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Subject: Re: [PATCH v2] hugetlb: don't delete vma_lock in hugetlb
 MADV_DONTNEED processing
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <Y13CO8iIGfDnV24u@monkey>
Date:   Sat, 29 Oct 2022 17:54:44 -0700
Cc:     Peter Xu <peterx@redhat.com>, Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        David Hildenbrand <david@redhat.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Rik van Riel <riel@surriel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Wei Chen <harperchen1110@gmail.com>, stable@vger.kernel.org
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Message-Id: <7048D2B5-5FA5-4F72-8FDC-A02411CFD71D@gmail.com>
References: <20221023025047.470646-1-mike.kravetz@oracle.com>
 <Y1mpwKpwsiN6u6r7@x1n> <Y1nImUVseAOpXwPv@monkey> <Y1nbErXmHkyrzt8F@x1n>
 <Y1vz7VvQ5zg5KTxk@monkey> <Y1v/x5RRpRjU4b/W@x1n> <Y1xGzR/nHQTJxTCj@monkey>
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To:     Mike Kravetz <mike.kravetz@oracle.com>
Precedence: bulk

On Oct 29, 2022, at 5:15 PM, Mike Kravetz <mike.kravetz@oracle.com> =
wrote:

> zap_page_range is a bit confusing.  It appears that the passed range =
can
> span multiple vmas.  Otherwise, there would be no do while loop.  Yet, =
there
> is only one mmu_notifier_range_init call specifying the passed vma.
>=20
> It appears all callers pass a range entirely within a single vma.
>=20
> The modifications above would work for a range within a single vma.  =
However,
> things would be more complicated if the range can indeed span multiple =
vmas.
> For multiple vmas, we would need to check the first and last vmas for
> pmd sharing.
>=20
> Anyone know more about this seeming confusing behavior?  Perhaps, =
range
> spanning multiple vmas was left over earlier code?

I don=E2=80=99t have personal knowledge, but I noticed that it does not =
make much
sense, at least for MADV_DONTNEED. I tried to batch the TLB flushes =
across
VMAs for madvise=E2=80=99s. [1]

Need to get to it sometime.

[1] =
https://lore.kernel.org/lkml/20210926161259.238054-7-namit@vmware.com/