mm-entirely-remove-lru_add_drain-in-do_swap_page.patch removed from -mm tree

The quilt patch titled
Subject: mm: entirely remove lru_add_drain in do_swap_page
has been removed from the -mm tree. Its filename was
mm-entirely-remove-lru_add_drain-in-do_swap_page.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Barry Song (Xiaomi)" <[email protected]>
Subject: mm: entirely remove lru_add_drain in do_swap_page
Date: Thu, 2 Jul 2026 07:59:54 +0800

We are doing a lot of redundant lru_add_drain() calls in do_swap_page(), especially for synchronous I/O devices. For example, the test program below currently ends up draining lru_cache 100% of the time:

int main(int argc, char *argv[])

{
        int i;
 #define SIZE 100*1024*1024
	while(1) {
		volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE,
                        MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

		for (int i = 0; i < SIZE/sizeof(int); i++)
			p[i] =  i%64;
		madvise((void *)p, SIZE, MADV_PAGEOUT);
		for (int i = 0; i < SIZE/sizeof(int); i++)
			p[i] =  i%64;
		munmap(p, SIZE);
	}
	return 0;
}

Folio reuse now relies primarily on the exclusive hint, making lru_cache draining to drop the refcount in lru_cache largely irrelevant. For a kernel build with a minimal configuration running in a 1 GB memcg, this patch skips more than 43,000 redundant local LRU drains.

---

 mm/memory.c |   10 ----------
 1 file changed, 10 deletions(-)

@@ -4894,16 +4894,6 @@ vm_fault_t do_swap_page(struct vm_fault
 	} else if (folio != swapcache)
 		page = folio_page(folio, 0);
 
-	/*
-	 * If we want to map a page that's in the swapcache writable, we
-	 * have to detect via the refcount if we're really the exclusive
-	 * owner. Try removing the extra reference from the local LRU
-	 * caches if required.
-	 */
-	if ((vmf->flags & FAULT_FLAG_WRITE) &&
-	    !folio_test_ksm(folio) && !folio_test_lru(folio))
-		lru_add_drain();
-
 	folio_throttle_swaprate(folio, GFP_KERNEL);
 
 	/*

_

Patches currently in -mm which might be from [email protected] are

arm64-hugetlb-extend-batching-of-multiple-cont_pte-in-a-single-pte-setup.patch arm64-vmalloc-allow-arch_vmap_pte_range_map_size-to-batch-multiple-cont_pte.patch mm-vmalloc-extend-page-table-walk-to-support-larger-page_shift-sizes-and-eliminate-page-table-rewalk.patch mm-vmalloc-map-contiguous-pages-in-batches-for-vmap-if-possible.patch mm-vmalloc-align-vm_area-so-vmap-can-batch-mappings.patch