On Mon, 27 May 2019 21:58:17 +0800 zhong jiang <zhongji...@huawei.com> wrote:
> On 2019/5/27 20:23, Vlastimil Babka wrote:
> > On 5/25/19 8:28 PM, Andrew Morton wrote:
> >> (Cc Vlastimil)
> > Oh dear, 2 years and I forgot all the details about how this works.
> >
> >> On Sat, 25 May 2019 15:07:23 +0800 zhong jiang <zhongji...@huawei.com>
> >> wrote:
> >>
> >>> We bind an different node to different vma, Unluckily,
> >>> it will bind different vma to same node by checking the
> >>> /proc/pid/numa_maps.
> >>> Commit 213980c0f23b ("mm, mempolicy: simplify rebinding mempolicies when
> >>> updating cpusets")
> >>> has introduced the issue. when we change memory policy by seting
> >>> cpuset.mems,
> >>> A process will rebind the specified policy more than one times.
> >>> if the cpuset_mems_allowed is not equal to user specified nodes. hence
> >>> the issue will trigger.
> >>> Maybe result in the out of memory which allocating memory from same node.
> > I have a hard time understanding what the problem is. Could you please
> > write it as a (pseudo) reproducer? I.e. an example of the process/admin
> > mempolicy/cpuset actions that have some wrong observed results vs the
> > correct expected result.
> Sorry, I havn't an testcase to reproduce the issue. At first, It was
> disappeared by
> my colleague to configure the xml to start an vm. To his suprise, The bind
> mempolicy
> doesn't work.
So... what do we do with this patch?
> Thanks,
> zhong jiang
> >>> --- a/mm/mempolicy.c
> >>> +++ b/mm/mempolicy.c
> >>> @@ -345,7 +345,7 @@ static void mpol_rebind_nodemask(struct mempolicy
> >>> *pol, const nodemask_t *nodes)
> >>> else {
> >>> nodes_remap(tmp, pol->v.nodes,pol->w.cpuset_mems_allowed,
> >>> *nodes);
> >>> - pol->w.cpuset_mems_allowed = tmp;
> >>> + pol->w.cpuset_mems_allowed = *nodes;
> > Looks like a mechanical error on my side when removing the code for
> > step1+step2 rebinding. Before my commit there was
> >
> > pol->w.cpuset_mems_allowed = step ? tmp : *nodes;
> >
> > Since 'step' was removed and thus 0, I should have used *nodes indeed.
> > Thanks for catching that.
Was that an ack?
> >>> }
> >>>
> >>> if (nodes_empty(tmp))
> >> hm, I'm not surprised the code broke. What the heck is going on in
> >> there? It used to have a perfunctory comment, but Vlastimil deleted
> >> it.
> > Yeah the comment was specific for the case that was being removed.
> >
> >> Could someone please propose a comment for the above code block
> >> explaining why we're doing what we do?
> > I'll have to relearn this first...
> >
> >
>
