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

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>