On Wed, Oct 14, 2026 at 01:57:56PM -0400, Gregory Price (Meta) wrote: > A caller that neither owns nor may write a file may page out the COW pages > of a private mapping of it, but not its file pages. When the advised range > only partly covers a large file folio, the folio must be filtered out > before it is split or reclaimed, on separate paths for PMD- and PTE-mapped > folios. > > Check that partial MADV_PAGEOUT by such a caller leaves every page of a > PMD-sized shmem folio resident, both when a PMD maps it and when a mapping > of half of it maps it with PTEs. > ... snip ... > + ASSERT_EQ(madvise(mapping, pmd_size / 2, MADV_PAGEOUT), 0); > + for (offset = 0; offset < pmd_size; offset += page_size) > + ASSERT_TRUE(page_is_present(self->pagemap_fd, > + mapping + offset)); > + assert_filled(_metadata, mapping, pmd_size);
Sashiko reported: The commit message states that the folio must be filtered out before it is split or reclaimed. Since page_is_present() only confirms the pages were not reclaimed, should this test also verify that the underlying folio was not split by the partial-range madvise? I'm fairly sure this is a false-positive. Splitting a file folio unmaps it entirely, so the page_is_present assert would fail. ~Gregory
