[PATCH 3/9] readahead: auto detection of sequential mmap reads

Auto-detect sequential mmap reads and do sync/async readahead for them. The sequential mmap readahead will be triggered when - sync readahead: it's a major fault and (prev_offset==offset-1); - async readahead: minor fault on PG_readahead page with valid readahead state. It's a bit conservative to

[PATCH 3/9] readahead: auto detection of sequential mmap reads

Auto-detect sequential mmap reads and do sync/async readahead for them. The sequential mmap readahead will be triggered when - sync readahead: it's a major fault and (prev_offset==offset-1); - async readahead: minor fault on PG_readahead page with valid readahead state. It's a bit conservative to