[PATCH V2 2/2] mm/khugepaged: map dirty/writeback pages failures to EAGAIN
From: Shivank Garg <hidden>
Date: 2025-11-20 06:55:24
Also in:
linux-mm, lkml
Subsystem:
memory management, memory management - thp (transparent huge page), the rest, tracing · Maintainers:
Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
When collapse_file encounters dirty or writeback pages in file-backed mappings, it currently SCAN_FAIL which maps to -EINVAL. This is misleading as EINVAL suggests invalid arguments, whereas dirty/writeback pages represent transient conditions that may resolve on retry. Introduce SCAN_PAGE_NOT_CLEAN to cover both dirty and writeback states, mapping it to -EAGAIN. For MADV_COLLAPSE, this provides userspace with a clear signal that retry may succeed after writeback completes, making -EAGAIN semantically correct. For khugepaged, this is harmless as it will naturally revisit the range during periodic scans after async writeback completes. Signed-off-by: Shivank Garg <redacted> --- include/trace/events/huge_memory.h | 3 ++- mm/khugepaged.c | 8 +++++--- 2 files changed, 7 insertions(+), 4 deletions(-)
diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 4cde53b45a85..1caf24b951e1 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h@@ -37,7 +37,8 @@ EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ EM( SCAN_STORE_FAILED, "store_failed") \ EM( SCAN_COPY_MC, "copy_poisoned_page") \ - EMe(SCAN_PAGE_FILLED, "page_filled") + EM( SCAN_PAGE_FILLED, "page_filled") \ + EMe(SCAN_PAGE_NOT_CLEAN, "page_not_clean") #undef EM #undef EMe
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 066a332c76ad..282b413d17e8 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c@@ -59,6 +59,7 @@ enum scan_result { SCAN_STORE_FAILED, SCAN_COPY_MC, SCAN_PAGE_FILLED, + SCAN_PAGE_NOT_CLEAN, }; #define CREATE_TRACE_POINTS
@@ -1968,11 +1969,11 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, */ xas_unlock_irq(&xas); filemap_flush(mapping); - result = SCAN_FAIL; + result = SCAN_PAGE_NOT_CLEAN; goto xa_unlocked; } else if (folio_test_writeback(folio)) { xas_unlock_irq(&xas); - result = SCAN_FAIL; + result = SCAN_PAGE_NOT_CLEAN; goto xa_unlocked; } else if (folio_trylock(folio)) { folio_get(folio);
@@ -2019,7 +2020,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, * folio is dirty because it hasn't been flushed * since first write. */ - result = SCAN_FAIL; + result = SCAN_PAGE_NOT_CLEAN; goto out_unlock; }
@@ -2748,6 +2749,7 @@ static int madvise_collapse_errno(enum scan_result r) case SCAN_PAGE_LRU: case SCAN_DEL_PAGE_LRU: case SCAN_PAGE_FILLED: + case SCAN_PAGE_NOT_CLEAN: return -EAGAIN; /* * Other: Trying again likely not to succeed / error intrinsic to
--
2.43.0