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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: [RESEND v7 23/29] mm/khugepaged: treat PMD swap entries as mapped THPs Date: Mon, 14 Sep 2026 05:28:13 -0700 Message-ID: <20260914122950.3283997-24-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260914122950.3283997-1-usama.arif@linux.dev> References: <20260914122950.3283997-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1320E2000F X-Stat-Signature: akbh574sm5cg6pktiw4wn86n5314a6jk X-Rspam-User: X-HE-Tag: 1789389123-24174 X-HE-Meta: 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 oq2AoP8W mM90NojqNS5G/PjSL657BGlZCT1i3U6WR8x+YAaZiUEPR/MPxEdz27EJXdT+Oq3CaLvyl4K5dYx8+iQaX9nxeu8XVnvSyL4DKI9xB0WFLCL3z70nAGNeg61QmXxPyI6GGBBtBMFlJlJW4N8Bq8kwFD1mJ6+Je2SO/Ru2YxIcviCLKfPIiglZ8CkGeVUKwxi4ejxrvRIfWeAM1SObf4Oappw/dgE+AiJOTze9Q Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 0d8cd44b14c57..bbbf96c616295 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1052,6 +1052,12 @@ 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