MADV_COLLAPSE on file-backed mappings fails with -EINVAL when TEXT pages are dirty. This may affect real scenarios: package/container updates, executing binaries immediately after writing them, etc.
The issue is that collapse_file() triggers async writeback and returns SCAN_FAIL (maps to -EINVAL), expecting khugepaged to revisit later. But MADV_COLLAPSE is synchronous and userspace expects immediate success or a clear retry signal. Reproduction: - Copy 2MB-aligned executable to freshly mounted XFS/ext4 - Call MADV_COLLAPSE on .text section - First call fails with -EINVAL (text pages dirty from copy) - Second call succeeds (async writeback completed) Issue Report: https://lore.kernel.org/all/[email protected] v2: - Move writeback to madvise_collapse() (better abstraction, proper mmap_lock handling and does VMA revalidation after I/O) (Lorenzo) - Rename to SCAN_PAGE_DIRTY to SCAN_PAGE_NOT_CLEAN and extend its use for all dirty/writeback folio cases that previously returned incorrect results (Dev) v1: https://lore.kernel.org/all/[email protected] Shivank Garg (2): mm/khugepaged: do synchronous writeback for MADV_COLLAPSE mm/khugepaged: map dirty/writeback pages failures to EAGAIN include/trace/events/huge_memory.h | 3 ++- mm/khugepaged.c | 34 +++++++++++++++++++++++++++--- 2 files changed, 33 insertions(+), 4 deletions(-) base-commit: 4a3f8fc3adb7046e44bd1feb2f5c5fe95296894f -- 2.43.0
