On Thu 05-12-19 12:21:18, Yang Shi wrote:
Felix Abecassis reports move_pages() would return random status if the
pages are already on the target node by the below test program:
---8<---
int main(void)
{
const long node_id = 1;
const long page_size = sysconf(_SC_PAGESIZE);
const int64_t num_pages = 8;
unsigned long nodemask = 1 << node_id;
long ret = set_mempolicy(MPOL_BIND, &nodemask, sizeof(nodemask));
if (ret < 0)
return (EXIT_FAILURE);
void **pages = malloc(sizeof(void*) * num_pages);
for (int i = 0; i < num_pages; ++i) {
pages[i] = mmap(NULL, page_size, PROT_WRITE | PROT_READ,
MAP_PRIVATE | MAP_POPULATE | MAP_ANONYMOUS,
-1, 0);
if (pages[i] == MAP_FAILED)
return (EXIT_FAILURE);
}
ret = set_mempolicy(MPOL_DEFAULT, NULL, 0);
if (ret < 0)
return (EXIT_FAILURE);
int *nodes = malloc(sizeof(int) * num_pages);
int *status = malloc(sizeof(int) * num_pages);
for (int i = 0; i < num_pages; ++i) {
nodes[i] = node_id;
status[i] = 0xd0; /* simulate garbage values */
}
ret = move_pages(0, num_pages, pages, nodes, status, MPOL_MF_MOVE);
printf("move_pages: %ld\n", ret);
for (int i = 0; i < num_pages; ++i)
printf("status[%d] = %d\n", i, status[i]);
}
---8<---
Then running the program would return nonsense status values:
$ ./move_pages_bug
move_pages: 0
status[0] = 208
status[1] = 208
status[2] = 208
status[3] = 208
status[4] = 208
status[5] = 208
status[6] = 208
status[7] = 208
This is because the status is not set if the page is already on the
target node, but move_pages() should return valid status as long as it
succeeds. The valid status may be errno or node id.
We can't simply initialize status array to zero since the pages may be
not on node 0. Fix it by updating status with node id which the page is
already on. And, it looks we have to update the status inside
add_page_for_migration() since the page struct is not available outside
it.
The code is indeed more complex than I wanted but I couldn't figure an
easier way back then. I wanted to keep store_status at a single place
because the failure handling is quite complex already.
Make add_page_for_migration() return 1 if store_status() is failed in
order to not mix up the status value since -EFAULT is also a valid
status.
Can we simply return 1 when there is something to migrate instead?
Something like
diff --git a/mm/migrate.c b/mm/migrate.c
index 4fe45d1428c8..f3730804b8d4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1516,9 +1516,9 @@ static int do_move_pages_to_node(struct mm_struct *mm,
/*
* Resolves the given address to a struct page, isolates it from the LRU and
* puts it to the given pagelist.
- * Returns -errno if the page cannot be found/isolated or 0 when it has been
- * queued or the page doesn't need to be migrated because it is already on
- * the target node
+ * Returns -errno if the page cannot be found/isolated or 0 when it doesn't have
+ * to be migrate or 1 dwhen it has been queued or the page doesn't need to be
+ * migrated because it is already on the target node
*/
static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
int node, struct list_head *pagelist, bool migrate_all)
@@ -1557,7 +1557,7 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
if (PageHuge(page)) {
if (PageHead(page)) {
isolate_huge_page(page, pagelist);
- err = 0;
+ err = 1;
}
} else {
struct page *head;
@@ -1567,7 +1567,7 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
if (err)
goto out_putpage;
- err = 0;
+ err = 1;
list_add_tail(&head->lru, pagelist);
mod_node_page_state(page_pgdat(head),
NR_ISOLATED_ANON + page_is_file_cache(head),
@@ -1644,8 +1644,14 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
*/
err = add_page_for_migration(mm, addr, current_node,
&pagelist, flags & MPOL_MF_MOVE_ALL);
- if (!err)
+ if (!err) {
+ err = store_status(status, i, current_node, 1);
+ if (err)
+ goto out_flush;
+ continue;
+ } else if (err > 0) {
continue;
+ }
err = store_status(status, i, err, 1);
if (err)
this would still keep store_status ugliness at a single place.
