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

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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: Chris Li <chrisl@kernel.org>
Signed-off-by: Chris Li <chrisl@kernel.org>
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Suggested-by: Chris Li <chrisl@kernel.org>
Reviewed-by: Barry 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Kairui Song
2025-09-17 00:01:00 +08:00
committed by Andrew Morton
parent 07adc4cf1e
commit f83938e418
2 changed files with 43 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
mm/swap_table.h
View File

@@ -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

51
mm/swapfile.c
View File

@@ -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);
@@ -4072,9 +4102,10 @@ 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.
*/
swap_table_cachep = kmem_cache_create("swap_table",
sizeof(struct swap_table),
0, SLAB_PANIC | SLAB_TYPESAFE_BY_RCU, NULL);
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);
#ifdef CONFIG_MIGRATION
if (swapfile_maximum_size >= (1UL << SWP_MIG_TOTAL_BITS))