On 11/10/2025 7:16 PM, Dev Jain wrote:

On 10/11/25 5:02 pm, Shivank Garg wrote:

quoted

When MADV_COLLAPSE encounters dirty file-backed pages, it currently
returns -EINVAL, this is misleading as EINVAL suggests invalid arguments,
whereas dirty pages are a transient condition that may resolve on retry.

Introduce SCAN_PAGE_DIRTY and map it to -EAGAIN. For khugepaged, this
is harmless as it will revisit the range after async writeback completes.

Taking a cursory look at enum scan_result, I am sure there are other error
codes as well which redirect to -EINVAL when they actually should to something
else...

quoted

quoted

@@ -1967,7 +1968,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,

                   */
                  xas_unlock_irq(&xas);
                  filemap_flush(mapping);
-                result = SCAN_FAIL;
+                result = SCAN_PAGE_DIRTY;
                  goto xa_unlocked;
              } else if (folio_test_writeback(folio)) {
                  xas_unlock_irq(&xas);

Now that you are at it, it would make sense to redirect this folio_test_writeback()
branch also to -EAGAIN, and call the common error code SCAN_PAGE_UNDER_WRITEBACK.

Good point about the folio_test_writeback() case.
I think we can use a single error code "SCAN_PAGE_NOT_CLEAN" to cover both dirty and writeback states.

Thanks,
Shivank