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

[Barry Song]

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>
---
 -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);
-- 
2.34.1