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authorIzik Eidus <ieidus@redhat.com>2009-09-21 20:01:51 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-22 10:17:31 -0400
commit828502d30073036a486d96b1fe051e0f08b6df83 (patch)
tree61b728cbeb88c1a2c522307dff6264e8d0b1d8f1 /mm/mmu_notifier.c
parent451ea25da71590361c71bf3044c55b870a887d53 (diff)
ksm: add mmu_notifier set_pte_at_notify()
KSM is a linux driver that allows dynamicly sharing identical memory pages between one or more processes. Unlike tradtional page sharing that is made at the allocation of the memory, ksm do it dynamicly after the memory was created. Memory is periodically scanned; identical pages are identified and merged. The sharing is made in a transparent way to the processes that use it. Ksm is highly important for hypervisors (kvm), where in production enviorments there might be many copys of the same data data among the host memory. This kind of data can be: similar kernels, librarys, cache, and so on. Even that ksm was wrote for kvm, any userspace application that want to use it to share its data can try it. Ksm may be useful for any application that might have similar (page aligment) data strctures among the memory, ksm will find this data merge it to one copy, and even if it will be changed and thereforew copy on writed, ksm will merge it again as soon as it will be identical again. Another reason to consider using ksm is the fact that it might simplify alot the userspace code of application that want to use shared private data, instead that the application will mange shared area, ksm will do this for the application, and even write to this data will be allowed without any synchinization acts from the application. Ksm was designed to be a loadable module that doesn't change the VM code of linux. This patch: The set_pte_at_notify() macro allows setting a pte in the shadow page table directly, instead of flushing the shadow page table entry and then getting vmexit to set it. It uses a new change_pte() callback to do so. set_pte_at_notify() is an optimization for kvm, and other users of mmu_notifiers, for COW pages. It is useful for kvm when ksm is used, because it allows kvm not to have to receive vmexit and only then map the ksm page into the shadow page table, but instead map it directly at the same time as Linux maps the page into the host page table. Users of mmu_notifiers who don't implement new mmu_notifier_change_pte() callback will just receive the mmu_notifier_invalidate_page() callback. Signed-off-by: Izik Eidus <ieidus@redhat.com> Signed-off-by: Chris Wright <chrisw@redhat.com> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Avi Kivity <avi@redhat.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mmu_notifier.c')
-rw-r--r--mm/mmu_notifier.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 5f4ef0250bee..7e33f2cb3c77 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -99,6 +99,26 @@ int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
99 return young; 99 return young;
100} 100}
101 101
102void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
103 pte_t pte)
104{
105 struct mmu_notifier *mn;
106 struct hlist_node *n;
107
108 rcu_read_lock();
109 hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
110 if (mn->ops->change_pte)
111 mn->ops->change_pte(mn, mm, address, pte);
112 /*
113 * Some drivers don't have change_pte,
114 * so we must call invalidate_page in that case.
115 */
116 else if (mn->ops->invalidate_page)
117 mn->ops->invalidate_page(mn, mm, address);
118 }
119 rcu_read_unlock();
120}
121
102void __mmu_notifier_invalidate_page(struct mm_struct *mm, 122void __mmu_notifier_invalidate_page(struct mm_struct *mm,
103 unsigned long address) 123 unsigned long address)
104{ 124{