@@ -2374,6 +2374,7 @@ static int madvise_collapse_errno(enum scan_result r)
/* Resource temporary unavailable - trying again might succeed */
case SCAN_PAGE_LOCK:
case SCAN_PAGE_LRU:
+ case SCAN_DEL_PAGE_LRU:
return -EAGAIN;
/*
* Other: Trying again likely not to succeed / error intrinsic to
@@ -2456,6 +2457,7 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
case SCAN_PAGE_LOCK:
case SCAN_PAGE_COMPOUND:
case SCAN_PAGE_LRU:
+ case SCAN_DEL_PAGE_LRU:
last_fail = result;
break;
default:
MADV_COLLAPSE is a best-effort request that attempts to set an actionable errno value if the request cannot be fulfilled at the time. EAGAIN should be used to communicate that a resource was temporarily unavailable, but that the user may try again immediately. SCAN_DEL_PAGE_LRU is an internal result code used when a page cannot be isolated from it's LRU list. Since this, like SCAN_PAGE_LRU, is likely a transitory state, make MADV_COLLAPSE return EAGAIN so that users know they may reattempt the operation. Another important scenario to consider is race with khugepaged. khugepaged might isolate a page while MADV_COLLAPSE is interested in it. Even though racing with khugepaged might mean that the memory has already been collapsed, signalling an errno that is non-intrinsic to that memory or arguments provided to madvise(2) lets the user know that future attempts might (and in this case likely would) succeed, and avoids false-negative assumptions by the user. Fixes: 7d8faaf15545 ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse") Signed-off-by: Zach O'Keefe <zokeefe@google.com> --- mm/khugepaged.c | 2 ++ 1 file changed, 2 insertions(+)