Hi Hugh,
On 02/23/2013 05:03 AM, Hugh Dickins wrote:
On Fri, 22 Feb 2013, Ric Mason wrote:
On 02/21/2013 04:20 PM, Hugh Dickins wrote:
An inconsistency emerged in reviewing the NUMA node changes to KSM:
when meeting a page from the wrong NUMA node in a stable tree, we say
that it's okay for comparisons, but not as a leaf for merging; whereas
when meeting a page from the wrong NUMA node in an unstable tree, we
bail out immediately.
IIUC
- ksm page from the wrong NUMA node will be add to current node's stable tree
Please forgive my late response.
That should never happen (and when I was checking with a WARN_ON it did
not happen). What can happen is that a node already in a stable tree
has its page migrated away to another NUMA node.
- normal page from the wrong NUMA node will be merged to current node's
stable tree <- where I miss here? I didn't see any special handling in
function stable_tree_search for this case.
nid = get_kpfn_nid(page_to_pfn(page));
root = root_stable_tree + nid;
to choose the right tree for the page, and
if (get_kpfn_nid(stable_node->kpfn) !=
NUMA(stable_node->nid)) {
put_page(tree_page);
goto replace;
}
to make sure that we don't latch on to a node whose page got migrated away.
I think the ksm implementation for num awareness is buggy.
For page migratyion stuff, new page is allocated from node *which page
is migrated to*.
- when meeting a page from the wrong NUMA node in an unstable tree
get_kpfn_nid(page_to_pfn(page)) *==* page_to_nid(tree_page)
How can say it's okay for comparisons, but not as a leaf for merging?
- when meeting a page from the wrong NUMA node in an stable tree
- meeting a normal page
- meeting a page which is ksm page before migration
get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid) can't
capture them since stable_node is for tree page in current stable tree.
They are always equal.
- normal page from the wrong NUMA node will compare but not as a leaf for
merging after the patch
I don't understand you there, but hope my remarks above resolve it.
Hugh
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