Commit 2da6de30 authored by Hugh Dickins's avatar Hugh Dickins Committed by Andrew Morton
Browse files

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/57d2eaf8-3607-f318-e0c5-be02dce61ad0@google.com


Fixes: 9a4e9f3b ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region")
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Suggested-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Keir Fraser <keirf@google.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Li Zhe <lizhe.67@bytedance.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shivank Garg <shivankg@amd.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Xu <weixugc@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: yangge <yangge1116@126.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 8d79ed36

include/linux/swap.h

+10 −0
Original line number Diff line number Diff line
@@ -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
Original line number Diff line number Diff line
@@ -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
Original line number Diff line number Diff line
@@ -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
Original line number Diff line number Diff line
@@ -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)