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FAILED: patch "[PATCH] mm: folio_may_be_lru_cached() unless folio_test_large()" failed to apply to 6.6-stable tree

PATCH [email protected] 1 participant 1 message Sep 21, 2025

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Stable branch Memory management Memory mapping MM swap +1 more subsystems
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The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025092143-defrost-backboned-d1ea@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <[email protected]>
Date: Mon, 8 Sep 2025 15:23:15 -0700
Subject: [PATCH] mm: folio_may_be_lru_cached() unless folio_test_large()

mm/swap.c and mm/mlock.c agree to drain any per-CPU batch as soon as a large folio is added: so collect_longterm_unpinnable_folios() just wastes effort when calling lru_add_drain[_all]() on a large folio.

But although there is good reason not to batch up PMD-sized folios, we might well benefit from batching a small number of low-order mTHPs (though unclear how that "small number" limitation will be implemented).

So ask if folio_may_be_lru_cached() rather than !folio_test_large(), to insulate those particular checks from future change. Name preferred to "folio_is_batchable" because large folios can well be put on a batch: it's just the per-CPU LRU caches, drained much later, which need care.

Marked for stable, to counter the increase in lru_add_drain_all()s from "mm/gup: check ref_count instead of lru before migration".

Link https://lkml.kernel.org/r/[email protected] open here
Fixes 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region")
Signed-off-by Hugh Dickins <[email protected]>
Suggested-by David Hildenbrand <[email protected]>
Acked-by David Hildenbrand <[email protected]>
Cc "Aneesh Kumar K.V" <[email protected]>
Cc Axel Rasmussen <[email protected]>
Cc Chris Li <[email protected]>
Cc Christoph Hellwig <[email protected]>
Cc Jason Gunthorpe <[email protected]>
Cc Johannes Weiner <[email protected]>
Cc John Hubbard <[email protected]>
Cc Keir Fraser <[email protected]>
Cc Konstantin Khlebnikov <[email protected]>
Cc Li Zhe <[email protected]>
Cc Matthew Wilcox (Oracle) <[email protected]>
Cc Peter Xu <[email protected]>
Cc Rik van Riel <[email protected]>
Cc Shivank Garg <[email protected]>
Cc Vlastimil Babka <[email protected]>
Cc Wei Xu <[email protected]>
Cc Will Deacon <[email protected]>
Cc yangge <[email protected]>
Cc Yuanchu Xie <[email protected]>
Cc Yu Zhao <[email protected]>
Cc <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
include/linux/swap.h +10 -0
index 2fe6ed2cc3fd..7012a0f758d8 100644
@@ -385,6 +385,16 @@ void folio_add_lru_vma(struct folio *, struct vm_area_struct *);
 void mark_page_accessed(struct page *);
 void folio_mark_accessed(struct folio *);
 
+static inline bool folio_may_be_lru_cached(struct folio *folio)
+{
+	/*
+	 * Holding PMD-sized folios in per-CPU LRU cache unbalances accounting.
+	 * Holding small numbers of low-order mTHP folios in per-CPU LRU cache
+	 * will be sensible, but nobody has implemented and tested that yet.
+	 */
+	return !folio_test_large(folio);
+}
+
 extern atomic_t lru_disable_count;
 
 static inline bool lru_cache_disabled(void)
mm/gup.c +2 -2
index b47066a54f52..0bc4d140fc07 100644
@@ -2307,13 +2307,13 @@ static unsigned long collect_longterm_unpinnable_folios(
 			continue;
 		}
 
-		if (drained == 0 &&
+		if (drained == 0 && folio_may_be_lru_cached(folio) &&
 				folio_ref_count(folio) !=
 				folio_expected_ref_count(folio) + 1) {
 			lru_add_drain();
 			drained = 1;
 		}
-		if (drained == 1 &&
+		if (drained == 1 && folio_may_be_lru_cached(folio) &&
 				folio_ref_count(folio) !=
 				folio_expected_ref_count(folio) + 1) {
 			lru_add_drain_all();
mm/mlock.c +3 -3
index a1d93ad33c6d..bb0776f5ef7c 100644
@@ -255,7 +255,7 @@ void mlock_folio(struct folio *folio)
 
 	folio_get(folio);
 	if (!folio_batch_add(fbatch, mlock_lru(folio)) ||
-	    folio_test_large(folio) || lru_cache_disabled())
+	    !folio_may_be_lru_cached(folio) || lru_cache_disabled())
 		mlock_folio_batch(fbatch);
 	local_unlock(&mlock_fbatch.lock);
 }

@@ -278,7 +278,7 @@ void mlock_new_folio(struct folio *folio)
 
 	folio_get(folio);
 	if (!folio_batch_add(fbatch, mlock_new(folio)) ||
-	    folio_test_large(folio) || lru_cache_disabled())
+	    !folio_may_be_lru_cached(folio) || lru_cache_disabled())
 		mlock_folio_batch(fbatch);
 	local_unlock(&mlock_fbatch.lock);
 }

@@ -299,7 +299,7 @@ void munlock_folio(struct folio *folio)
 	 */
 	folio_get(folio);
 	if (!folio_batch_add(fbatch, folio) ||
-	    folio_test_large(folio) || lru_cache_disabled())
+	    !folio_may_be_lru_cached(folio) || lru_cache_disabled())
 		mlock_folio_batch(fbatch);
 	local_unlock(&mlock_fbatch.lock);
 }
mm/swap.c +1 -1
index 6ae2d5680574..b74ebe865dd9 100644
@@ -192,7 +192,7 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch,
 		local_lock(&cpu_fbatches.lock);
 
 	if (!folio_batch_add(this_cpu_ptr(fbatch), folio) ||
-			folio_test_large(folio) || lru_cache_disabled())
+			!folio_may_be_lru_cached(folio) || lru_cache_disabled())
 		folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn);
 
 	if (disable_irq)