Messages in this thread | | | Subject | Re: [PATCH] mm/page_isolation: don't putback unisolated page | From | David Hildenbrand <> | Date | Tue, 7 Sep 2021 11:52:51 +0200 |
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On 07.09.21 03:46, Miaohe Lin wrote: > On 2021/9/6 20:49, David Hildenbrand wrote: >> 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@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? >>> >>> 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); > > Should this be VM_BUG_ON(!isolated_page) ? >
Ehm, yes :)
-- Thanks,
David / dhildenb
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