When MADV_COLLAPSE is called on file-backed mappings (e.g., executable text sections), the pages may still be dirty from recent writes. collapse_file() will trigger async writeback and fail with SCAN_PAGE_DIRTY_OR_WRITEBACK (-EAGAIN).
MADV_COLLAPSE is a synchronous operation where userspace expects immediate results. If the collapse fails due to dirty pages, perform synchronous writeback on the specific range and retry once. This avoids spurious failures for freshly written executables while avoiding unnecessary synchronous I/O for mappings that are already clean. Reported-by: Branden Moore <[email protected]> Closes: https://lore.kernel.org/all/[email protected] Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE") Suggested-by: David Hildenbrand <[email protected]> Tested-by: Lance Yang <[email protected]> Signed-off-by: Shivank Garg <[email protected]> --- mm/khugepaged.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 219dfa2e523c..16582bdcb6ff 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -22,6 +22,7 @@ #include <linux/dax.h> #include <linux/ksm.h> #include <linux/pgalloc.h> +#include <linux/backing-dev.h> #include <asm/tlb.h> #include "internal.h" @@ -2788,7 +2789,9 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { int result = SCAN_FAIL; + bool triggered_wb = false; +retry: if (!mmap_locked) { cond_resched(); mmap_read_lock(mm); @@ -2809,8 +2812,20 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, mmap_read_unlock(mm); mmap_locked = false; + *lock_dropped = true; result = hpage_collapse_scan_file(mm, addr, file, pgoff, cc); + + if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb && + mapping_can_writeback(file->f_mapping)) { + loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; + loff_t lend = lstart + HPAGE_PMD_SIZE - 1; + + filemap_write_and_wait_range(file->f_mapping, lstart, lend); + triggered_wb = true; + fput(file); + goto retry; + } fput(file); } else { result = hpage_collapse_scan_pmd(mm, vma, addr, -- 2.43.0
