On 19.06.23 09:56, David Hildenbrand wrote:
On 19.06.23 05:59, Yosry Ahmed wrote:
On Sun, Jun 18, 2023 at 7:00 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote:
Hi, Yosry,
Yosry Ahmed <yosryahmed@xxxxxxxxxx> writes:
This reverts commit c3096e6782b733158bf34f6bbb4567808d4e0740.
That commit made sure we immediately add the new page to the LRU before
remove_migration_ptes() is called in migrate_move_folio() (used to be
__unmap_and_move() back then), such that the rmap walk will rebuild the
correct mlock_count for the page again. This was needed because the
mlock_count was lost when the page is isolated. This is no longer the
case since mlock_count no longer overlays page->lru.
Revert the commit (the code was foliated afterward the commit, so the
revert is updated as such).
Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---
mm/migrate.c | 24 +++++++++---------------
1 file changed, 9 insertions(+), 15 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 01cac26a3127..68f693731865 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1279,19 +1279,6 @@ static int migrate_folio_move(free_page_t put_new_page, unsigned long private,
if (unlikely(!is_lru))
goto out_unlock_both;
The patch itself looks good to me! Thanks!
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Thanks for taking a look!
And, it seems that we can remove the above 2 lines and "out_unlock_both"
label now. That can make the code simpler a little. Right?
I am not familiar with this code. If we remove the above condition
then pages that have is_lru == 0 (i.e __PageMovable(src) is true) and
page_was_mapped == 1 will call remove_migration_ptes(). This wouldn't
happen without removing the above 2 lines. If this combination is
impossible (is_lru == 0 && page_was_mapped == 1), then yeah we can
remove the above condition.
It looks like __SetPageMovable() is only called by zsmalloc, z3fold,
and balloon_page_insert(). The former 2 will never have those pages
mapped into userspace. I am not familiar with balloon_page_insert(),
but my gut feeling is that those are pages used by the driver and are
also not mapped into userspace.
On XEN, there is xen_alloc_ballooned_pages(), which ends up mapping
balloon-inflated pages into user space (for something like MMIO IIRC).
But the XEN balloon does not use the balloon compaction framework, so
__SetPageMovable() does not apply.
The other balloon_page_insert() users (VMware balloon, CMM,
virtio-balloon) shouldn't be doing something like that.
Ah, and I remember they even can't, because in balloon_page_insert() we
also do a __SetPageOffline(). And such typed pages cannot be mapped into
user space (because the type overlays the mapcount).
--
Cheers,
David / dhildenb
