Messages in this thread | | | Subject | Re: Regression: Re: [patch -mm 2/4] mempolicy: create mempolicy_operations structure | From | Lee Schermerhorn <> | Date | Sat, 08 Mar 2008 13:49:31 -0500 |
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On Fri, 2008-03-07 at 13:48 -0800, David Rientjes wrote: > On Fri, 7 Mar 2008, Lee Schermerhorn wrote: > > > It also appears that the patch series listed above required a non-empty > > nodemask with MPOL_DEFAULT. However, I didn't test that. With this > > patch, MPOL_DEFAULT effectively ignores the nodemask--empty or not. > > This is a change in behavior that I have argued against, but the > > regression tests don't test this, so I'm not going to attempt to address > > it with this patch. > > > > Excuse me, but there was significant discussion about this on LKML and I > eventually did force MPOL_DEFAULT to require a non-empty nodemask > specifically because of your demand that it should. It didn't originally > require this in my patchset, and now you're removing the exact same > requirement that you demanded. > > You said on February 13: > > 1) we've discussed the issue of returning EINVAL for non-empty > nodemasks with MPOL_DEFAULT. By removing this restriction, we run > the risk of breaking applications if we should ever want to define > a semantic to non-empty node mask for MPOL_DEFAULT. > > If you want to remove this requirement now (please get agreement from > Paul) and are sure of your position, you'll at least need an update to > Documentation/vm/numa-memory-policy.txt.
Excuse me. I thought that the discussion--my position, anyway--was about preserving existing behavior for MPOL_DEFAULT which is to require an EMPTY [or NULL--same effect] nodemask. Not a NON-EMPTY one. See: http://www.kernel.org/doc/man-pages/online/pages/man2/set_mempolicy.2.html It does appear that your patches now require a non-empty nodemask. This was intentional?
Is it, then, the case that our disagreement was based on the fact that you thought I was advocating a non-empty nodemask with MPOL_DEFAULT? No wonder you said it didn't make sense.
Since we can't seem to understand each other with ~English prose, I've attached a little test program that demonstrates the behavior that I expect. This is not to belabor the point; just an attempt to establish understanding.
Note: in the subject patch, I didn't enforce this behavior because your patch didn't [it enforced just the opposite], and I've pretty much given up. Although I prefer current behavior [before your series], if we change it, we will need to change the man pages to remove the error condition for non-empty nodemasks with MPOL_DEFAULT.
Later, Lee
/* * test error returns for set_mempolicy(MPOL_DEFAULT, nodemask, maxnodes) for * null, empty and non-empty nodemasks. * * requires libnuma */ #include <sys/types.h>
#include <errno.h> #include <numaif.h> #include <numa.h> #include <stdarg.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <unistd.h>
void results(int ret, int ierr, int expected) { if (ret) { printf("\tResults: %s [%d]\n", strerror(ierr), ierr); } else { printf("\tResults: No Error [0]\n"); } printf("\tExpected: %s [%d]\n", expected ? strerror(expected) : "No Error", expected); }
int main(int argc, char *argv[]) { unsigned long nodemask; /* hack: single long word mask */ int maxnodes = 4; /* arbitrary max <= 8 * sizeof(nodemask) */ int ret;
printf("\n1: testing set_mempolicy(MPOL_DEFAULT, ...) with NULL nodemask:\n"); ret = set_mempolicy(MPOL_DEFAULT, NULL, maxnodes); results(ret, errno, 0); /* expect success */
printf("\n2: testing set_mempolicy(MPOL_DEFAULT, ...) with non-NULL, " "but empty, nodemask:\n"); nodemask = 0UL; ret = set_mempolicy(MPOL_DEFAULT, &nodemask, maxnodes); results(ret, errno, 0); /* expect success */
printf("\n2: testing set_mempolicy(MPOL_DEFAULT, ...) with non-NULL, " "non-empty nodemask:\n"); nodemask = 1UL; ret = set_mempolicy(MPOL_DEFAULT, &nodemask, maxnodes); results(ret, errno, EINVAL); /* expect EINVAL */
}
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