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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 26/32] mm/khugepaged: treat PMD swap entries as mapped THPs Date: Thu, 5 Nov 2026 10:39:10 -0800 Message-ID: <20261105183940.2236717-27-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-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 8C12D140008 X-Stat-Signature: rrbs6eke7h8dnwihsdzidqrw914bbx4k X-Rspam-User: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793904130-568433 X-HE-Meta: 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 rwBT6ktC BQkcaCvkI4D/dTUQ2PkYvHNorW5sWenlxtQuMW8a2SpmB8xWSuWV7IXZBKZi+Ou8EthlykpxBsQw/zDUONW8oe2zjOHV/U62jQE0s9vTnFKy1J0RJXB9VShu1SwagIzOqMALmjEhqUzgFS0qOgo76N7+Qm7gm3E6y3YBr/xKxzWqW/1CBeSKTMqjcZ8xrMD0OKxjgI4U1MazZDJDELadCc7JxWI6gHc1JSfeBPIfTNNysdxI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 check_pmd_state() would report a PMD swap entry as SCAN_NO_PTE_TABLE - it is not present and, on x86, is also pmd_bad(). The range is already a THP; it just happens to be on disk. Return SCAN_PMD_MAPPED next to the existing migration-entry case and before the pmd_present() and pmd_bad() tests. This does change MADV_COLLAPSE. Today a swapped-out THP is HPAGE_PMD_NR PTE swap entries and MADV_COLLAPSE, which ignores khugepaged_max_ptes_swap, swaps them all in. With a PMD swap entry it reports SCAN_PMD_MAPPED, which madvise_collapse() counts as success, so the call returns 0 without making the range resident. It still faults back in as a whole THP on first touch; only the point at which the I/O happens moves. Signed-off-by: Usama Arif --- mm/khugepaged.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index da91762f6358f..b900037bb43c4 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1065,6 +1065,12 @@ static inline enum scan_result check_pmd_state(pmd_t *pmd) */ if (pmd_is_migration_entry(pmde)) return SCAN_PMD_MAPPED; + /* + * A PMD-mapped THP that has been swapped out is still a THP from + * khugepaged's perspective; treat it like a present huge PMD. + */ + if (pmd_is_swap_entry(pmde)) + return SCAN_PMD_MAPPED; if (!pmd_present(pmde)) return SCAN_NO_PTE_TABLE; if (pmd_trans_huge(pmde)) -- 2.53.0-Meta