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Message-ID: <Pine.LNX.4.64.0906081733390.7729@sister.anvils>
Date: Mon, 8 Jun 2009 17:35:36 +0100 (BST)
From: Hugh Dickins <hugh.dickins@...cali.co.uk>
To: Izik Eidus <ieidus@...hat.com>
cc: aarcange@...hat.com, akpm@...ux-foundation.org,
nickpiggin@...oo.com.au, chrisw@...hat.com, riel@...hat.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH mmotm] ksm: stop scan skipping pages
KSM can be slow to identify all mergeable pages. There's an off-by-one
in how ksm_scan_start() proceeds (see how it does a scan_get_next_index
at the head of its loop, but also on leaving its loop), which causes it
to skip over a page occasionally. Fix that.
Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
---
mm/ksm.c | 46 +++++++++++++++++++---------------------------
1 file changed, 19 insertions(+), 27 deletions(-)
--- mmotm/mm/ksm.c 2009-06-08 13:14:36.000000000 +0100
+++ fixed/mm/ksm.c 2009-06-08 13:18:30.000000000 +0100
@@ -1331,30 +1331,26 @@ out:
/* return -EAGAIN - no slots registered, nothing to be done */
static int scan_get_next_index(struct ksm_scan *ksm_scan)
{
- struct ksm_mem_slot *slot;
+ struct list_head *next;
if (list_empty(&slots))
return -EAGAIN;
- slot = ksm_scan->slot_index;
-
/* Are there pages left in this slot to scan? */
- if ((slot->npages - ksm_scan->page_index - 1) > 0) {
- ksm_scan->page_index++;
+ ksm_scan->page_index++;
+ if (ksm_scan->page_index < ksm_scan->slot_index->npages)
return 0;
- }
- list_for_each_entry_from(slot, &slots, link) {
- if (slot == ksm_scan->slot_index)
- continue;
- ksm_scan->page_index = 0;
- ksm_scan->slot_index = slot;
+ ksm_scan->page_index = 0;
+ next = ksm_scan->slot_index->link.next;
+ if (next != &slots) {
+ ksm_scan->slot_index =
+ list_entry(next, struct ksm_mem_slot, link);
return 0;
}
/* look like we finished scanning the whole memory, starting again */
root_unstable_tree = RB_ROOT;
- ksm_scan->page_index = 0;
ksm_scan->slot_index = list_first_entry(&slots,
struct ksm_mem_slot, link);
return 0;
@@ -1366,21 +1362,22 @@ static int scan_get_next_index(struct ks
* pointed to was released so we have to call this function every time after
* taking the slots_lock
*/
-static void scan_update_old_index(struct ksm_scan *ksm_scan)
+static int scan_update_old_index(struct ksm_scan *ksm_scan)
{
struct ksm_mem_slot *slot;
if (list_empty(&slots))
- return;
+ return -EAGAIN;
list_for_each_entry(slot, &slots, link) {
if (ksm_scan->slot_index == slot)
- return;
+ return 0;
}
ksm_scan->slot_index = list_first_entry(&slots,
struct ksm_mem_slot, link);
ksm_scan->page_index = 0;
+ return 0;
}
/**
@@ -1399,20 +1396,14 @@ static int ksm_scan_start(struct ksm_sca
struct ksm_mem_slot *slot;
struct page *page[1];
int val;
- int ret = 0;
+ int ret;
down_read(&slots_lock);
+ ret = scan_update_old_index(ksm_scan);
- scan_update_old_index(ksm_scan);
-
- while (scan_npages > 0) {
- ret = scan_get_next_index(ksm_scan);
- if (ret)
- goto out;
-
- slot = ksm_scan->slot_index;
-
+ while (scan_npages && !ret) {
cond_resched();
+ slot = ksm_scan->slot_index;
/*
* If the page is swapped out or in swap cache, we don't want to
@@ -1433,10 +1424,11 @@ static int ksm_scan_start(struct ksm_sca
} else {
up_read(&slot->mm->mmap_sem);
}
+
+ ret = scan_get_next_index(ksm_scan);
scan_npages--;
}
- scan_get_next_index(ksm_scan);
-out:
+
up_read(&slots_lock);
return ret;
}
--
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