Re: [PATCH v2] mm: zswap: increase reject_compress_poor but not reject_compress_fail if compression returns ENOSPC

[Chengming Zhou]

On 2024/2/17 13:36, Barry Song wrote:
> From: Barry Song <v-songbaohua@xxxxxxxx>
> 
> We used to rely on the returned -ENOSPC of zpool_malloc() to increase
> reject_compress_poor. But the code wouldn't get to there after commit
> 744e1885922a ("crypto: scomp - fix req->dst buffer overflow") as the
> new code will goto out immediately after the special compression case
> happens. So there might be no longer a chance to execute zpool_malloc
> now. We are incorrectly increasing zswap_reject_compress_fail instead.
> Thus, we need to fix the counters handling right after compressions
> return ENOSPC. This patch also centralizes the counters handling for
> all of compress_poor, compress_fail and alloc_fail.
> 
> Fixes: 744e1885922a ("crypto: scomp - fix req->dst buffer overflow")
> Cc: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> Cc: Nhat Pham <nphamcs@xxxxxxxxx>
> Cc: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>

LGTM, thanks!

Reviewed-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>

> ---
>  -v2: 
>  * correct the fixes target according to Yosry, Chengming, Nhat's
>    comments;
>  * centralize the counters handling according to Yosry's comment
> 
>  mm/zswap.c | 25 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 350dd2fc8159..47cf07d56362 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1498,6 +1498,7 @@ bool zswap_store(struct folio *folio)
>  	struct zswap_tree *tree = zswap_trees[type];
>  	struct zswap_entry *entry, *dupentry;
>  	struct scatterlist input, output;
> +	int comp_ret = 0, alloc_ret = 0;
>  	struct crypto_acomp_ctx *acomp_ctx;
>  	struct obj_cgroup *objcg = NULL;
>  	struct mem_cgroup *memcg = NULL;
> @@ -1508,7 +1509,6 @@ bool zswap_store(struct folio *folio)
>  	char *buf;
>  	u8 *src, *dst;
>  	gfp_t gfp;
> -	int ret;
>  
>  	VM_WARN_ON_ONCE(!folio_test_locked(folio));
>  	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
> @@ -1621,28 +1621,20 @@ bool zswap_store(struct folio *folio)
>  	 * 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);
> +	comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
>  	dlen = acomp_ctx->req->dlen;
>  
> -	if (ret) {
> -		zswap_reject_compress_fail++;
> +	if (comp_ret)
>  		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++;
> +	alloc_ret = zpool_malloc(zpool, dlen, gfp, &handle);
> +	if (alloc_ret)
>  		goto put_dstmem;
> -	}
>  	buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
>  	memcpy(buf, dst, dlen);
>  	zpool_unmap_handle(zpool, handle);
> @@ -1689,6 +1681,13 @@ bool zswap_store(struct folio *folio)
>  	return true;
>  
>  put_dstmem:
> +	if (comp_ret == -ENOSPC || alloc_ret == -ENOSPC)
> +		zswap_reject_compress_poor++;
> +	else if (comp_ret)
> +		zswap_reject_compress_fail++;
> +	else if (alloc_ret)
> +		zswap_reject_alloc_fail++;
> +
>  	mutex_unlock(&acomp_ctx->mutex);
>  put_pool:
>  	zswap_pool_put(entry->pool);