Messages in this thread | | | Subject | Re: [PATCH] mm/page_isolation: don't putback unisolated page | From | David Hildenbrand <> | Date | Mon, 6 Sep 2021 14:11:13 +0200 |
| |
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@huawei.com> >> --- >> 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@redhat.com> >
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?
-- Thanks,
David / dhildenb
| |