Commit f83938e4 authored by Kairui Song's avatar Kairui Song Committed by Andrew Morton
Browse files

mm, swap: use a single page for swap table when the size fits 

We have a cluster size of 512 slots.  Each slot consumes 8 bytes in swap
table so the swap table size of each cluster is exactly one page (4K).

If that condition is true, allocate one page direct and disable the slab
cache to reduce the memory usage of swap table and avoid fragmentation.

Link: https://lkml.kernel.org/r/20250916160100.31545-16-ryncsn@gmail.com


Co-developed-by: default avatarChris Li <chrisl@kernel.org>
Signed-off-by: default avatarChris Li <chrisl@kernel.org>
Signed-off-by: default avatarKairui Song <kasong@tencent.com>
Acked-by: default avatarChris Li <chrisl@kernel.org>
Suggested-by: default avatarChris Li <chrisl@kernel.org>
Reviewed-by: default avatarBarry Song <baohua@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: kernel test robot <oliver.sang@intel.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 07adc4cf

mm/swap_table.h

+2 −0
Original line number Diff line number Diff line
@@ -11,6 +11,8 @@ struct swap_table { 
	atomic_long_t entries[SWAPFILE_CLUSTER];

};



#define SWP_TABLE_USE_PAGE (sizeof(struct swap_table) == PAGE_SIZE)



/*

 * A swap table entry represents the status of a swap slot on a swap

 * (physical or virtual) device. The swap table in each cluster is a

mm/swapfile.c

+41 −10
Original line number Diff line number Diff line
@@ -434,6 +434,38 @@ static inline unsigned int cluster_offset(struct swap_info_struct *si, 
	return cluster_index(si, ci) * SWAPFILE_CLUSTER;

}



static struct swap_table *swap_table_alloc(gfp_t gfp)

{

	struct folio *folio;



	if (!SWP_TABLE_USE_PAGE)

		return kmem_cache_zalloc(swap_table_cachep, gfp);



	folio = folio_alloc(gfp | __GFP_ZERO, 0);

	if (folio)

		return folio_address(folio);

	return NULL;

}



static void swap_table_free_folio_rcu_cb(struct rcu_head *head)

{

	struct folio *folio;



	folio = page_folio(container_of(head, struct page, rcu_head));

	folio_put(folio);

}



static void swap_table_free(struct swap_table *table)

{

	if (!SWP_TABLE_USE_PAGE) {

		kmem_cache_free(swap_table_cachep, table);

		return;

	}



	call_rcu(&(folio_page(virt_to_folio(table), 0)->rcu_head),

		 swap_table_free_folio_rcu_cb);

}



static void swap_cluster_free_table(struct swap_cluster_info *ci)

{

	unsigned int ci_off;
@@ -447,7 +479,7 @@ static void swap_cluster_free_table(struct swap_cluster_info *ci) 
	table = (void *)rcu_dereference_protected(ci->table, true);

	rcu_assign_pointer(ci->table, NULL);



	kmem_cache_free(swap_table_cachep, table);

	swap_table_free(table);

}



/*
@@ -470,8 +502,7 @@ swap_cluster_alloc_table(struct swap_info_struct *si, 
	/* The cluster must be free and was just isolated from the free list. */

	VM_WARN_ON_ONCE(ci->flags || !cluster_is_empty(ci));



	table = kmem_cache_zalloc(swap_table_cachep,

				  __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN);

	table = swap_table_alloc(__GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN);

	if (table) {

		rcu_assign_pointer(ci->table, table);

		return ci;
@@ -487,8 +518,7 @@ swap_cluster_alloc_table(struct swap_info_struct *si, 
		spin_unlock(&si->global_cluster_lock);

	local_unlock(&percpu_swap_cluster.lock);



	table = kmem_cache_zalloc(swap_table_cachep,

				  __GFP_HIGH | __GFP_NOMEMALLOC | GFP_KERNEL);

	table = swap_table_alloc(__GFP_HIGH | __GFP_NOMEMALLOC | GFP_KERNEL);



	/*

	 * Back to atomic context. We might have migrated to a new CPU with a
@@ -506,7 +536,7 @@ swap_cluster_alloc_table(struct swap_info_struct *si, 
	/* Nothing except this helper should touch a dangling empty cluster. */

	if (WARN_ON_ONCE(cluster_table_is_alloced(ci))) {

		if (table)

			kmem_cache_free(swap_table_cachep, table);

			swap_table_free(table);

		return ci;

	}
@@ -734,7 +764,7 @@ static int inc_cluster_info_page(struct swap_info_struct *si, 


	ci = cluster_info + idx;

	if (!ci->table) {

		table = kmem_cache_zalloc(swap_table_cachep, GFP_KERNEL);

		table = swap_table_alloc(GFP_KERNEL);

		if (!table)

			return -ENOMEM;

		rcu_assign_pointer(ci->table, table);
@@ -4072,6 +4102,7 @@ static int __init swapfile_init(void) 
	 * only, and all swap cache readers (swap_cache_*) verifies

	 * the content before use. So it's safe to use RCU slab here.

	 */

	if (!SWP_TABLE_USE_PAGE)

		swap_table_cachep = kmem_cache_create("swap_table",

				    sizeof(struct swap_table),

				    0, SLAB_PANIC | SLAB_TYPESAFE_BY_RCU, NULL);