On 12/04/2024 03:07, Chuanhua Han wrote:
> Ryan Roberts <ryan.roberts@xxxxxxx> 于2024年4月11日周四 22:30写道：
>>
>> On 09/04/2024 09:26, Barry Song wrote:
>>> From: Chuanhua Han <hanchuanhua@xxxxxxxx>
>>>
>>> While swapping in a large folio, we need to free swaps related to the whole
>>> folio. To avoid frequently acquiring and releasing swap locks, it is better
>>> to introduce an API for batched free.
>>>
>>> Signed-off-by: Chuanhua Han <hanchuanhua@xxxxxxxx>
>>> Co-developed-by: Barry Song <v-songbaohua@xxxxxxxx>
>>> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
>>
>> Couple of nits; feel free to ignore.
>>
>> Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx>
>>
>>> ---
>>> include/linux/swap.h | 5 +++++
>>> mm/swapfile.c | 51 ++++++++++++++++++++++++++++++++++++++++++++
>>> 2 files changed, 56 insertions(+)
>>>
>>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>>> index 11c53692f65f..b7a107e983b8 100644
>>> --- a/include/linux/swap.h
>>> +++ b/include/linux/swap.h
>>> @@ -483,6 +483,7 @@ extern void swap_shmem_alloc(swp_entry_t);
>>> extern int swap_duplicate(swp_entry_t);
>>> extern int swapcache_prepare(swp_entry_t);
>>> extern void swap_free(swp_entry_t);
>>> +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);
>>> int swap_type_of(dev_t device, sector_t offset);
>>> @@ -564,6 +565,10 @@ static inline void swap_free(swp_entry_t swp)
>>> {
>>> }
>>>
>>> +void swap_free_nr(swp_entry_t entry, int nr_pages)
>>> +{
>>> +}
>>> +
>>> static inline void put_swap_folio(struct folio *folio, swp_entry_t swp)
>>> {
>>> }
>>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>>> index 28642c188c93..f4c65aeb088d 100644
>>> --- a/mm/swapfile.c
>>> +++ b/mm/swapfile.c
>>> @@ -1356,6 +1356,57 @@ void swap_free(swp_entry_t entry)
>>> __swap_entry_free(p, entry);
>>> }
>>>
>>> +/*
>>> + * Free up the maximum number of swap entries at once to limit the
>>> + * maximum kernel stack usage.
>>> + */
>>> +#define SWAP_BATCH_NR (SWAPFILE_CLUSTER > 512 ? 512 : SWAPFILE_CLUSTER)
>>> +
>>> +/*
>>> + * Called after swapping in a large folio, batched free swap entries
>>> + * for this large folio, entry should be for the first subpage and
>>> + * its offset is aligned with nr_pages
>>> + */
>>> +void swap_free_nr(swp_entry_t entry, int nr_pages)
>>> +{
>>> + int i, j;
>>> + struct swap_cluster_info *ci;
>>> + struct swap_info_struct *p;
>>> + unsigned int type = swp_type(entry);
>>> + unsigned long offset = swp_offset(entry);
>>> + int batch_nr, remain_nr;
>>> + DECLARE_BITMAP(usage, SWAP_BATCH_NR) = { 0 };
>>> +
>>> + /* all swap entries are within a cluster for mTHP */
>>> + VM_BUG_ON(offset % SWAPFILE_CLUSTER + nr_pages > SWAPFILE_CLUSTER);
>>> +
>>> + if (nr_pages == 1) {
>>> + swap_free(entry);
>>> + return;
>>> + }
>>> +
>>> + remain_nr = nr_pages;
>>> + p = _swap_info_get(entry);
>>> + if (p) {
>>
>> nit: perhaps return early if (!p) ? Then you dedent the for() block.
>
> Agreed!
>
>>
>>> + for (i = 0; i < nr_pages; i += batch_nr) {
>>> + batch_nr = min_t(int, SWAP_BATCH_NR, remain_nr);
>>> +
>>> + ci = lock_cluster_or_swap_info(p, offset);
>>> + for (j = 0; j < batch_nr; j++) {
>>> + if (__swap_entry_free_locked(p, offset + i * SWAP_BATCH_NR + j, 1))
>>> + __bitmap_set(usage, j, 1);
>>> + }
>>> + unlock_cluster_or_swap_info(p, ci);
>>> +
>>> + for_each_clear_bit(j, usage, batch_nr)
>>> + free_swap_slot(swp_entry(type, offset + i * SWAP_BATCH_NR + j));
>>> +
>>
>> nit: perhaps change to for (;;), and do the checks here to avoid clearing the
>> bitmap on the last run:
>>
>> i += batch_nr;
>> if (i < nr_pages)
>> break;
> Great, thank you for your advice!
Or maybe leave the for() as is, but don't explicitly init the bitmap at the
start of the function and instead call:
bitmap_clear(usage, 0, SWAP_BATCH_NR);
At the start of each loop?
>>
>>> + bitmap_clear(usage, 0, SWAP_BATCH_NR);
>>> + remain_nr -= batch_nr;
>>> + }
>>> + }
>>> +}
>>> +
>>> /*
>>> * Called after dropping swapcache to decrease refcnt to swap entries.
>>> */
>>
>>
>
>
