Messages in this thread | | | From | Shakeel Butt <> | Date | Wed, 7 Jul 2021 13:53:26 -0700 | Subject | Re: [PATCH 2/4] mm/rmap: fix old bug: munlocking THP missed other mlocks |
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On Wed, Jul 7, 2021 at 1:08 PM Hugh Dickins <hughd@google.com> wrote: > > The kernel recovers in due course from missing Mlocked pages: but there > was no point in calling page_mlock() (formerly known as try_to_munlock()) > on a THP, because nothing got done even when it was found to be mapped in > another VM_LOCKED vma. > > It's true that we need to be careful: Mlocked accounting of pte-mapped > THPs is too difficult (so consistently avoided); but Mlocked accounting > of only-pmd-mapped THPs is supposed to work, even when multiple mappings > are mlocked and munlocked or munmapped. Refine the tests. > > There is already a VM_BUG_ON_PAGE(PageDoubleMap) in page_mlock(), so > page_mlock_one() does not even have to worry about that complication. > > (I said the kernel recovers: but would page reclaim be likely to split > THP before rediscovering that it's VM_LOCKED? I've not followed that up.)
I think, yes, page reclaim will split the THP prematurely in this case.
> > Fixes: 9a73f61bdb8a ("thp, mlock: do not mlock PTE-mapped file huge pages") > Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
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