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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 25/32] mm/mincore: report PMD swap-cache residency Date: Thu, 5 Nov 2026 10:39:09 -0800 Message-ID: <20261105183940.2236717-26-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 mincore_pte_range() reports every page under a huge PMD as resident. That is wrong for a swapped-out one: mincore() would tell userspace that memory it will have to fault in is already in core. A PMD swap entry is only a compact encoding for HPAGE_PMD_NR slots, so answer from the swap cache instead. One PMD-sized folio covering the range makes every page resident exactly when that folio is uptodate; an empty cache makes none of them; and if the folio was split while the entry stayed in place, fall back to looking up each covered slot as mincore_swap() does for a PTE swap entry. Signed-off-by: Usama Arif --- mm/mincore.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 46 insertions(+), 1 deletion(-) diff --git a/mm/mincore.c b/mm/mincore.c index 0fe50f8a7e629..bc144118e039e 100644 --- a/mm/mincore.c +++ b/mm/mincore.c @@ -85,6 +85,48 @@ static unsigned char mincore_swap(swp_entry_t entry, bool shmem) return present; } +#ifdef CONFIG_THP_SWAP +static void mincore_pmd_swap(swp_entry_t entry, unsigned long addr, + unsigned long end, unsigned char *vec) +{ + unsigned long haddr = addr & HPAGE_PMD_MASK; + unsigned long start = (addr - haddr) >> PAGE_SHIFT; + unsigned long nr = (end - addr) >> PAGE_SHIFT; + struct folio *folio; + enum swap_pmd_cache state; + int i; + + state = swap_pmd_cache_lookup(entry, &folio); + if (state == SWAP_PMD_CACHE_HUGE) { + memset(vec, folio_test_uptodate(folio), nr); + folio_put(folio); + return; + } + + if (state == SWAP_PMD_CACHE_EMPTY) { + memset(vec, 0, nr); + return; + } + + /* + * The PMD swap entry is only a compact encoding for consecutive swap + * slots. If the PMD-sized swapcache folio was split, report residency + * from the individual slots covered by this mincore() range. + */ + for (i = 0; i < nr; i++) + vec[i] = mincore_swap(swp_entry(swp_type(entry), + swp_offset(entry) + start + i), + false); +} +#else /* !CONFIG_THP_SWAP */ +static void mincore_pmd_swap(swp_entry_t entry, unsigned long addr, + unsigned long end, unsigned char *vec) +{ + /* Nothing produces PMD swap entries without CONFIG_THP_SWAP. */ + memset(vec, 0, (end - addr) >> PAGE_SHIFT); +} +#endif /* CONFIG_THP_SWAP */ + /* * Later we can get more picky about what "in core" means precisely. * For now, simply check to see if the page is in the page cache, @@ -171,7 +213,10 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, ptl = pmd_trans_huge_lock(pmd, vma); if (ptl) { - memset(vec, 1, nr); + if (pmd_is_swap_entry(*pmd)) + mincore_pmd_swap(softleaf_from_pmd(*pmd), addr, end, vec); + else + memset(vec, 1, nr); spin_unlock(ptl); goto out; } -- 2.53.0-Meta