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mm, swap: simplify folio swap allocation

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With slot cache gone, clean up the allocation helpers even more. 
folio_alloc_swap will be the only entry for allocation and adding the
folio to swap cache (except suspend), making it opposite of
folio_free_swap.

Link: https://lkml.kernel.org/r/20250313165935.63303-8-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Kairui Song 2025-03-14 00:59:35 +08:00 • committed by Andrew Morton
parent 0ff67f990b
commit b487a2da35
6 changed files with 96 additions and 125 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
include/linux/swap.h
View file

@ -478,7 +478,7 @@ static inline long get_nr_swap_pages(void)
}
extern void si_swapinfo(struct sysinfo *);
swp_entry_t folio_alloc_swap(struct folio *folio);
int folio_alloc_swap(struct folio *folio, gfp_t gfp_mask);
bool folio_free_swap(struct folio *folio);
void put_swap_folio(struct folio *folio, swp_entry_t entry);
extern swp_entry_t get_swap_page_of_type(int);
@ -586,11 +586,9 @@ static inline int swp_swapcount(swp_entry_t entry)
return 0;
}
static inline swp_entry_t folio_alloc_swap(struct folio *folio)
static inline int folio_alloc_swap(struct folio *folio, gfp_t gfp_mask)
{
swp_entry_t entry;
entry.val = 0;
return entry;
return -EINVAL;
}
static inline bool folio_free_swap(struct folio *folio)

21
mm/shmem.c
View file

@ -1533,7 +1533,6 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
struct inode *inode = mapping->host;
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
swp_entry_t swap;
pgoff_t index;
int nr_pages;
bool split = false;
@ -1615,14 +1614,6 @@ try_split:
folio_mark_uptodate(folio);
}
swap = folio_alloc_swap(folio);
if (!swap.val) {
if (nr_pages > 1)
goto try_split;
goto redirty;
}
/*
* Add inode to shmem_unuse()'s list of swapped-out inodes,
* if it's not already there. Do it now before the folio is
@ -1635,20 +1626,20 @@ try_split:
if (list_empty(&info->swaplist))
list_add(&info->swaplist, &shmem_swaplist);
if (add_to_swap_cache(folio, swap,
__GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN,
NULL) == 0) {
if (!folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN)) {
shmem_recalc_inode(inode, 0, nr_pages);
swap_shmem_alloc(swap, nr_pages);
shmem_delete_from_page_cache(folio, swp_to_radix_entry(swap));
swap_shmem_alloc(folio->swap, nr_pages);
shmem_delete_from_page_cache(folio, swp_to_radix_entry(folio->swap));
mutex_unlock(&shmem_swaplist_mutex);
BUG_ON(folio_mapped(folio));
return swap_writepage(&folio->page, wbc);
}
list_del_init(&info->swaplist);
mutex_unlock(&shmem_swaplist_mutex);
put_swap_folio(folio, swap);
if (nr_pages > 1)
goto try_split;
redirty:
folio_mark_dirty(folio);
if (wbc->for_reclaim)

6
mm/swap.h
View file

@ -50,7 +50,6 @@ static inline pgoff_t swap_cache_index(swp_entry_t entry)
}
void show_swap_cache_info(void);
bool add_to_swap(struct folio *folio);
void *get_shadow_from_swap_cache(swp_entry_t entry);
int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
gfp_t gfp, void **shadowp);
@ -163,11 +162,6 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping,
return filemap_get_folio(mapping, index);
}
static inline bool add_to_swap(struct folio *folio)
{
return false;
}
static inline void *get_shadow_from_swap_cache(swp_entry_t entry)
{
return NULL;

57
mm/swap_state.c
View file

@ -166,63 +166,6 @@ void __delete_from_swap_cache(struct folio *folio,
__lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr);
}
/**
* add_to_swap - allocate swap space for a folio
* @folio: folio we want to move to swap
*
* Allocate swap space for the folio and add the folio to the
* swap cache.
*
* Context: Caller needs to hold the folio lock.
* Return: Whether the folio was added to the swap cache.
*/
bool add_to_swap(struct folio *folio)
{
swp_entry_t entry;
int err;
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
entry = folio_alloc_swap(folio);
if (!entry.val)
return false;
/*
* XArray node allocations from PF_MEMALLOC contexts could
* completely exhaust the page allocator. __GFP_NOMEMALLOC
* stops emergency reserves from being allocated.
*
* TODO: this could cause a theoretical memory reclaim
* deadlock in the swap out path.
*/
/*
* Add it to the swap cache.
*/
err = add_to_swap_cache(folio, entry,
__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
if (err)
goto fail;
/*
* Normally the folio will be dirtied in unmap because its
* pte should be dirty. A special case is MADV_FREE page. The
* page's pte could have dirty bit cleared but the folio's
* SwapBacked flag is still set because clearing the dirty bit
* and SwapBacked flag has no lock protected. For such folio,
* unmap will not set dirty bit for it, so folio reclaim will
* not write the folio out. This can cause data corruption when
* the folio is swapped in later. Always setting the dirty flag
* for the folio solves the problem.
*/
folio_mark_dirty(folio);
return true;
fail:
put_swap_folio(folio, entry);
return false;
}
/*
* This must be called only on folios that have
* been verified to be in the swap cache and locked.

113
mm/swapfile.c
View file

@ -1176,9 +1176,8 @@ static bool get_swap_device_info(struct swap_info_struct *si)
* Fast path try to get swap entries with specified order from current
* CPU's swap entry pool (a cluster).
*/
static int swap_alloc_fast(swp_entry_t *entry,
unsigned char usage,
int order)
static bool swap_alloc_fast(swp_entry_t *entry,
int order)
{
struct swap_cluster_info *ci;
struct swap_info_struct *si;
@ -1197,7 +1196,7 @@ static int swap_alloc_fast(swp_entry_t *entry,
if (cluster_is_usable(ci, order)) {
if (cluster_is_empty(ci))
offset = cluster_offset(si, ci);
found = alloc_swap_scan_cluster(si, ci, offset, order, usage);
found = alloc_swap_scan_cluster(si, ci, offset, order, SWAP_HAS_CACHE);
if (found)
*entry = swp_entry(si->type, found);
} else {
@ -1208,47 +1207,30 @@ static int swap_alloc_fast(swp_entry_t *entry,
return !!found;
}
swp_entry_t folio_alloc_swap(struct folio *folio)
/* Rotate the device and switch to a new cluster */
static bool swap_alloc_slow(swp_entry_t *entry,
int order)
{
unsigned int order = folio_order(folio);
unsigned int size = 1 << order;
struct swap_info_struct *si, *next;
swp_entry_t entry = {};
unsigned long offset;
int node;
unsigned long offset;
struct swap_info_struct *si, *next;
if (order) {
/*
* Should not even be attempting large allocations when huge
* page swap is disabled. Warn and fail the allocation.
*/
if (!IS_ENABLED(CONFIG_THP_SWAP) || size > SWAPFILE_CLUSTER) {
VM_WARN_ON_ONCE(1);
return entry;
}
}
/* Fast path using percpu cluster */
local_lock(&percpu_swap_cluster.lock);
if (swap_alloc_fast(&entry, SWAP_HAS_CACHE, order))
goto out;
/* Rotate the device and switch to a new cluster */
node = numa_node_id();
spin_lock(&swap_avail_lock);
start_over:
node = numa_node_id();
plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
/* Rotate the device and switch to a new cluster */
plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
spin_unlock(&swap_avail_lock);
if (get_swap_device_info(si)) {
offset = cluster_alloc_swap_entry(si, order, SWAP_HAS_CACHE);
put_swap_device(si);
if (offset) {
entry = swp_entry(si->type, offset);
goto out;
*entry = swp_entry(si->type, offset);
return true;
}
if (order)
goto out;
return false;
}
spin_lock(&swap_avail_lock);
@ -1267,16 +1249,67 @@ start_over:
goto start_over;
}
spin_unlock(&swap_avail_lock);
out:
local_unlock(&percpu_swap_cluster.lock);
/* Need to call this even if allocation failed, for MEMCG_SWAP_FAIL. */
if (mem_cgroup_try_charge_swap(folio, entry)) {
put_swap_folio(folio, entry);
entry.val = 0;
return false;
}
/**
* folio_alloc_swap - allocate swap space for a folio
* @folio: folio we want to move to swap
* @gfp: gfp mask for shadow nodes
*
* Allocate swap space for the folio and add the folio to the
* swap cache.
*
* Context: Caller needs to hold the folio lock.
* Return: Whether the folio was added to the swap cache.
*/
int folio_alloc_swap(struct folio *folio, gfp_t gfp)
{
unsigned int order = folio_order(folio);
unsigned int size = 1 << order;
swp_entry_t entry = {};
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
/*
* Should not even be attempting large allocations when huge
* page swap is disabled. Warn and fail the allocation.
*/
if (order && (!IS_ENABLED(CONFIG_THP_SWAP) || size > SWAPFILE_CLUSTER)) {
VM_WARN_ON_ONCE(1);
return -EINVAL;
}
if (entry.val)
atomic_long_sub(size, &nr_swap_pages);
return entry;
local_lock(&percpu_swap_cluster.lock);
if (!swap_alloc_fast(&entry, order))
swap_alloc_slow(&entry, order);
local_unlock(&percpu_swap_cluster.lock);
/* Need to call this even if allocation failed, for MEMCG_SWAP_FAIL. */
if (mem_cgroup_try_charge_swap(folio, entry))
goto out_free;
if (!entry.val)
return -ENOMEM;
/*
* XArray node allocations from PF_MEMALLOC contexts could
* completely exhaust the page allocator. __GFP_NOMEMALLOC
* stops emergency reserves from being allocated.
*
* TODO: this could cause a theoretical memory reclaim
* deadlock in the swap out path.
*/
if (add_to_swap_cache(folio, entry, gfp | __GFP_NOMEMALLOC, NULL))
goto out_free;
atomic_long_sub(size, &nr_swap_pages);
return 0;
out_free:
put_swap_folio(folio, entry);
return -ENOMEM;
}
static struct swap_info_struct *_swap_info_get(swp_entry_t entry)

16
mm/vmscan.c
View file

@ -1289,7 +1289,7 @@ retry:
split_folio_to_list(folio, folio_list))
goto activate_locked;
}
if (!add_to_swap(folio)) {
if (folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOWARN)) {
int __maybe_unused order = folio_order(folio);
if (!folio_test_large(folio))
@ -1305,9 +1305,21 @@ retry:
}
#endif
count_mthp_stat(order, MTHP_STAT_SWPOUT_FALLBACK);
if (!add_to_swap(folio))
if (folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOWARN))
goto activate_locked_split;
}
/*
* Normally the folio will be dirtied in unmap because its
* pte should be dirty. A special case is MADV_FREE page. The
* page's pte could have dirty bit cleared but the folio's
* SwapBacked flag is still set because clearing the dirty bit
* and SwapBacked flag has no lock protected. For such folio,
* unmap will not set dirty bit for it, so folio reclaim will
* not write the folio out. This can cause data corruption when
* the folio is swapped in later. Always setting the dirty flag
* for the folio solves the problem.
*/
folio_mark_dirty(folio);
}
}