[PATCH v5 1/4] mm: swap: introduce swapcache_prepare_nr and swapcache_clear_nr for large folios swap-in
From: Barry Song
Date: Fri Jul 26 2024 - 05:47:25 EST
From: Barry Song <v-songbaohua@xxxxxxxx>
Commit 13ddaf26be32 ("mm/swap: fix race when skipping swapcache") supports
one entry only, to support large folio swap-in, we need to handle multiple
swap entries.
To optimize stack usage, we iterate twice in __swap_duplicate_nr(): the
first time to verify that all entries are valid, and the second time to
apply the modifications to the entries.
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
include/linux/swap.h | 9 +++-
mm/swap.h | 10 ++++-
mm/swapfile.c | 102 ++++++++++++++++++++++++++-----------------
3 files changed, 77 insertions(+), 44 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index ba7ea95d1c57..f1b28fd04533 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -480,7 +480,7 @@ extern int get_swap_pages(int n, swp_entry_t swp_entries[], int order);
extern int add_swap_count_continuation(swp_entry_t, gfp_t);
extern void swap_shmem_alloc(swp_entry_t);
extern int swap_duplicate(swp_entry_t);
-extern int swapcache_prepare(swp_entry_t);
+extern int swapcache_prepare_nr(swp_entry_t entry, int nr);
extern void swap_free_nr(swp_entry_t entry, int nr_pages);
extern void swapcache_free_entries(swp_entry_t *entries, int n);
extern void free_swap_and_cache_nr(swp_entry_t entry, int nr);
@@ -554,7 +554,7 @@ static inline int swap_duplicate(swp_entry_t swp)
return 0;
}
-static inline int swapcache_prepare(swp_entry_t swp)
+static inline int swapcache_prepare_nr(swp_entry_t swp, int nr)
{
return 0;
}
@@ -612,6 +612,11 @@ static inline void swap_free(swp_entry_t entry)
swap_free_nr(entry, 1);
}
+static inline int swapcache_prepare(swp_entry_t entry)
+{
+ return swapcache_prepare_nr(entry, 1);
+}
+
#ifdef CONFIG_MEMCG
static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
diff --git a/mm/swap.h b/mm/swap.h
index baa1fa946b34..81ff7eb0be9c 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -59,7 +59,7 @@ void __delete_from_swap_cache(struct folio *folio,
void delete_from_swap_cache(struct folio *folio);
void clear_shadow_from_swap_cache(int type, unsigned long begin,
unsigned long end);
-void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry);
+void swapcache_clear_nr(struct swap_info_struct *si, swp_entry_t entry, int nr);
struct folio *swap_cache_get_folio(swp_entry_t entry,
struct vm_area_struct *vma, unsigned long addr);
struct folio *filemap_get_incore_folio(struct address_space *mapping,
@@ -120,7 +120,7 @@ static inline int swap_writepage(struct page *p, struct writeback_control *wbc)
return 0;
}
-static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
+static inline void swapcache_clear_nr(struct swap_info_struct *si, swp_entry_t entry, int nr)
{
}
@@ -172,4 +172,10 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
return 0;
}
#endif /* CONFIG_SWAP */
+
+static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
+{
+ swapcache_clear_nr(si, entry, 1);
+}
+
#endif /* _MM_SWAP_H */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5f73a8553371..e688e46f1c62 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3363,7 +3363,7 @@ void si_swapinfo(struct sysinfo *val)
}
/*
- * Verify that a swap entry is valid and increment its swap map count.
+ * Verify that nr swap entries are valid and increment their swap map counts.
*
* Returns error code in following case.
* - success -> 0
@@ -3373,66 +3373,88 @@ void si_swapinfo(struct sysinfo *val)
* - swap-cache reference is requested but the entry is not used. -> ENOENT
* - swap-mapped reference requested but needs continued swap count. -> ENOMEM
*/
-static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
+static int __swap_duplicate_nr(swp_entry_t entry, unsigned char usage, int nr)
{
struct swap_info_struct *p;
struct swap_cluster_info *ci;
unsigned long offset;
unsigned char count;
unsigned char has_cache;
- int err;
+ int err, i;
p = swp_swap_info(entry);
offset = swp_offset(entry);
+ VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
ci = lock_cluster_or_swap_info(p, offset);
- count = p->swap_map[offset];
+ err = 0;
+ for (i = 0; i < nr; i++) {
+ count = p->swap_map[offset + i];
- /*
- * swapin_readahead() doesn't check if a swap entry is valid, so the
- * swap entry could be SWAP_MAP_BAD. Check here with lock held.
- */
- if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
- err = -ENOENT;
- goto unlock_out;
- }
+ /*
+ * swapin_readahead() doesn't check if a swap entry is valid, so the
+ * swap entry could be SWAP_MAP_BAD. Check here with lock held.
+ */
+ if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
+ err = -ENOENT;
+ goto unlock_out;
+ }
- has_cache = count & SWAP_HAS_CACHE;
- count &= ~SWAP_HAS_CACHE;
- err = 0;
+ has_cache = count & SWAP_HAS_CACHE;
+ count &= ~SWAP_HAS_CACHE;
- if (usage == SWAP_HAS_CACHE) {
+ if (usage == SWAP_HAS_CACHE) {
+ /* set SWAP_HAS_CACHE if there is no cache and entry is used */
+ if (!has_cache && count)
+ continue;
+ else if (has_cache) /* someone else added cache */
+ err = -EEXIST;
+ else /* no users remaining */
+ err = -ENOENT;
- /* set SWAP_HAS_CACHE if there is no cache and entry is used */
- if (!has_cache && count)
- has_cache = SWAP_HAS_CACHE;
- else if (has_cache) /* someone else added cache */
- err = -EEXIST;
- else /* no users remaining */
- err = -ENOENT;
+ } else if (count || has_cache) {
- } else if (count || has_cache) {
+ if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
+ continue;
+ else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
+ err = -EINVAL;
+ else if (swap_count_continued(p, offset + i, count))
+ continue;
+ else
+ err = -ENOMEM;
+ } else
+ err = -ENOENT; /* unused swap entry */
- if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
+ if (err)
+ goto unlock_out;
+ }
+
+ for (i = 0; i < nr; i++) {
+ count = p->swap_map[offset + i];
+ has_cache = count & SWAP_HAS_CACHE;
+ count &= ~SWAP_HAS_CACHE;
+
+ if (usage == SWAP_HAS_CACHE)
+ has_cache = SWAP_HAS_CACHE;
+ else if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
count += usage;
- else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
- err = -EINVAL;
- else if (swap_count_continued(p, offset, count))
- count = COUNT_CONTINUED;
else
- err = -ENOMEM;
- } else
- err = -ENOENT; /* unused swap entry */
+ count = COUNT_CONTINUED;
- if (!err)
- WRITE_ONCE(p->swap_map[offset], count | has_cache);
+ WRITE_ONCE(p->swap_map[offset + i], count | has_cache);
+ }
unlock_out:
unlock_cluster_or_swap_info(p, ci);
return err;
}
+static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
+{
+ return __swap_duplicate_nr(entry, usage, 1);
+}
+
/*
* Help swapoff by noting that swap entry belongs to shmem/tmpfs
* (in which case its reference count is never incremented).
@@ -3459,23 +3481,23 @@ int swap_duplicate(swp_entry_t entry)
}
/*
- * @entry: swap entry for which we allocate swap cache.
+ * @entry: first swap entry from which we allocate nr swap cache.
*
- * Called when allocating swap cache for existing swap entry,
+ * Called when allocating swap cache for existing swap entries,
* This can return error codes. Returns 0 at success.
* -EEXIST means there is a swap cache.
* Note: return code is different from swap_duplicate().
*/
-int swapcache_prepare(swp_entry_t entry)
+int swapcache_prepare_nr(swp_entry_t entry, int nr)
{
- return __swap_duplicate(entry, SWAP_HAS_CACHE);
+ return __swap_duplicate_nr(entry, SWAP_HAS_CACHE, nr);
}
-void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
+void swapcache_clear_nr(struct swap_info_struct *si, swp_entry_t entry, int nr)
{
unsigned long offset = swp_offset(entry);
- cluster_swap_free_nr(si, offset, 1, SWAP_HAS_CACHE);
+ cluster_swap_free_nr(si, offset, nr, SWAP_HAS_CACHE);
}
struct swap_info_struct *swp_swap_info(swp_entry_t entry)
--
2.34.1