On 20/11/25 12:20 pm, Shivank Garg wrote:
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 <[email protected]>
---
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
SCAN_PAGE_NOT_CLEAN is confusing - NOT_CLEAN literally means dirty, so why not
SCAN_PAGE_DIRTY?
Or SCAN_PAGE_DIRTY_OR_UNDER_WRITEBACK? Since folio_test_writeback() is true as
a result of
the folio being dirty, maybe just SCAN_PAGE_DIRTY can do.
Reviewed-by: Dev Jain <[email protected]>
