erofs: avoid refcounting short-lived pages

erofs: avoid refcounting short-lived pages

LZ4 always reuses the decompressed buffer as its LZ77 sliding window
(dynamic dictionary) for optimal performance.  However, in specific
cases, the output buffer may not fully contain valid page cache pages,
resulting in the use of short-lived pages for temporary purposes.

Due to the limited sliding window size, LZ4 shortlived bounce pages can
also be reused in a sliding manner, so each bounce page can be vmapped
multiple times in different relative positions by design.  In order to
avoiding double frees, currently, reuse counts are recorded via page
refcount, but it will no longer be used as-is in the future world of
Memdescs.

Just maintain a lookup table to check if a shortlived page is reused.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240711053659.1364989-1-hsiangkao@linux.alibaba.com