:14           ` David Rientjes
2008-03-08 19:13       ` Lee Schermerhorn
2008-03-08 22:20         ` David Rientjes
2008-03-08 23:19           ` Andi Kleen
2008-03-10 13:48             ` Lee Schermerhorn [this message]
2008-03-10 19:09 ` [patch -mm 1/2] mempolicy: disallow static or relative flags for local preferred mode Andrew Morton

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