selftests: mincore: count file-mmap readahead on both sides

check_file_mmap() faults a page in the middle of a file mapping and
expects the mmap read-around path to make neighbouring pages resident. 
The test currently counts only pages after the faulted page.

That misses valid read-around on systems with large base page sizes.  On
arm64 with 64K pages and the default 128K readahead setting, the
read-around window is two pages wide and centred on the faulting page. 
Faulting page 32 makes pages 31 and 32 resident, so the forward-only scan
from page 33 reports ra_pages == 0 even though a neighbouring page was
brought in.

Keep the existing readahead assertion, but count resident neighbouring
pages on both sides of the faulted page.  This fixes the 64K-page false
failure without teaching the selftest to compute the expected readahead
window from sysfs or other implementation details.

Link: https://lore.kernel.org/20260713094319.771550-1-wangyijia.yeah@bytedance.com
Signed-off-by: Yijia Wang <wangyijia.yeah@bytedance.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions