Re: [PATCH 07/20] mm: zswap: break out zwap_compress()

[Chengming Zhou <zhouchengming@bytedance.com>]

On 2024/1/30 09:36, Johannes Weiner wrote:
> zswap_store() is long and mixes work at the zswap layer with work at
> the backend and compression layer. Move compression & backend work to
> zswap_compress(), mirroring zswap_decompress().
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Chengming Zhou <zhouchengming@bytedance.com>

> ---
>  mm/zswap.c | 145 ++++++++++++++++++++++++++++-------------------------
>  1 file changed, 77 insertions(+), 68 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index bdc9f82fe4b9..f9b9494156ba 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1316,6 +1316,79 @@ static int zswap_enabled_param_set(const char *val,
>  	return ret;
>  }
>  
> +static bool zswap_compress(struct folio *folio, struct zswap_entry *entry)
> +{
> +	struct crypto_acomp_ctx *acomp_ctx;
> +	struct scatterlist input, output;
> +	unsigned int dlen = PAGE_SIZE;
> +	unsigned long handle;
> +	struct zpool *zpool;
> +	char *buf;
> +	gfp_t gfp;
> +	int ret;
> +	u8 *dst;
> +
> +	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> +
> +	mutex_lock(&acomp_ctx->mutex);
> +
> +	dst = acomp_ctx->buffer;
> +	sg_init_table(&input, 1);
> +	sg_set_page(&input, &folio->page, PAGE_SIZE, 0);
> +
> +	/*
> +	 * We need PAGE_SIZE * 2 here since there maybe over-compression case,
> +	 * and hardware-accelerators may won't check the dst buffer size, so
> +	 * giving the dst buffer with enough length to avoid buffer overflow.
> +	 */
> +	sg_init_one(&output, dst, PAGE_SIZE * 2);
> +	acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
> +
> +	/*
> +	 * it maybe looks a little bit silly that we send an asynchronous request,
> +	 * then wait for its completion synchronously. This makes the process look
> +	 * synchronous in fact.
> +	 * Theoretically, acomp supports users send multiple acomp requests in one
> +	 * acomp instance, then get those requests done simultaneously. but in this
> +	 * case, zswap actually does store and load page by page, there is no
> +	 * existing method to send the second page before the first page is done
> +	 * in one thread doing zwap.
> +	 * but in different threads running on different cpu, we have different
> +	 * acomp instance, so multiple threads can do (de)compression in parallel.
> +	 */
> +	ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
> +	dlen = acomp_ctx->req->dlen;
> +	if (ret) {
> +		zswap_reject_compress_fail++;
> +		goto unlock;
> +	}
> +
> +	zpool = zswap_find_zpool(entry);
> +	gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> +	if (zpool_malloc_support_movable(zpool))
> +		gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> +	ret = zpool_malloc(zpool, dlen, gfp, &handle);
> +	if (ret == -ENOSPC) {
> +		zswap_reject_compress_poor++;
> +		goto unlock;
> +	}
> +	if (ret) {
> +		zswap_reject_alloc_fail++;
> +		goto unlock;
> +	}
> +
> +	buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
> +	memcpy(buf, dst, dlen);
> +	zpool_unmap_handle(zpool, handle);
> +
> +	entry->handle = handle;
> +	entry->length = dlen;
> +
> +unlock:
> +	mutex_unlock(&acomp_ctx->mutex);
> +	return ret == 0;
> +}
> +
>  static void zswap_decompress(struct zswap_entry *entry, struct page *page)
>  {
>  	struct zpool *zpool = zswap_find_zpool(entry);
> @@ -1472,18 +1545,11 @@ bool zswap_store(struct folio *folio)
>  	struct page *page = &folio->page;
>  	struct zswap_tree *tree = swap_zswap_tree(swp);
>  	struct zswap_entry *entry, *dupentry;
> -	struct scatterlist input, output;
> -	struct crypto_acomp_ctx *acomp_ctx;
>  	struct obj_cgroup *objcg = NULL;
>  	struct mem_cgroup *memcg = NULL;
>  	struct zswap_pool *pool;
> -	struct zpool *zpool;
> -	unsigned int dlen = PAGE_SIZE;
> -	unsigned long handle, value;
> -	char *buf;
> -	u8 *src, *dst;
> -	gfp_t gfp;
> -	int ret;
> +	unsigned long value;
> +	u8 *src;
>  
>  	VM_WARN_ON_ONCE(!folio_test_locked(folio));
>  	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
> @@ -1568,65 +1634,10 @@ bool zswap_store(struct folio *folio)
>  		mem_cgroup_put(memcg);
>  	}
>  
> -	/* compress */
> -	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> -
> -	mutex_lock(&acomp_ctx->mutex);
> -
> -	dst = acomp_ctx->buffer;
> -	sg_init_table(&input, 1);
> -	sg_set_page(&input, &folio->page, PAGE_SIZE, 0);
> +	if (!zswap_compress(folio, entry))
> +		goto put_pool;
>  
> -	/*
> -	 * We need PAGE_SIZE * 2 here since there maybe over-compression case,
> -	 * and hardware-accelerators may won't check the dst buffer size, so
> -	 * giving the dst buffer with enough length to avoid buffer overflow.
> -	 */
> -	sg_init_one(&output, dst, PAGE_SIZE * 2);
> -	acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
> -	/*
> -	 * it maybe looks a little bit silly that we send an asynchronous request,
> -	 * then wait for its completion synchronously. This makes the process look
> -	 * synchronous in fact.
> -	 * Theoretically, acomp supports users send multiple acomp requests in one
> -	 * acomp instance, then get those requests done simultaneously. but in this
> -	 * case, zswap actually does store and load page by page, there is no
> -	 * existing method to send the second page before the first page is done
> -	 * in one thread doing zwap.
> -	 * but in different threads running on different cpu, we have different
> -	 * acomp instance, so multiple threads can do (de)compression in parallel.
> -	 */
> -	ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
> -	dlen = acomp_ctx->req->dlen;
> -
> -	if (ret) {
> -		zswap_reject_compress_fail++;
> -		goto put_dstmem;
> -	}
> -
> -	/* store */
> -	zpool = zswap_find_zpool(entry);
> -	gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> -	if (zpool_malloc_support_movable(zpool))
> -		gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> -	ret = zpool_malloc(zpool, dlen, gfp, &handle);
> -	if (ret == -ENOSPC) {
> -		zswap_reject_compress_poor++;
> -		goto put_dstmem;
> -	}
> -	if (ret) {
> -		zswap_reject_alloc_fail++;
> -		goto put_dstmem;
> -	}
> -	buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
> -	memcpy(buf, dst, dlen);
> -	zpool_unmap_handle(zpool, handle);
> -	mutex_unlock(&acomp_ctx->mutex);
> -
> -	/* populate entry */
>  	entry->swpentry = swp;
> -	entry->handle = handle;
> -	entry->length = dlen;
>  
>  insert_entry:
>  	entry->objcg = objcg;
> @@ -1663,8 +1674,6 @@ bool zswap_store(struct folio *folio)
>  
>  	return true;
>  
> -put_dstmem:
> -	mutex_unlock(&acomp_ctx->mutex);
>  put_pool:
>  	zswap_pool_put(entry->pool);
>  freepage: