Re: [PATCH 5/7] mm/zswap: refactor out __zswap_load()

[Chengming Zhou <zhouchengming@bytedance.com>]

On 2023/12/13 07:13, Nhat Pham wrote:
> On Wed, Dec 6, 2023 at 1:46 AM Chengming Zhou
> <zhouchengming@bytedance.com> wrote:
>>
>> The zswap_load() and zswap_writeback_entry() have the same part that
>> decompress the data from zswap_entry to page, so refactor out the
>> common part as __zswap_load(entry, page).
> 
> I love this refactoring a lot :) No reason why we should duplicate the
> decompression logic shared between load and writeback.
> 
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
>> ---
>>  mm/zswap.c | 108 ++++++++++++++++++++++---------------------------------------
>>  1 file changed, 39 insertions(+), 69 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 999671dcb469..667b66a3911b 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -1380,6 +1380,42 @@ static int zswap_enabled_param_set(const char *val,
>>         return ret;
>>  }
>>
>> +static void __zswap_load(struct zswap_entry *entry, struct page *page)
>> +{
>> +       struct scatterlist input, output;
>> +       unsigned int dlen = PAGE_SIZE;
>> +       struct crypto_acomp_ctx *acomp_ctx;
>> +       struct zpool *zpool;
>> +       u8 *src;
>> +       int ret;
>> +
>> +       /* decompress */
> 
> nit: I guess all this function does is decompression right? Doesn't
> seem like this comment is necessary anymore... But this is just
> nitpicking.
> 

Ah, right. I will remove it.

Thanks!

>> +       acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>> +       mutex_lock(acomp_ctx->mutex);
>> +
>> +       zpool = zswap_find_zpool(entry);
>> +       src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
>> +       if (!zpool_can_sleep_mapped(zpool)) {
>> +               memcpy(acomp_ctx->dstmem, src, entry->length);
>> +               src = acomp_ctx->dstmem;
>> +               zpool_unmap_handle(zpool, entry->handle);
>> +       }
>> +
>> +       sg_init_one(&input, src, entry->length);
>> +       sg_init_table(&output, 1);
>> +       sg_set_page(&output, page, PAGE_SIZE, 0);
>> +       acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
>> +       ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
>> +       dlen = acomp_ctx->req->dlen;
>> +       mutex_unlock(acomp_ctx->mutex);
>> +
>> +       if (zpool_can_sleep_mapped(zpool))
>> +               zpool_unmap_handle(zpool, entry->handle);
>> +
>> +       BUG_ON(ret);
>> +       BUG_ON(dlen != PAGE_SIZE);
>> +}
>> +
>>  /*********************************
>>  * writeback code
>>  **********************************/
>> @@ -1401,23 +1437,12 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>>         swp_entry_t swpentry = entry->swpentry;
>>         struct page *page;
>>         struct mempolicy *mpol;
>> -       struct scatterlist input, output;
>> -       struct crypto_acomp_ctx *acomp_ctx;
>> -       struct zpool *pool = zswap_find_zpool(entry);
>>         bool page_was_allocated;
>> -       u8 *src, *tmp = NULL;
>> -       unsigned int dlen;
>>         int ret;
>>         struct writeback_control wbc = {
>>                 .sync_mode = WB_SYNC_NONE,
>>         };
>>
>> -       if (!zpool_can_sleep_mapped(pool)) {
>> -               tmp = kmalloc(PAGE_SIZE, GFP_KERNEL);
>> -               if (!tmp)
>> -                       return -ENOMEM;
>> -       }
>> -
> 
> Sweet. Less allocation == more efficient + less failure case :)
> 
>>         /* try to allocate swap cache page */
>>         mpol = get_task_policy(current);
>>         page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
>> @@ -1450,33 +1475,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>>         }
>>         spin_unlock(&tree->lock);
>>
>> -       /* decompress */
>> -       acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>> -       dlen = PAGE_SIZE;
>> -
>> -       src = zpool_map_handle(pool, entry->handle, ZPOOL_MM_RO);
>> -       if (!zpool_can_sleep_mapped(pool)) {
>> -               memcpy(tmp, src, entry->length);
>> -               src = tmp;
>> -               zpool_unmap_handle(pool, entry->handle);
>> -       }
>> -
>> -       mutex_lock(acomp_ctx->mutex);
>> -       sg_init_one(&input, src, entry->length);
>> -       sg_init_table(&output, 1);
>> -       sg_set_page(&output, page, PAGE_SIZE, 0);
>> -       acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
>> -       ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
>> -       dlen = acomp_ctx->req->dlen;
>> -       mutex_unlock(acomp_ctx->mutex);
>> -
>> -       if (!zpool_can_sleep_mapped(pool))
>> -               kfree(tmp);
>> -       else
>> -               zpool_unmap_handle(pool, entry->handle);
>> -
>> -       BUG_ON(ret);
>> -       BUG_ON(dlen != PAGE_SIZE);
>> +       __zswap_load(entry, page);
>>
>>         /* page is up to date */
>>         SetPageUptodate(page);
>> @@ -1496,9 +1495,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>>         return ret;
>>
>>  fail:
>> -       if (!zpool_can_sleep_mapped(pool))
>> -               kfree(tmp);
>> -
>>         /*
>>          * If we get here because the page is already in swapcache, a
>>          * load may be happening concurrently. It is safe and okay to
>> @@ -1755,11 +1751,7 @@ bool zswap_load(struct folio *folio)
>>         struct page *page = &folio->page;
>>         struct zswap_tree *tree = swap_zswap_tree(swp);
>>         struct zswap_entry *entry;
>> -       struct scatterlist input, output;
>> -       struct crypto_acomp_ctx *acomp_ctx;
>> -       unsigned int dlen = PAGE_SIZE;
>> -       u8 *src, *dst;
>> -       struct zpool *zpool;
>> +       u8 *dst;
>>         bool ret;
>>
>>         VM_WARN_ON_ONCE(!folio_test_locked(folio));
>> @@ -1781,29 +1773,7 @@ bool zswap_load(struct folio *folio)
>>                 goto stats;
>>         }
>>
>> -       /* decompress */
>> -       acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>> -       mutex_lock(acomp_ctx->mutex);
>> -
>> -       zpool = zswap_find_zpool(entry);
>> -       src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
>> -       if (!zpool_can_sleep_mapped(zpool)) {
>> -               memcpy(acomp_ctx->dstmem, src, entry->length);
>> -               src = acomp_ctx->dstmem;
>> -               zpool_unmap_handle(zpool, entry->handle);
>> -       }
>> -
>> -       sg_init_one(&input, src, entry->length);
>> -       sg_init_table(&output, 1);
>> -       sg_set_page(&output, page, PAGE_SIZE, 0);
>> -       acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
>> -       if (crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait))
>> -               WARN_ON(1);
>> -       mutex_unlock(acomp_ctx->mutex);
>> -
>> -       if (zpool_can_sleep_mapped(zpool))
>> -               zpool_unmap_handle(zpool, entry->handle);
>> -
>> +       __zswap_load(entry, page);
>>         ret = true;
>>  stats:
>>         count_vm_event(ZSWPIN);
>>
>> --
>> b4 0.10.1
> 
> Can't find anything wrong with this patch, so:
> Reviewed-by: Nhat Pham <nphamcs@gmail.com>