Re: [PATCH 1/1] mm: swap: add nr argument in swapcache_prepare and swapcache_clear to support large folios
From: Baolin Wang
Date: Tue Jul 30 2024 - 04:20:58 EST
On 2024/7/30 15:13, Barry Song wrote:
From: Barry Song <v-songbaohua@xxxxxxxx>
Right now, swapcache_prepare() and swapcache_clear() supports one entry
only, to support large folios, we need to handle multiple swap entries.
To optimize stack usage, we iterate twice in __swap_duplicate(): the
first time to verify that all entries are valid, and the second time
to apply the modifications to the entries.
Currently, we're using nr=1 for the existing users.
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Thanks Barry. Tested it with my shmem swap patches, and works well. So
Tested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
include/linux/swap.h | 4 +-
mm/memory.c | 6 +--
mm/swap.h | 5 ++-
mm/swap_state.c | 2 +-
mm/swapfile.c | 101 +++++++++++++++++++++++++------------------
5 files changed, 68 insertions(+), 50 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index ba7ea95d1c57..5b920fa2315b 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(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(swp_entry_t swp, int nr)
{
return 0;
}
diff --git a/mm/memory.c b/mm/memory.c
index 833d2cad6eb2..b8675617a5e3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4081,7 +4081,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
* reusing the same entry. It's undetectable as
* pte_same() returns true due to entry reuse.
*/
- if (swapcache_prepare(entry)) {
+ if (swapcache_prepare(entry, 1)) {
/* Relax a bit to prevent rapid repeated page faults */
schedule_timeout_uninterruptible(1);
goto out;
@@ -4387,7 +4387,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
out:
/* Clear the swap cache pin for direct swapin after PTL unlock */
if (need_clear_cache)
- swapcache_clear(si, entry);
+ swapcache_clear(si, entry, 1);
if (si)
put_swap_device(si);
return ret;
@@ -4403,7 +4403,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
folio_put(swapcache);
}
if (need_clear_cache)
- swapcache_clear(si, entry);
+ swapcache_clear(si, entry, 1);
if (si)
put_swap_device(si);
return ret;
diff --git a/mm/swap.h b/mm/swap.h
index baa1fa946b34..7c6330561d84 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(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(struct swap_info_struct *si, swp_entry_t entry, int nr)
{
}
@@ -172,4 +172,5 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
return 0;
}
#endif /* CONFIG_SWAP */
+
#endif /* _MM_SWAP_H */
diff --git a/mm/swap_state.c b/mm/swap_state.c
index a1726e49a5eb..b06f2a054f5a 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -477,7 +477,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
/*
* Swap entry may have been freed since our caller observed it.
*/
- err = swapcache_prepare(entry);
+ err = swapcache_prepare(entry, 1);
if (!err)
break;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5f73a8553371..757d38a86f56 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
@@ -3373,60 +3373,77 @@ 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(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);
@@ -3439,7 +3456,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
*/
void swap_shmem_alloc(swp_entry_t entry)
{
- __swap_duplicate(entry, SWAP_MAP_SHMEM);
+ __swap_duplicate(entry, SWAP_MAP_SHMEM, 1);
}
/*
@@ -3453,29 +3470,29 @@ int swap_duplicate(swp_entry_t entry)
{
int err = 0;
- while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
+ while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM)
err = add_swap_count_continuation(entry, GFP_ATOMIC);
return err;
}
/*
- * @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(swp_entry_t entry, int nr)
{
- return __swap_duplicate(entry, SWAP_HAS_CACHE);
+ return __swap_duplicate(entry, SWAP_HAS_CACHE, nr);
}
-void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
+void swapcache_clear(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)