On 2018/12/13 下午10:23, Richard Weinberger wrote:
Hello zhangjun,
thanks a lot for bringing this up!
Am Mittwoch, 12. Dezember 2018, 15:13:57 CET schrieb zhangjun:
Because the PagePrivate() in UBIFS is different meanings,
alloc_cma() will fail when one dirty page cache located in
the type of MIGRATE_CMA
If not adjust the 'extra_count' for dirty page,
ubifs_migrate_page() -> migrate_page_move_mapping() will
always return -EAGAIN for:
expected_count += page_has_private(page)
This causes the migration to fail until the page cache is cleaned
In general, PagePrivate() indicates that buff_head is already bound
to this page, and at the same time page_count() will also increase.
But UBIFS set private flag when the cache is dirty, and page_count()
not increase.
Therefore, the expected_count of UBIFS is different from the general
case.
As you noted, UBIFS uses PG_private a little different.
It uses it as marker and when set, the page counter is not incremented,
since no private data is attached.
The migration code assumes that PG_private indicates a counter of +1.
So, we have to pass a extra count of -1 to migrate_page_move_mapping() if
the flag is set.
Just like F2FS does. Not really nice but hey...
Signed-off-by: zhangjun <openzhangj@xxxxxxxxx>
Fixes: 4ac1c17b2044 ("UBIFS: Implement ->migratepage()")
---
fs/ubifs/file.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 1b78f2e..2136a5c 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -1480,8 +1480,15 @@ static int ubifs_migrate_page(struct address_space *mapping,
struct page *newpage, struct page *page, enum migrate_mode mode)
{
int rc;
+ int extra_count;
- rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
+ /*
+ * UBIFS is using PagePrivate() which can have different meanings across
+ * filesystems. So here adjusting the 'extra_count' make it work.
+ */
Please rewrite that comment.
/*
* UBIFS uses PG_private as marker and does not raise the page counter.
* migrate_page_move_mapping() expects a incremented counter if PG_private
* is set. Therefore pass -1 as extra_count for this case.
*/
+ extra_count = 0 - page_has_private(page);
if (page_has_private(page))
extra_count = -1;
That way this corner is much more obvious.
Thanks,
//richard
Hello Richard.
Thank you very much for your help.
1. Can i use your description for comment? like this:
/*
* UBIFS uses PG_private a little different.
* It uses it as marker and when set, the page counter is not incremented,
* since no private data is attached.
* The migration code assumes that PG_private indicates a counter of +1.
* So, we have to pass a extra count of -1 to migrate_page_move_mapping() if
* the flag is set.
*/
2. It's more obvious, but the branch may break the cpu pipeline?
