Re: [PATCH v2 1/4] mm/filemap: Add folio_lock_timeout()

Matthew Wilcox
2023-04-27T02:16:49Z

On Wed, Apr 26, 2023 at 02:39:56PM -0700, Doug Anderson wrote:
> Sure, I'm happy to do it like you say. Do you have any suggestions for
> the similar lock_buffer() case, or are you OK w/ the timeout there?

I'd do that similarly, ie:

+++ b/mm/migrate.c
@@ -691,38 +691,30 @@ EXPORT_SYMBOL(migrate_folio);
static bool buffer_migrate_lock_buffers(struct buffer_head *head,
enum migrate_mode mode)
{
- struct buffer_head *bh = head;
+ struct buffer_head *failed_bh, *bh = head;

- /* Simple case, sync compaction */
- if (mode != MIGRATE_ASYNC) {
- do {
- lock_buffer(bh);
- bh = bh->b_this_page;
-
- } while (bh != head);
-
- return true;
- }
-
- /* async case, we cannot block on lock_buffer so use trylock_buffer */
do {
if (!trylock_buffer(bh)) {
- /*
- * We failed to lock the buffer and cannot stall in
- * async migration. Release the taken locks
- */
- struct buffer_head *failed_bh = bh;
- bh = head;
- while (bh != failed_bh) {
- unlock_buffer(bh);
- bh = bh->b_this_page;
- }
- return false;
+ if (mode == MIGRATE_ASYNC)
+ goto unlock;
+ if (mode == MIGRATE_SYNC_LIGHT && !buffer_uptodate(bh))
+ goto unlock;
+ lock_buffer(bh);
}

bh = bh->b_this_page;
} while (bh != head);
return true;
+
+unlock:
+ /* Failed to lock the buffer and cannot stall */
+ failed_bh = bh;
+ bh = head;
+ while (bh != failed_bh) {
+ unlock_buffer(bh);
+ bh = bh->b_this_page;
+ }
+ return false;
}

static int __buffer_migrate_folio(struct address_space *mapping,