As all callers of swap_entry_range_free() have already ensured slots to
be freed are marked as SWAP_HAS_CACHE while holding the cluster lock,
the BUG_ON check can be safely removed. After this, the function
swap_entry_range_free() could drop any kind of last flag, rename it to
swap_entries_free() and update it's comment accordingly.
This is a preparation to use swap_entries_free() to drop last ref count
and SWAP_MAP_SHMEM flag.
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
---
mm/swapfile.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5a775456e26c..0aa7ce82c013 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -52,9 +52,9 @@
static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
unsigned char);
static void free_swap_count_continuations(struct swap_info_struct *);
-static void swap_entry_range_free(struct swap_info_struct *si,
- struct swap_cluster_info *ci,
- swp_entry_t entry, unsigned int nr_pages);
+static void swap_entries_free(struct swap_info_struct *si,
+ struct swap_cluster_info *ci,
+ swp_entry_t entry, unsigned int nr_pages);
static void swap_range_alloc(struct swap_info_struct *si,
unsigned int nr_entries);
static bool folio_swapcache_freeable(struct folio *folio);
@@ -1463,7 +1463,7 @@ static unsigned char swap_entry_put(struct swap_info_struct *si,
ci = lock_cluster(si, offset);
usage = swap_entry_put_locked(si, offset, 1);
if (!usage)
- swap_entry_range_free(si, ci, swp_entry(si->type, offset), 1);
+ swap_entries_free(si, ci, swp_entry(si->type, offset), 1);
unlock_cluster(ci);
return usage;
@@ -1493,7 +1493,7 @@ static bool swap_entries_put_nr(struct swap_info_struct *si,
for (i = 0; i < nr; i++)
WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
if (!has_cache)
- swap_entry_range_free(si, ci, entry, nr);
+ swap_entries_free(si, ci, entry, nr);
unlock_cluster(ci);
return has_cache;
@@ -1512,12 +1512,12 @@ static bool swap_entries_put_nr(struct swap_info_struct *si,
}
/*
- * Drop the last HAS_CACHE flag of swap entries, caller have to
- * ensure all entries belong to the same cgroup.
+ * Drop the last flag(1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM) of swap entries,
+ * caller have to ensure all entries belong to the same cgroup and cluster.
*/
-static void swap_entry_range_free(struct swap_info_struct *si,
- struct swap_cluster_info *ci,
- swp_entry_t entry, unsigned int nr_pages)
+static void swap_entries_free(struct swap_info_struct *si,
+ struct swap_cluster_info *ci,
+ swp_entry_t entry, unsigned int nr_pages)
{
unsigned long offset = swp_offset(entry);
unsigned char *map = si->swap_map + offset;
@@ -1530,7 +1530,6 @@ static void swap_entry_range_free(struct swap_info_struct *si,
ci->count -= nr_pages;
do {
- VM_BUG_ON(*map != SWAP_HAS_CACHE);
*map = 0;
} while (++map < map_end);
@@ -1553,7 +1552,7 @@ static void cluster_swap_free_nr(struct swap_info_struct *si,
ci = lock_cluster(si, offset);
do {
if (!swap_entry_put_locked(si, offset, usage))
- swap_entry_range_free(si, ci, swp_entry(si->type, offset), 1);
+ swap_entries_free(si, ci, swp_entry(si->type, offset), 1);
} while (++offset < end);
unlock_cluster(ci);
}
@@ -1596,11 +1595,11 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
ci = lock_cluster(si, offset);
if (swap_only_has_cache(si, offset, size))
- swap_entry_range_free(si, ci, entry, size);
+ swap_entries_free(si, ci, entry, size);
else {
for (int i = 0; i < size; i++, entry.val++) {
if (!swap_entry_put_locked(si, offset + i, SWAP_HAS_CACHE))
- swap_entry_range_free(si, ci, entry, 1);
+ swap_entries_free(si, ci, entry, 1);
}
}
unlock_cluster(ci);
--
2.30.0On Tue, Mar 18, 2025 at 2:10 PM Kemeng Shi <shikemeng@huaweicloud.com> wrote:
>
> As all callers of swap_entry_range_free() have already ensured slots to
> be freed are marked as SWAP_HAS_CACHE while holding the cluster lock,
> the BUG_ON check can be safely removed. After this, the function
> swap_entry_range_free() could drop any kind of last flag, rename it to
> swap_entries_free() and update it's comment accordingly.
>
> This is a preparation to use swap_entries_free() to drop last ref count
> and SWAP_MAP_SHMEM flag.
>
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
> ---
> mm/swapfile.c | 27 +++++++++++++--------------
> 1 file changed, 13 insertions(+), 14 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 5a775456e26c..0aa7ce82c013 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -52,9 +52,9 @@
> static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
> unsigned char);
> static void free_swap_count_continuations(struct swap_info_struct *);
> -static void swap_entry_range_free(struct swap_info_struct *si,
> - struct swap_cluster_info *ci,
> - swp_entry_t entry, unsigned int nr_pages);
> +static void swap_entries_free(struct swap_info_struct *si,
> + struct swap_cluster_info *ci,
> + swp_entry_t entry, unsigned int nr_pages);
> static void swap_range_alloc(struct swap_info_struct *si,
> unsigned int nr_entries);
> static bool folio_swapcache_freeable(struct folio *folio);
> @@ -1463,7 +1463,7 @@ static unsigned char swap_entry_put(struct swap_info_struct *si,
> ci = lock_cluster(si, offset);
> usage = swap_entry_put_locked(si, offset, 1);
> if (!usage)
> - swap_entry_range_free(si, ci, swp_entry(si->type, offset), 1);
> + swap_entries_free(si, ci, swp_entry(si->type, offset), 1);
> unlock_cluster(ci);
>
> return usage;
> @@ -1493,7 +1493,7 @@ static bool swap_entries_put_nr(struct swap_info_struct *si,
> for (i = 0; i < nr; i++)
> WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
> if (!has_cache)
> - swap_entry_range_free(si, ci, entry, nr);
> + swap_entries_free(si, ci, entry, nr);
> unlock_cluster(ci);
>
> return has_cache;
> @@ -1512,12 +1512,12 @@ static bool swap_entries_put_nr(struct swap_info_struct *si,
> }
>
> /*
> - * Drop the last HAS_CACHE flag of swap entries, caller have to
> - * ensure all entries belong to the same cgroup.
> + * Drop the last flag(1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM) of swap entries,
> + * caller have to ensure all entries belong to the same cgroup and cluster.
> */
> -static void swap_entry_range_free(struct swap_info_struct *si,
> - struct swap_cluster_info *ci,
> - swp_entry_t entry, unsigned int nr_pages)
> +static void swap_entries_free(struct swap_info_struct *si,
> + struct swap_cluster_info *ci,
> + swp_entry_t entry, unsigned int nr_pages)
> {
> unsigned long offset = swp_offset(entry);
> unsigned char *map = si->swap_map + offset;
> @@ -1530,7 +1530,6 @@ static void swap_entry_range_free(struct swap_info_struct *si,
>
> ci->count -= nr_pages;
> do {
> - VM_BUG_ON(*map != SWAP_HAS_CACHE);
Hi Kemeng
Instead of just dropping this check, maybe it's better to change it to
something like VM_BUG_ON(!*map); to catch potential SWAP double free?
I've found this check very helpful for debugging, especially for
catching concurrency problems.
Or more strictly: VM_BUG_ON(*map != SWAP_HAS_CACHE && *map != 1 &&
*map != SWAP_MAP_SHMEM);, you may introduce a helper to check if a
entry is the "last map" like this and use it somewhere else too.
> *map = 0;
> } while (++map < map_end);
>
> @@ -1553,7 +1552,7 @@ static void cluster_swap_free_nr(struct swap_info_struct *si,
> ci = lock_cluster(si, offset);
> do {
> if (!swap_entry_put_locked(si, offset, usage))
> - swap_entry_range_free(si, ci, swp_entry(si->type, offset), 1);
> + swap_entries_free(si, ci, swp_entry(si->type, offset), 1);
> } while (++offset < end);
> unlock_cluster(ci);
> }
> @@ -1596,11 +1595,11 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
>
> ci = lock_cluster(si, offset);
> if (swap_only_has_cache(si, offset, size))
> - swap_entry_range_free(si, ci, entry, size);
> + swap_entries_free(si, ci, entry, size);
> else {
> for (int i = 0; i < size; i++, entry.val++) {
> if (!swap_entry_put_locked(si, offset + i, SWAP_HAS_CACHE))
> - swap_entry_range_free(si, ci, entry, 1);
> + swap_entries_free(si, ci, entry, 1);
> }
> }
> unlock_cluster(ci);
> --
> 2.30.0
>
on 3/19/2025 1:18 PM, Kairui Song wrote:
> On Tue, Mar 18, 2025 at 2:10 PM Kemeng Shi <shikemeng@huaweicloud.com> wrote:
>>
>> As all callers of swap_entry_range_free() have already ensured slots to
>> be freed are marked as SWAP_HAS_CACHE while holding the cluster lock,
>> the BUG_ON check can be safely removed. After this, the function
>> swap_entry_range_free() could drop any kind of last flag, rename it to
>> swap_entries_free() and update it's comment accordingly.
>>
>> This is a preparation to use swap_entries_free() to drop last ref count
>> and SWAP_MAP_SHMEM flag.
>>
>> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
>> Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
>> ---
>> mm/swapfile.c | 27 +++++++++++++--------------
>> 1 file changed, 13 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 5a775456e26c..0aa7ce82c013 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -52,9 +52,9 @@
>> static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
>> unsigned char);
>> static void free_swap_count_continuations(struct swap_info_struct *);
>> -static void swap_entry_range_free(struct swap_info_struct *si,
>> - struct swap_cluster_info *ci,
>> - swp_entry_t entry, unsigned int nr_pages);
>> +static void swap_entries_free(struct swap_info_struct *si,
>> + struct swap_cluster_info *ci,
>> + swp_entry_t entry, unsigned int nr_pages);
>> static void swap_range_alloc(struct swap_info_struct *si,
>> unsigned int nr_entries);
>> static bool folio_swapcache_freeable(struct folio *folio);
>> @@ -1463,7 +1463,7 @@ static unsigned char swap_entry_put(struct swap_info_struct *si,
>> ci = lock_cluster(si, offset);
>> usage = swap_entry_put_locked(si, offset, 1);
>> if (!usage)
>> - swap_entry_range_free(si, ci, swp_entry(si->type, offset), 1);
>> + swap_entries_free(si, ci, swp_entry(si->type, offset), 1);
>> unlock_cluster(ci);
>>
>> return usage;
>> @@ -1493,7 +1493,7 @@ static bool swap_entries_put_nr(struct swap_info_struct *si,
>> for (i = 0; i < nr; i++)
>> WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
>> if (!has_cache)
>> - swap_entry_range_free(si, ci, entry, nr);
>> + swap_entries_free(si, ci, entry, nr);
>> unlock_cluster(ci);
>>
>> return has_cache;
>> @@ -1512,12 +1512,12 @@ static bool swap_entries_put_nr(struct swap_info_struct *si,
>> }
>>
>> /*
>> - * Drop the last HAS_CACHE flag of swap entries, caller have to
>> - * ensure all entries belong to the same cgroup.
>> + * Drop the last flag(1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM) of swap entries,
>> + * caller have to ensure all entries belong to the same cgroup and cluster.
>> */
>> -static void swap_entry_range_free(struct swap_info_struct *si,
>> - struct swap_cluster_info *ci,
>> - swp_entry_t entry, unsigned int nr_pages)
>> +static void swap_entries_free(struct swap_info_struct *si,
>> + struct swap_cluster_info *ci,
>> + swp_entry_t entry, unsigned int nr_pages)
>> {
>> unsigned long offset = swp_offset(entry);
>> unsigned char *map = si->swap_map + offset;
>> @@ -1530,7 +1530,6 @@ static void swap_entry_range_free(struct swap_info_struct *si,
>>
>> ci->count -= nr_pages;
>> do {
>> - VM_BUG_ON(*map != SWAP_HAS_CACHE);
>
> Hi Kemeng
>
> Instead of just dropping this check, maybe it's better to change it to
> something like VM_BUG_ON(!*map); to catch potential SWAP double free?
> I've found this check very helpful for debugging, especially for
> catching concurrency problems.
Sure, will keep VM_BUG_ON as it's useful.
>
> Or more strictly: VM_BUG_ON(*map != SWAP_HAS_CACHE && *map != 1 &&
> *map != SWAP_MAP_SHMEM);, you may introduce a helper to check if a
> entry is the "last map" like this and use it somewhere else too.
I'd add VM_BUG_ON in this way to catch unexpected freeing.
Thanks,
Kemeng
>
>
>> *map = 0;
>> } while (++map < map_end);
>>
>> @@ -1553,7 +1552,7 @@ static void cluster_swap_free_nr(struct swap_info_struct *si,
>> ci = lock_cluster(si, offset);
>> do {
>> if (!swap_entry_put_locked(si, offset, usage))
>> - swap_entry_range_free(si, ci, swp_entry(si->type, offset), 1);
>> + swap_entries_free(si, ci, swp_entry(si->type, offset), 1);
>> } while (++offset < end);
>> unlock_cluster(ci);
>> }
>> @@ -1596,11 +1595,11 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
>>
>> ci = lock_cluster(si, offset);
>> if (swap_only_has_cache(si, offset, size))
>> - swap_entry_range_free(si, ci, entry, size);
>> + swap_entries_free(si, ci, entry, size);
>> else {
>> for (int i = 0; i < size; i++, entry.val++) {
>> if (!swap_entry_put_locked(si, offset + i, SWAP_HAS_CACHE))
>> - swap_entry_range_free(si, ci, entry, 1);
>> + swap_entries_free(si, ci, entry, 1);
>> }
>> }
>> unlock_cluster(ci);
>> --
>> 2.30.0
>>
>
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