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Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com, Usama Arif Subject: [PATCH v9 23/32] mm/madvise: skip PMD swap entries for MADV_COLD and MADV_PAGEOUT Date: Thu, 5 Nov 2026 10:39:07 -0800 Message-ID: <20261105183940.2236717-24-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261105183940.2236717-1-usama.arif@linux.dev> References: <20261105183940.2236717-1-usama.arif@linux.dev> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit A swapped-out THP has no resident folio to deactivate or reclaim, which is also the conclusion the PTE path reaches when it walks the swap entries and skips every one. madvise_cold_or_pageout_pte_range() gets there the long way round: pmd_trans_huge() is false for a PMD swap entry, so it falls out of the huge branch and tries to map a PTE table that a non-present PMD does not have. The entry can also appear after that first, lockless test, so re-check under the PMD lock; otherwise a PMD that turned into a swap entry while pmd_trans_huge_lock() was being taken trips the VM_WARN_ON_ONCE() that expects a migration or device-private entry. Signed-off-by: Usama Arif --- mm/madvise.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/mm/madvise.c b/mm/madvise.c index 156290227c236..576707e303cf2 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -384,6 +384,15 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, !can_do_file_pageout(vma); #ifdef CONFIG_TRANSPARENT_HUGEPAGE + /* + * Swapped-out THPs have no resident folio to deactivate or reclaim. + * Avoid descending into or splitting a PMD swap entry. + */ + if (pmd_is_swap_entry(*pmd)) { + walk->action = ACTION_CONTINUE; + return 0; + } + if (pmd_trans_huge(*pmd)) { pmd_t orig_pmd; unsigned long next = pmd_addr_end(addr, end); @@ -394,6 +403,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, return 0; orig_pmd = *pmd; + if (pmd_is_swap_entry(orig_pmd)) + goto huge_unlock; + if (unlikely(!pmd_present(orig_pmd))) { VM_WARN_ON_ONCE(!pmd_is_migration_entry(orig_pmd) && !pmd_is_device_private_entry(orig_pmd)); -- 2.53.0-Meta