Re: [PATCH v3] mm: page_alloc: make defrag_mode retries follow the promoted order

[Andrew Morton]

On Fri,  9 Oct 2026 13:55:02 +0100 "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx> wrote:

> Since commit 7e8756d7ad22 ("mm: page_alloc: fix non-movable reclaim
> storm in defrag_mode"), direct reclaim and compaction for non-movable
> requests under defrag_mode run at pageblock_order, to produce the whole
> blocks that ALLOC_NOFRAGMENT needs. The retry decisions that follow
> still use the request order. An order-0 request can therefore retry
> indefinitely without ever reaching the ALLOC_NOFRAGMENT fallback:
> 
> ...
> 
> When a promoted request takes the fallback, reset the retry counters,
> so that the fallback attempt gets a full retry budget before the OOM
> killer is considered. A request whose reclaim was not promoted spent
> its budget on the request itself and keeps its counters, as Usama Arif
> pointed out.

Thanks, I updated mm-unstable to this version.

> v3:
>  - reset the retry counters at the fallback only for requests whose
>    reclaim was promoted; a movable request already spent its budget on
>    itself (Usama Arif)

hannes's concerns/questions at
https://lore.kernel.org/20261006081050.GA234057@xxxxxxxxxxx weren't
fully addressed?  I'll add a note and await followup.

Here's how v3 altered mm.git:

 mm/page_alloc.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-make-defrag_mode-retries-follow-the-promoted-order-v3
+++ a/mm/page_alloc.c
@@ -5030,14 +5030,17 @@ retry:
 		goto retry;
 
 	/*
-	 * Reclaim/compaction failed to prevent the fallback. The retry
-	 * budget was spent on making blocks, not on the request itself;
-	 * give the fallback a fresh one before considering OOM.
+	 * Reclaim/compaction failed to prevent the fallback. A promoted
+	 * request spent its retry budget on making blocks, not on the
+	 * request itself; give its fallback a fresh one before
+	 * considering OOM.
 	 */
 	if (defrag_mode && (alloc_flags & ALLOC_NOFRAGMENT)) {
 		alloc_flags &= ~ALLOC_NOFRAGMENT;
-		no_progress_loops = 0;
-		compaction_retries = 0;
+		if (reclaim_order != order) {
+			no_progress_loops = 0;
+			compaction_retries = 0;
+		}
 		goto retry;
 	}
 
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