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Message-ID: <YxkEJhTzglEfo+Tp@monkey>
Date: Wed, 7 Sep 2022 13:50:46 -0700
From: Mike Kravetz <mike.kravetz@...cle.com>
To: Miaohe Lin <linmiaohe@...wei.com>
Cc: Muchun Song <songmuchun@...edance.com>,
David Hildenbrand <david@...hat.com>,
Michal Hocko <mhocko@...e.com>, Peter Xu <peterx@...hat.com>,
Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
"Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
Andrea Arcangeli <aarcange@...hat.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Davidlohr Bueso <dave@...olabs.net>,
Prakash Sangappa <prakash.sangappa@...cle.com>,
James Houghton <jthoughton@...gle.com>,
Mina Almasry <almasrymina@...gle.com>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Ray Fucillo <Ray.Fucillo@...ersystems.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/8] hugetlb: add vma based lock for pmd sharing
On 08/29/22 15:24, Mike Kravetz wrote:
> On 08/27/22 17:30, Miaohe Lin wrote:
> > On 2022/8/25 1:57, Mike Kravetz wrote:
> > > Allocate a rw semaphore and hang off vm_private_data for
> > > synchronization use by vmas that could be involved in pmd sharing. Only
> > > add infrastructure for the new lock here. Actual use will be added in
> > > subsequent patch.
> > >
> > > Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> >
> > <snip>
> >
> > > +static void hugetlb_vma_lock_free(struct vm_area_struct *vma)
> > > +{
> > > + /*
> > > + * Only present in sharable vmas. See comment in
> > > + * __unmap_hugepage_range_final about the neeed to check both
> >
> > s/neeed/need/
> >
> > > + * VM_SHARED and VM_MAYSHARE in free path
> >
> > I think there might be some wrong checks around this patch. As above comment said, we
> > need to check both flags, so we should do something like below instead?
> >
> > if (!(vma->vm_flags & (VM_MAYSHARE | VM_SHARED) == (VM_MAYSHARE | VM_SHARED)))
> >
> > > + */
>
> Thanks. I will update.
>
> > > + if (!vma || !(vma->vm_flags & (VM_MAYSHARE | VM_SHARED)))
> > > + return;
I think you misunderstood the comment which I admit was not very clear. And,
I misunderstood your suggestion. I believe the code is correct as it. Here
is the proposed update comment/code:
/*
* Only present in sharable vmas. See comment in
* __unmap_hugepage_range_final about how VM_SHARED could
* be set without VM_MAYSHARE. As a result, we need to
* check if either is set in the free path.
*/
if (!vma || !(vma->vm_flags & (VM_MAYSHARE | VM_SHARED)))
return;
Hopefully, that makes more sense.
--
Mike Kravetz
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