From: Kiryl Shutsemau <kirill@shutemov.name>
To: "David Hildenbrand (Arm)" <david@kernel.org>
Cc: akpm@linux-foundation.org, usama.anjum@collabora.com,
peterx@redhat.com, liam@infradead.org, ljs@kernel.org,
vbabka@kernel.org, jannh@google.com, pfalcato@suse.de,
rppt@kernel.org, surenb@google.com, mhocko@suse.com,
shuah@kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kselftest@vger.kernel.org, stable@vger.kernel.org,
kernel-team@meta.com
Subject: Re: [PATCH v4] fs/proc/task_mmu: fix PAGEMAP_SCAN written state for PMD holes
Date: Wed, 15 Jul 2026 15:08:15 +0100 [thread overview]
Message-ID: <aleT2uw9glPnKiqv@thinkstation> (raw)
In-Reply-To: <f5700c45-9eab-47e1-946c-47d9a531bfeb@kernel.org>
On Wed, Jul 15, 2026 at 03:47:00PM +0200, David Hildenbrand (Arm) wrote:
> >
> > MADV_DONTNEED has fill-with-zeros semantics: it changes the contents of
> > the range to zeroes (a subsequent read maps the zero page), which write
>
> Only in MAP_PRIVATE | MAP_ANON mappings.
Right, I'll scope the fill-with-zeros wording to MAP_PRIVATE|MAP_ANON.
The fix itself isn't anon-specific -- it covers any non-hugetlb uffd-wp
VMA (anon and shmem); the invariant is just "unpopulated => written",
matching pte_none in pagemap_page_category(). I'll spell that out, along
with the WP_UNPOPULATED marker mechanism (a missing marker == the range
was MADV_DONTNEED'd).
> Do we really want to backport a test case? Usually we split them from the actual
> fix.
Agreed -- v5 will split it.
The rest goes into v5: your shorter comment, reuse of
unpopulated_scan_test()'s sequence, recover instead of ksft_exit on the
mmap failure, and rename to unpopulated_thp_scan_test().
--
Kiryl Shutsemau / Kirill A. Shutemov
prev parent reply other threads:[~2026-07-15 14:08 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-13 9:17 [PATCH v4] fs/proc/task_mmu: fix PAGEMAP_SCAN written state for PMD holes Kiryl Shutsemau
2026-07-15 13:47 ` David Hildenbrand (Arm)
2026-07-15 14:08 ` Kiryl Shutsemau [this message]
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