linux-kernel - Re: [patch 3/4] mempolicy: add MPOL_F_STATIC

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Message-ID: <alpine.DEB.1.00.0802141135110.17096@chino.kir.corp.google.com>
Date:	Thu, 14 Feb 2008 11:40:33 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Paul Jackson <pj@....com>
cc:	akpm@...ux-foundation.org, clameter@....com,
	Lee.Schermerhorn@...com, ak@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [patch 3/4] mempolicy: add MPOL_F_STATIC_NODES flag

On Thu, 14 Feb 2008, Paul Jackson wrote:

> If we ever call mpol_rebind_policy() with an MPOL_PREFERRED|MPOL_F_STATIC_NODES
> policy when the preferred_node doesn't happen to be in the current cpuset,
> then would the following lines loose the preferred node setting, such that
> it didn't get applied again correctly if that node came back into our allowed
> cpuset ?
> 
>         case MPOL_PREFERRED:
>                 if (!remap && !node_isset(pol->v.preferred_node, *newmask))
>                         pol->v.preferred_node = -1;
> 

That's already been corrected as a result of a discussion between Lee and 
myself (please see the incremental patch that I sent you privately when I 
sent the patchset along).

> Should the mpol_equal() algorithm change, in the case of either
> MPOL_F_RELATIVE_NODES or MPOL_F_STATIC_NODES, to checking
> user_nodemask equality, -instead- of the "switch(mode)"
> mode specific tests?
> 

That's a good question.

We'll need to decide whether mpol_equal() is determining the equality of 
the currently effected mempolicy (whereas policy->user_nodemask is 
irrelevant) or the whole intended mempolicy overall.

I didn't originally modify mpol_equal() because I preferred the former.  
Is there a compelling case for the latter where mpol_equal() is used in 
the tree that would require this change?

> Could we have mpol_to_str() mark policies which are
> MPOL_F_RELATIVE_NODES or MPOL_F_STATIC_NODES?  Perhaps
> by adding a suffix of "|relative" or "|static" or some
> such.
> 

I'd like to keep it in the same format as the tmpfs mount option which is 
'=relative' and '=static'.

		David
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