On 06.09.21 14:45, Miaohe Lin wrote:
On 2021/9/6 20:11, David Hildenbrand wrote:
On 06.09.21 14:02, David Hildenbrand wrote:
On 04.09.21 11:18, Miaohe Lin wrote:
If __isolate_free_page() failed, due to zone watermark check, the page is
still on the free list. But this page will be put back to free list again
via __putback_isolated_page() now. This may trigger page->flags checks in
__free_one_page() if PageReported is set. Or we will corrupt the free list
because list_add() will be called for pages already on another list.
Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
mm/page_isolation.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 9bb562d5d194..7d70d772525c 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -93,10 +93,8 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
buddy_pfn = __find_buddy_pfn(pfn, order);
buddy = page + (buddy_pfn - pfn);
- if (!is_migrate_isolate_page(buddy)) {
- __isolate_free_page(page, order);
- isolated_page = true;
- }
+ if (!is_migrate_isolate_page(buddy))
+ isolated_page = !!__isolate_free_page(page, order);
}
}
Thanks!
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
To make the confusion perfect (sorry) :D I tripple-checked:
In unset_migratetype_isolate() we check that is_migrate_isolate_page(page) holds, otherwise we return.
We call __isolate_free_page() only for such pages.
__isolate_free_page() won't perform watermark checks on is_migrate_isolate().
Consequently, __isolate_free_page() should never fail when called from unset_migratetype_isolate()
If that's correct then we could instead maybe add a VM_BUG_ON() and a comment why this can't fail.
Makes sense or am I missing something?
I think you're right. __isolate_free_page() should never fail when called from unset_migratetype_isolate()
as explained by you. But it might be too fragile to reply on the failure conditions of __isolate_free_page().
If that changes, VM_BUG_ON() here might trigger unexpectedly. Or am I just over-worried as failure conditions
of __isolate_free_page() can hardly change?
Maybe
isolated_page = !!__isolate_free_page(page, order);
/*
* Isolating a free page in an isolated pageblock is expected to always
* work as watermarks don't apply here.
*/
VM_BUG_ON(isolated_page);
VM_BUG_ON() allows us to detect any issues when testing. Combined with
the comment it tells everybody messing with __isolate_free_page() what
we expect in this function.
In production system, we would handle it gracefully.
--
Thanks,
David / dhildenb
