Date:   Mon, 27 Feb 2017 20:10:08 +0530
From:   Mahipal Reddy <mahipalreddy2006@...il.com>
To:     Dan Streetman <ddstreet@...e.org>
Cc:     Mahipal Challa <Mahipal.Challa@...ium.com>,
        Seth Jennings <sjenning@...hat.com>,
        Linux-MM <linux-mm@...ck.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        linux-kernel <linux-kernel@...r.kernel.org>, pathreya@...ium.com,
        Vishnu Nair <Vishnu.Nair@...ium.com>
Subject: Re: [PATCH v2 1/1] mm: zswap - Add crypto acomp/scomp framework support

Hi Dan,
Thanks for your reply.

On Sat, Feb 25, 2017 at 3:51 AM, Dan Streetman <ddstreet@...e.org> wrote:
> On Fri, Feb 24, 2017 at 11:05 AM, Mahipal Challa
> <Mahipal.Challa@...ium.com> wrote:
>> This adds support for kernel's new crypto acomp/scomp framework
>> to zswap.
>
> I don't understand the point of this, zswap can't compress pages
> asynchronously, so what benefit do we get from using the async crypto
> api and then immediately waiting for it to finish?  This seems like
> it's just adding complexity for no reason?

1) The new crypto acomp/scomp framework, provides both synchronous and
asynchronous comp/decomp
functionality with the same async-crypto(acomp) api(include/crypto/acompress.h).

2) Currently with new crypto acomp/scomp framework, the crypto
sub-system(crypto/lzo.c, crypto/deflate.c)
only supports synchronous mode of compression/decompression which
meets the zswap requirement.

3) The new crypto acomp/scomp framework is introduced in the 4.10.xx kernel.
With this new framework, according to Herbert Xu, existing crypto
comp(CRYPTO_ALG_TYPE_COMPRESS ) api
is going to be deprecated (which zswap uses).

4) Applications like zswap, which use comp/decomp of crypto subsystem,
at some point will have to be ported to
the new framework.

Regards,
-Mahipal

>> Signed-off-by: Mahipal Challa <Mahipal.Challa@...ium.com>
>> Signed-off-by: Vishnu Nair <Vishnu.Nair@...ium.com>
>> ---
>>  mm/zswap.c | 192 +++++++++++++++++++++++++++++++++++++++++++++++++++----------
>>  1 file changed, 162 insertions(+), 30 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index cabf09e..b29d109 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -33,8 +33,10 @@
>>  #include <linux/rbtree.h>
>>  #include <linux/swap.h>
>>  #include <linux/crypto.h>
>> +#include <linux/scatterlist.h>
>>  #include <linux/mempool.h>
>>  #include <linux/zpool.h>
>> +#include <crypto/acompress.h>
>>
>>  #include <linux/mm_types.h>
>>  #include <linux/page-flags.h>
>> @@ -118,9 +120,21 @@ static int zswap_compressor_param_set(const char *,
>>  * data structures
>>  **********************************/
>>
>> +/**
>> + * struct zswap_acomp_result - Data structure to store result of acomp callback
>> + * @completion: zswap will wait for completion on this entry
>> + * @err       : return value from acomp algorithm will be stored here
>> + */
>> +struct zswap_acomp_result {
>> +       struct completion completion;
>> +       int err;
>> +};
>> +
>>  struct zswap_pool {
>>         struct zpool *zpool;
>> -       struct crypto_comp * __percpu *tfm;
>> +       struct crypto_acomp * __percpu *acomp;
>> +       struct acomp_req * __percpu *acomp_req;
>> +       struct zswap_acomp_result * __percpu *result;
>>         struct kref kref;
>>         struct list_head list;
>>         struct work_struct work;
>> @@ -388,30 +402,66 @@ static int zswap_dstmem_dead(unsigned int cpu)
>>  static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
>>  {
>>         struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
>> -       struct crypto_comp *tfm;
>> +       struct crypto_acomp *acomp;
>> +       struct acomp_req *acomp_req;
>> +       struct zswap_acomp_result *result;
>>
>> -       if (WARN_ON(*per_cpu_ptr(pool->tfm, cpu)))
>> +       if (WARN_ON(*per_cpu_ptr(pool->acomp, cpu)))
>>                 return 0;
>> +       if (WARN_ON(*per_cpu_ptr(pool->acomp_req, cpu)))
>> +               return 0;
>> +       if (WARN_ON(*per_cpu_ptr(pool->result, cpu)))
>> +               return 0;
>> +
>> +       acomp = crypto_alloc_acomp(pool->tfm_name, 0, 0);
>> +       if (IS_ERR_OR_NULL(acomp)) {
>> +               pr_err("could not alloc crypto acomp %s : %ld\n",
>> +                      pool->tfm_name, PTR_ERR(acomp));
>> +               return -ENOMEM;
>> +       }
>> +       *per_cpu_ptr(pool->acomp, cpu) = acomp;
>> +
>> +       acomp_req = acomp_request_alloc(acomp);
>> +       if (IS_ERR_OR_NULL(acomp_req)) {
>> +               pr_err("could not alloc crypto acomp %s : %ld\n",
>> +                      pool->tfm_name, PTR_ERR(acomp));
>> +               return -ENOMEM;
>> +       }
>> +       *per_cpu_ptr(pool->acomp_req, cpu) = acomp_req;
>>
>> -       tfm = crypto_alloc_comp(pool->tfm_name, 0, 0);
>> -       if (IS_ERR_OR_NULL(tfm)) {
>> -               pr_err("could not alloc crypto comp %s : %ld\n",
>> -                      pool->tfm_name, PTR_ERR(tfm));
>> +       result = kzalloc(sizeof(*result), GFP_KERNEL);
>> +       if (IS_ERR_OR_NULL(result)) {
>> +               pr_err("Could not initialize completion on result\n");
>>                 return -ENOMEM;
>>         }
>> -       *per_cpu_ptr(pool->tfm, cpu) = tfm;
>> +       init_completion(&result->completion);
>> +       *per_cpu_ptr(pool->result, cpu) = result;
>> +
>>         return 0;
>>  }
>>
>>  static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node)
>>  {
>>         struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
>> -       struct crypto_comp *tfm;
>> +       struct crypto_acomp *acomp;
>> +       struct acomp_req *acomp_req;
>> +       struct zswap_acomp_result *result;
>> +
>> +       acomp_req = *per_cpu_ptr(pool->acomp_req, cpu);
>> +       if (!IS_ERR_OR_NULL(acomp_req))
>> +               acomp_request_free(acomp_req);
>> +       *per_cpu_ptr(pool->acomp_req, cpu) = NULL;
>> +
>> +       acomp = *per_cpu_ptr(pool->acomp, cpu);
>> +       if (!IS_ERR_OR_NULL(acomp))
>> +               crypto_free_acomp(acomp);
>> +       *per_cpu_ptr(pool->acomp, cpu) = NULL;
>> +
>> +       result = *per_cpu_ptr(pool->result, cpu);
>> +       if (!IS_ERR_OR_NULL(result))
>> +               kfree(result);
>> +       *per_cpu_ptr(pool->result, cpu) = NULL;
>>
>> -       tfm = *per_cpu_ptr(pool->tfm, cpu);
>> -       if (!IS_ERR_OR_NULL(tfm))
>> -               crypto_free_comp(tfm);
>> -       *per_cpu_ptr(pool->tfm, cpu) = NULL;
>>         return 0;
>>  }
>>
>> @@ -512,8 +562,20 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
>>         pr_debug("using %s zpool\n", zpool_get_type(pool->zpool));
>>
>>         strlcpy(pool->tfm_name, compressor, sizeof(pool->tfm_name));
>> -       pool->tfm = alloc_percpu(struct crypto_comp *);
>> -       if (!pool->tfm) {
>> +       pool->acomp = alloc_percpu(struct crypto_acomp *);
>> +       if (!pool->acomp) {
>> +               pr_err("percpu alloc failed\n");
>> +               goto error;
>> +       }
>> +
>> +       pool->acomp_req = alloc_percpu(struct acomp_req *);
>> +       if (!pool->acomp_req) {
>> +               pr_err("percpu alloc failed\n");
>> +               goto error;
>> +       }
>> +
>> +       pool->result = alloc_percpu(struct zswap_acomp_result *);
>> +       if (!pool->result) {
>>                 pr_err("percpu alloc failed\n");
>>                 goto error;
>>         }
>> @@ -535,7 +597,9 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
>>         return pool;
>>
>>  error:
>> -       free_percpu(pool->tfm);
>> +       free_percpu(pool->result);
>> +       free_percpu(pool->acomp_req);
>> +       free_percpu(pool->acomp);
>>         if (pool->zpool)
>>                 zpool_destroy_pool(pool->zpool);
>>         kfree(pool);
>> @@ -575,7 +639,9 @@ static void zswap_pool_destroy(struct zswap_pool *pool)
>>         zswap_pool_debug("destroying", pool);
>>
>>         cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
>> -       free_percpu(pool->tfm);
>> +       free_percpu(pool->result);
>> +       free_percpu(pool->acomp_req);
>> +       free_percpu(pool->acomp);
>>         zpool_destroy_pool(pool->zpool);
>>         kfree(pool);
>>  }
>> @@ -622,6 +688,30 @@ static void zswap_pool_put(struct zswap_pool *pool)
>>  }
>>
>>  /*********************************
>> +* CRYPTO_ACOMPRESS wait and callbacks
>> +**********************************/
>> +static void zswap_acomp_callback(struct crypto_async_request *req, int err)
>> +{
>> +       struct zswap_acomp_result *res = req->data;
>> +
>> +       if (err == -EINPROGRESS)
>> +               return;
>> +
>> +       res->err = err;
>> +       complete(&res->completion);
>> +}
>> +
>> +static int zswap_wait_acomp(struct zswap_acomp_result *res, int ret)
>> +{
>> +       if (ret == -EINPROGRESS || ret == -EBUSY) {
>> +               wait_for_completion(&res->completion);
>> +               reinit_completion(&res->completion);
>> +               ret = res->err;
>> +       }
>> +       return ret;
>> +}
>> +
>> +/*********************************
>>  * param callbacks
>>  **********************************/
>>
>> @@ -788,7 +878,9 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
>>         pgoff_t offset;
>>         struct zswap_entry *entry;
>>         struct page *page;
>> -       struct crypto_comp *tfm;
>> +       struct scatterlist input, output;
>> +       struct acomp_req *req;
>> +       struct zswap_acomp_result *result;
>>         u8 *src, *dst;
>>         unsigned int dlen;
>>         int ret;
>> @@ -828,14 +920,25 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
>>
>>         case ZSWAP_SWAPCACHE_NEW: /* page is locked */
>>                 /* decompress */
>> +               req = *get_cpu_ptr(entry->pool->acomp_req);
>>                 dlen = PAGE_SIZE;
>>                 src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle,
>>                                 ZPOOL_MM_RO) + sizeof(struct zswap_header);
>>                 dst = kmap_atomic(page);
>> -               tfm = *get_cpu_ptr(entry->pool->tfm);
>> -               ret = crypto_comp_decompress(tfm, src, entry->length,
>> -                                            dst, &dlen);
>> -               put_cpu_ptr(entry->pool->tfm);
>> +
>> +               result = *get_cpu_ptr(entry->pool->result);
>> +               sg_init_one(&input, src, entry->length);
>> +               sg_init_one(&output, dst, dlen);
>> +               acomp_request_set_params(req, &input, &output, entry->length,
>> +                                        dlen);
>> +               acomp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
>> +                                          zswap_acomp_callback, result);
>> +
>> +               ret = zswap_wait_acomp(result, crypto_acomp_decompress(req));
>> +
>> +               dlen = req->dlen;
>> +               put_cpu_ptr(entry->pool->acomp_req);
>> +               put_cpu_ptr(entry->pool->result);
>>                 kunmap_atomic(dst);
>>                 zpool_unmap_handle(entry->pool->zpool, entry->handle);
>>                 BUG_ON(ret);
>> @@ -911,7 +1014,9 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>>  {
>>         struct zswap_tree *tree = zswap_trees[type];
>>         struct zswap_entry *entry, *dupentry;
>> -       struct crypto_comp *tfm;
>> +       struct scatterlist input, output;
>> +       struct acomp_req *req;
>> +       struct zswap_acomp_result *result;
>>         int ret;
>>         unsigned int dlen = PAGE_SIZE, len;
>>         unsigned long handle;
>> @@ -950,12 +1055,24 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>>         }
>>
>>         /* compress */
>> +       req = *get_cpu_ptr(entry->pool->acomp_req);
>> +       result = *get_cpu_ptr(entry->pool->result);
>> +
>>         dst = get_cpu_var(zswap_dstmem);
>> -       tfm = *get_cpu_ptr(entry->pool->tfm);
>>         src = kmap_atomic(page);
>> -       ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen);
>> +
>> +       sg_init_one(&input, src, PAGE_SIZE);
>> +       /* zswap_dstmem is of size (PAGE_SIZE * 2). Reflect same in sg_list */
>> +       sg_init_one(&output, dst, PAGE_SIZE * 2);
>> +       acomp_request_set_params(req, &input, &output, PAGE_SIZE, dlen);
>> +       acomp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
>> +                                  zswap_acomp_callback, result);
>> +
>> +       ret = zswap_wait_acomp(result, crypto_acomp_compress(req));
>>         kunmap_atomic(src);
>> -       put_cpu_ptr(entry->pool->tfm);
>> +       put_cpu_ptr(entry->pool->acomp_req);
>> +       put_cpu_ptr(entry->pool->result);
>> +       dlen = req->dlen;
>>         if (ret) {
>>                 ret = -EINVAL;
>>                 goto put_dstmem;
>> @@ -1023,7 +1140,9 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>>  {
>>         struct zswap_tree *tree = zswap_trees[type];
>>         struct zswap_entry *entry;
>> -       struct crypto_comp *tfm;
>> +       struct scatterlist input, output;
>> +       struct acomp_req *req;
>> +       struct zswap_acomp_result *result;
>>         u8 *src, *dst;
>>         unsigned int dlen;
>>         int ret;
>> @@ -1039,13 +1158,25 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>>         spin_unlock(&tree->lock);
>>
>>         /* decompress */
>> +       req = *get_cpu_ptr(entry->pool->acomp_req);
>> +       result = *get_cpu_ptr(entry->pool->result);
>> +
>>         dlen = PAGE_SIZE;
>>         src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle,
>>                         ZPOOL_MM_RO) + sizeof(struct zswap_header);
>>         dst = kmap_atomic(page);
>> -       tfm = *get_cpu_ptr(entry->pool->tfm);
>> -       ret = crypto_comp_decompress(tfm, src, entry->length, dst, &dlen);
>> -       put_cpu_ptr(entry->pool->tfm);
>> +
>> +       sg_init_one(&input, src, entry->length);
>> +       sg_init_one(&output, dst, dlen);
>> +       acomp_request_set_params(req, &input, &output, entry->length, dlen);
>> +       acomp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
>> +                                  zswap_acomp_callback, result);
>> +
>> +       ret = zswap_wait_acomp(result, crypto_acomp_decompress(req));
>> +
>> +       dlen = req->dlen;
>> +       put_cpu_ptr(entry->pool->acomp_req);
>> +       put_cpu_ptr(entry->pool->result);
>>         kunmap_atomic(dst);
>>         zpool_unmap_handle(entry->pool->zpool, entry->handle);
>>         BUG_ON(ret);
>> @@ -1237,3 +1368,4 @@ static int __init init_zswap(void)
>>  MODULE_LICENSE("GPL");
>>  MODULE_AUTHOR("Seth Jennings <sjennings@...iantweb.net>");
>>  MODULE_DESCRIPTION("Compressed cache for swap pages");
>> +
>> --
>> 1.8.3.1
>>
>
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