On Tue, Sep 20, 2016 at 05:12:16PM +0200, Vlastimil Babka wrote:

[CC += linux-api@vger.kernel.org]

    Since this is a kernel-user-space API change, please CC linux-api@. The
kernel source file Documentation/SubmitChecklist notes that all Linux kernel
patches that change userspace interfaces should be CCed to
linux-api@vger.kernel.org, so that the various parties who are interested in
API changes are informed. For further information, see
https://www.kernel.org/doc/man-pages/linux-api-ml.html

I think man page should document the change? Also I noticed that MPOL_NUMA
itself is missing in the man page...

On 09/18/2016 01:29 PM, Piotr Kwapulinski wrote:

quoted

The MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES flags are irrelevant
when setting them for MPOL_LOCAL NUMA memory policy via set_mempolicy.
Return the "invalid argument" from set_mempolicy whenever
any of these flags is passed along with MPOL_LOCAL.
It is consistent with MPOL_PREFERRED passed with empty nodemask.
It also slightly shortens the execution time in paths where these flags
are used e.g. when trying to rebind the NUMA nodes for changes in
cgroups cpuset mems (mpol_rebind_preferred()) or when just printing
the mempolicy structure (/proc/PID/numa_maps).

Hmm not sure I understand. How does change in mpol_new() affect
mpol_rebind_preferred()?

When MPOL_LOCAL is passed to set_mempolicy along with empty nodemask 
it is transformed into MPOL_PREFERRED (inside mpol_new()).
Unlike MPOL_PREFERRED the MPOL_LOCAL may be set along with 
MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES flag (inconsistency).
Later on when the set of allowed NUMA nodes is changed by cgroups 
cpuset.mems the mpol_rebind_preferred() is called. Because one of
the flags is set the unnecessary code is executed. The same is for
mpol_to_str().

Vlastimil

quoted

Isolated tests done.

Signed-off-by: Piotr Kwapulinski <redacted>
---
 mm/mempolicy.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 2da72a5..27b07d1 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -276,7 +276,9 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
 				return ERR_PTR(-EINVAL);
 		}
 	} else if (mode == MPOL_LOCAL) {
-		if (!nodes_empty(*nodes))
+		if (!nodes_empty(*nodes) ||
+		    (flags & MPOL_F_STATIC_NODES) ||
+		    (flags & MPOL_F_RELATIVE_NODES))
 			return ERR_PTR(-EINVAL);
 		mode = MPOL_PREFERRED;
 	} else if (nodes_empty(*nodes))

--
Piotr Kwapulinski

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