mm/zswap: reduce the size of the compression buffer to a single page

Reduce the compression buffer size from 2 * PAGE_SIZE to only one page, as
the compression output (in the success case) should not exceed the length
of the input.

In the past, Chengming tried to reduce the compression buffer size, but
ran into issues with the LZO algorithm (see [2]).  Herbert Xu reported
that the issue has been fixed (see [3]).  Now we should have the guarantee
that compressors' output should not exceed one page in the success case,
and the algorithm will just report failure otherwise.

With this patch, we save one page per cpu (per compression algorithm).

Link: https://lkml.kernel.org/r/20250820181547.3794167-1-nphamcs@gmail.com
Link: https://lore.kernel.org/linux-mm/20231213-zswap-dstmem-v4-1-f228b059dd89@bytedance.com/
Link: https://lore.kernel.org/lkml/0000000000000b05cd060d6b5511@google.com/
Link: https://lore.kernel.org/linux-mm/aKUmyl5gUFCdXGn-@gondor.apana.org.au/
Co-developed-by: Chengming Zhou <chengming.zhou@linux.dev>
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zswap.c b/mm/zswap.c
index 0c8dd8876d8eec17da47a65afd66def744a2d9de..e5e1f5687f5ef3462ecc4a2016990163791de453 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -831,7 +831,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
        u8 *buffer = NULL;
        int ret;
 
-       buffer = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
+       buffer = kmalloc_node(PAGE_SIZE, GFP_KERNEL, cpu_to_node(cpu));
        if (!buffer) {
                ret = -ENOMEM;
                goto fail;
@@ -959,12 +959,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
        sg_init_table(&input, 1);
        sg_set_page(&input, 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);
+       sg_init_one(&output, dst, PAGE_SIZE);
        acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
 
        /*