From: Kiryl Shutsemau <kas@kernel.org>
To: Konstantin Khorenko <khorenko@virtuozzo.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"David Hildenbrand (Arm)" <david@kernel.org>,
"Zi Yan" <ziy@nvidia.com>,
"Baolin Wang" <baolin.wang@linux.alibaba.com>,
"Liam R. Howlett" <liam@infradead.org>,
"Nico Pache" <nico.pache@linux.dev>,
"Ryan Roberts" <ryan.roberts@arm.com>,
"Dev Jain" <dev.jain@arm.com>, "Barry Song" <baohua@kernel.org>,
"Lance Yang" <lance.yang@linux.dev>,
"Usama Arif" <usama.arif@linux.dev>,
"Peter Xu" <peterx@redhat.com>,
"Alex Williamson" <alex@shazbot.org>,
kvm@vger.kernel.org,
"Loïc Molinari" <loic.molinari@collabora.com>,
"Lorenzo Stoakes" <ljs@kernel.org>,
"Shuah Khan" <shuah@kernel.org>,
linux-kselftest@vger.kernel.org, dri-devel@lists.freedesktop.org,
"Madhavan Srinivasan" <maddy@linux.ibm.com>,
"Ritesh Harjani (IBM)" <ritesh.list@gmail.com>,
linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, "Jason Gunthorpe" <jgg@ziepe.ca>
Subject: Re: [PATCH v4 4/4] selftests/mm: test fork of PMD-mapped shmem THPs
Date: Tue, 27 Oct 2026 14:51:43 +0000 [thread overview]
Message-ID: <auC4eUEN52PJF1bM@thinkstation> (raw)
In-Reply-To: <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-4-66f00b7a564c@virtuozzo.com>
On Wed, Oct 21, 2026 at 10:36:03PM +0200, Konstantin Khorenko wrote:
> + /* The child's exit took the parent's share off the counter. */
> + if (*after < own || *before - *after >= own)
> + return FAIL_COUNTER;
> + if (*after != *before)
> + return CHANGED;
> + if (mem[pmdsize] != (shared ? 'c' : 2) || !data_ok(mem, size, pmdsize) ||
> + !check_huge_shmem(mem, size - pmdsize, NR_PMDS - 1, pmdsize))
> + return FAIL_PARENT;
ShmemPmdMapped is system-wide. A drop of 'own' or more from another
process between the two reads fails the test instead of being retried
as CHANGED.
The parent's THPs can also lose their PMDs during the test: reclaim can
swap one out, and NUMA balancing can migrate one, which leaves the
counter low while the migration entry is in place. That gives
FAIL_COUNTER, or FAIL_PARENT from the exact count in check_huge_shmem().
--
Kiryl Shutsemau / Kirill A. Shutemov
prev parent reply other threads:[~2026-10-27 14:51 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 20:35 [PATCH v4 0/4] mm/huge_memory: copy PMDs at fork like the PTE path does Konstantin Khorenko
2026-10-21 20:36 ` [PATCH v4 1/4] mm/rmap: duplicate a PMD mapping as one in folio_dup_file_rmap_pmd() Konstantin Khorenko
2026-10-21 20:43 ` Zi Yan
2026-10-22 10:34 ` Konstantin Khorenko
2026-10-22 8:07 ` Lorenzo Stoakes (ARM)
2026-10-22 10:44 ` Konstantin Khorenko
2026-10-22 12:11 ` Lorenzo Stoakes (ARM)
2026-10-22 14:16 ` Konstantin Khorenko
2026-10-27 14:06 ` David Hildenbrand (Arm)
2026-10-27 13:53 ` Kiryl Shutsemau
2026-10-27 14:06 ` David Hildenbrand (Arm)
2026-10-21 20:36 ` [PATCH v4 2/4] mm/huge_memory: copy file THPs at fork like copy_present_ptes() does Konstantin Khorenko
2026-10-27 14:08 ` Kiryl Shutsemau
2026-10-27 14:39 ` David Hildenbrand (Arm)
2026-10-21 20:36 ` [PATCH v4 3/4] mm/huge_memory: read a special PMD under the lock in copy_huge_pmd() Konstantin Khorenko
2026-10-27 14:24 ` Kiryl Shutsemau
2026-10-27 14:42 ` David Hildenbrand (Arm)
2026-10-21 20:36 ` [PATCH v4 4/4] selftests/mm: test fork of PMD-mapped shmem THPs Konstantin Khorenko
2026-10-27 14:51 ` Kiryl Shutsemau [this message]
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