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mm/ksm.c is doing an unneeded _notify in write_protect_page.

PATCH In review Robin Holt 2 participants 2 messages Mar 11, 2010

Subsystems (2)
Memory management Memory management - KSM (Kernel Samepage Merging)
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Robin Holt

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#0 lore raw

PATCH 1/1 mm/ksm.c is doing an unneeded _notify in write_protect_page.

ksm.c's write_protect_page implements a lockless means of verifying a page does not have any users of the page which are not accounted for via other kernel tracking means. It does this by removing the writable pte with TLB flushes, checking the page_count against the total known users, and then using set_pte_at_notify to make it a read-only entry.

An unneeded mmu_notifier callout is made in the case where the known users does not match the page_count. In that event, we are inserting the identical pte and there is no need for the set_pte_at_notify, but rather the simpler set_pte_at suffices.

To: Andrew Morton <[email protected]>

Signed-off-by Robin Holt <[email protected]>
Acked-by Izik Eidus <[email protected]>
Acked-by Andrea Arcangeli <[email protected]>
Cc Hugh Dickins <[email protected]>
Cc Chris Wright <[email protected]>
Cc [email protected]

---

 mm/ksm.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
mm/ksm.c +1 -1
Index: ksm_remove_notify/mm/ksm.c
===================================================================
@@ -751,7 +751,7 @@ static int write_protect_page(struct vm_
 		 * page
 		 */
 		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
-			set_pte_at_notify(mm, addr, ptep, entry);
+			set_pte_at(mm, addr, ptep, entry);
 			goto out_unlock;
 		}
 		entry = pte_wrprotect(entry);

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Acked-by on v1 1/1
#1 lore raw
Quoted 12 lines · Robin Holt

ksm.c's write_protect_page implements a lockless means of verifying a page does not have any users of the page which are not accounted for via other kernel tracking means. It does this by removing the writable pte with TLB flushes, checking the page_count against the total known users, and then using set_pte_at_notify to make it a read-only entry.

An unneeded mmu_notifier callout is made in the case where the known users does not match the page_count. In that event, we are inserting the identical pte and there is no need for the set_pte_at_notify, but rather the simpler set_pte_at suffices.

Quoted 5 lines

To: Andrew Morton <[email protected]>

Signed-off-by Robin Holt <[email protected]>
Acked-by Izik Eidus <[email protected]>
Acked-by Andrea Arcangeli <[email protected]>
Cc Hugh Dickins <[email protected]>
Acked-by Hugh Dickins <[email protected]>
Quoted 13 lines
Cc Chris Wright <[email protected]>
Cc [email protected]

---

 mm/ksm.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: ksm_remove_notify/mm/ksm.c
===================================================================

mm/ksm.c static int write_protect_page(struct vm_ · line 757

Quoted 8 lines
mm/ksm.c +1 -1
@@ -751,7 +751,7 @@ static int write_protect_page(struct vm_
 		 * page
 		 */
 		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
-			set_pte_at_notify(mm, addr, ptep, entry);
+			set_pte_at(mm, addr, ptep, entry);
 			goto out_unlock;
 		}
 		entry = pte_wrprotect(entry);

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>