linux-kernel - [PATCH] mm: zsmalloc: return -ENOSPC rather than -EINVAL in zs

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Date: Thu, 28 Dec 2023 19:18:02 +1300
From: Barry Song <21cnbao@...il.com>
To: minchan@...nel.org,
	senozhatsky@...omium.org,
	akpm@...ux-foundation.org,
	linux-mm@...ck.org,
	ddstreet@...e.org,
	sjenning@...hat.com,
	vitaly.wool@...sulko.com
Cc: linux-kernel@...r.kernel.org,
	chriscli@...gle.com,
	chrisl@...nel.org,
	hannes@...xchg.org,
	yosryahmed@...gle.com,
	zhouchengming@...edance.com,
	nphamcs@...il.com,
	Barry Song <v-songbaohua@...o.com>
Subject: [PATCH] mm: zsmalloc: return -ENOSPC rather than -EINVAL in zs_malloc while size is too large

This is the case the "compressed" data is larger than the original data,
it is better to return -ENOSPC which can help zswap record a poor compr
rather than an invalid request. Then we get more friendly counting for
reject_compress_poor in debugfs.

 bool zswap_store(struct folio *folio)
 {
 	...
 	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;
 	}
 	...
 }

Also, zbud_alloc() and z3fold_alloc() are returning ENOSPC in the same
case, eg
 static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
 			unsigned long *handle)
 {
 	...
 	if (!size || (gfp & __GFP_HIGHMEM))
 		return -EINVAL;

 	if (size > PAGE_SIZE)
 		return -ENOSPC;
 	...
 }

Signed-off-by: Barry Song <v-songbaohua@...o.com>
---
 mm/zsmalloc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index b1c0dad7f4cf..c937635e0ad1 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1364,9 +1364,12 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
 	int newfg;
 	struct zspage *zspage;
 
-	if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
+	if (unlikely(!size))
 		return (unsigned long)ERR_PTR(-EINVAL);
 
+	if (unlikely(size > ZS_MAX_ALLOC_SIZE))
+		return (unsigned long)ERR_PTR(-ENOSPC);
+
 	handle = cache_alloc_handle(pool, gfp);
 	if (!handle)
 		return (unsigned long)ERR_PTR(-ENOMEM);
-- 
2.34.1