Khugepaged will scan/free HPAGE_PMD_NR normal pages and replace with a
hugepage which is allocated from the node of the first scanned normal page, but
this policy is too rough and may end with unexpected result to upper users.
The problem is the original page-balancing among all nodes will be broken
after hugepaged started.
Thinking about the case if the first scanned normal page is allocated from
node A, most of other scanned normal pages are allocated from node B or C..
But hugepaged will always allocate hugepage from node A which will cause extra
memory pressure on node A which is not the situation before khugepaged started.
This patch try to fix this problem by making khugepaged allocate hugepage from
the node which have max record of scaned normal pages hit, so that the effect
to original page-balancing can be minimized.
The other problem is if normal scanned pages are equally allocated from Node A,B
and C, after khugepaged started Node A will still suffer extra memory pressure.
Andrew Davidoff reported a related issue several days ago.
He wanted his application interleaving among all nodes and
"numactl --interleave=all ./test" was used to run the testcase, but the result
wasn't not as expected.
cat /proc/2814/numa_maps:
7f50bd440000 interleave:0-3 anon=51403 dirty=51403 N0=435 N1=435 N2=435
N3=50098
The end result showed that most pages are from Node3 instead of interleave
among node0-3 which was unreasonable.
This patch also fix this issue by allocating hugepage round robin from all
nodes have the same record, after this patch the result was as expected:
7f78399c0000 interleave:0-3 anon=51403 dirty=51403 N0=12723 N1=12723 N2=13235
N3=12722
The simple testcase is like this:
int main() {
char *p;
int i;
int j;
for (i=0; i < 200; i++) {
p = (char *)malloc(1048576);
printf("malloc done\n");
if (p == 0) {
printf("Out of memory\n");
return 1;
}
for (j=0; j < 1048576; j++) {
p[j] = 'A';
}
printf("touched memory\n");
sleep(1);
}
printf("enter sleep\n");
while(1) {
sleep(100);
}
}
Reported-by: Andrew Davidoff <davidoff@xxxxxxxxx>
Tested-by: Andrew Davidoff <davidoff@xxxxxxxxx>
Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
---
mm/huge_memory.c | 52 +++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 43 insertions(+), 9 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7448cf9..0d0f40b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2144,7 +2144,33 @@ static void khugepaged_alloc_sleep(void)
msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
}
+static int khugepaged_node_load[MAX_NUMNODES];
#ifdef CONFIG_NUMA
+static int last_khugepaged_target_node = NUMA_NO_NODE;
+static int khugepaged_find_target_node(void)
+{
+ int nid, target_node = 0, max_value = 0;
+
+ /* find first node with max normal pages hit */
+ for (nid = 0; nid < MAX_NUMNODES; nid++)
+ if (khugepaged_node_load[nid] > max_value) {
+ max_value = khugepaged_node_load[nid];
+ target_node = nid;
+ }
+
+ /* do some balance if several nodes have the same hit record */
+ if (target_node <= last_khugepaged_target_node)
+ for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
+ nid++)
+ if (max_value == khugepaged_node_load[nid]) {
+ target_node = nid;
+ break;
+ }
+
+ last_khugepaged_target_node = target_node;
+ return target_node;
+}
+
static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
{
if (IS_ERR(*hpage)) {
@@ -2178,9 +2204,8 @@ static struct page
* mmap_sem in read mode is good idea also to allow greater
* scalability.
*/
- *hpage = alloc_hugepage_vma(khugepaged_defrag(), vma, address,
- node, __GFP_OTHER_NODE);
-
+ *hpage = alloc_pages_exact_node(node, alloc_hugepage_gfpmask(
+ khugepaged_defrag(), __GFP_OTHER_NODE), HPAGE_PMD_ORDER);
/*
* After allocating the hugepage, release the mmap_sem read lock in
* preparation for taking it in write mode.
@@ -2196,6 +2221,11 @@ static struct page
return *hpage;
}
#else
+static int khugepaged_find_target_node(void)
+{
+ return 0;
+}
+
static inline struct page *alloc_hugepage(int defrag)
{
return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
@@ -2405,6 +2435,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
if (pmd_trans_huge(*pmd))
goto out;
+ memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, _address += PAGE_SIZE) {
@@ -2421,12 +2452,13 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
if (unlikely(!page))
goto out_unmap;
/*
- * Chose the node of the first page. This could
- * be more sophisticated and look at more pages,
- * but isn't for now.
+ * Record which node the original page is from and save this
+ * information to khugepaged_node_load[].
+ * Khupaged will allocate hugepage from the node has the max
+ * hit record.
*/
- if (node == NUMA_NO_NODE)
- node = page_to_nid(page);
+ node = page_to_nid(page);
+ khugepaged_node_load[node]++;
VM_BUG_ON(PageCompound(page));
if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
goto out_unmap;
@@ -2441,9 +2473,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
ret = 1;
out_unmap:
pte_unmap_unlock(pte, ptl);
- if (ret)
+ if (ret) {
+ node = khugepaged_find_target_node();
/* collapse_huge_page will return with the mmap_sem released */
collapse_huge_page(mm, address, hpage, vma, node);
+ }
out:
return ret;
}
--
1.7.10.4
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