lkml.org 
[lkml]   [2013]   [Mar]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/7] ksm: treat unstable nid like in stable tree
On Wed, 6 Mar 2013, Ric Mason wrote:
[ I've deleted the context because that was about the unstable tree,
and here you have moved to asking about a case in the stable tree. ]
>
> For the case of a ksm page is migrated to a different NUMA node and migrate
> its stable node to the right tree and collide with an existing stable node.
> get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid) can capture nothing

That's not so: as I've pointed out before, ksm_migrate_page() updates
stable_node->kpfn for the new page on the new NUMA node; but it cannot
(get the right locking to) move the stable_node to its new tree at that time.

It's moved out once ksmd notices that it's in the wrong NUMA node tree -
perhaps when one its rmap_items reaches the head of cmp_and_merge_page(),
or perhaps here in stable_tree_search() when it matches another page
coming in to cmp_and_merge_page().

You may be concentrating on the case when that "another page" is a ksm
page migrated from a different NUMA node; and overlooking the case of
when the matching ksm page in this stable tree has itself been migrated.

> since stable_node is the node in the right stable tree, nothing happen to it
> before this check. Did you intend to check get_kpfn_nid(page_node->kpfn) !=
> NUMA(page_node->nid) ?

Certainly not: page_node is usually NULL. But I could have checked
get_kpfn_nid(stable_node->kpfn) != nid: I was duplicating the test
from cmp_and_merge_page(), but here we do have local variable nid.

Hugh


\
 
 \ /
  Last update: 2013-03-06 06:43    [W:0.088 / U:1.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site