On Mon, Sep 21, 2020 at 09:43:17AM +0800, Yafang Shao wrote: > Our users reported that there're some random latency spikes when their RT > process is running. Finally we found that latency spike is caused by > FADV_DONTNEED. Which may call lru_add_drain_all() to drain LRU cache on > remote CPUs, and then waits the per-cpu work to complete. The wait time > is uncertain, which may be tens millisecond. > That behavior is unreasonable, because this process is bound to a > specific CPU and the file is only accessed by itself, IOW, there should > be no pagecache pages on a per-cpu pagevec of a remote CPU. That > unreasonable behavior is partially caused by the wrong comparation of the > number of invalidated pages and the number of the target. For example, > if (count < (end_index - start_index + 1)) > The count above is how many pages were invalidated in the local CPU, and > (end_index - start_index + 1) is how many pages should be invalidated. > The usage of (end_index - start_index + 1) is incorrect, because they > are virtual addresses, which may not mapped to pages. We'd better use > inode->i_data.nrpages as the target. > How does that work if the invalidation is for a subset of the file? -- Mel Gorman SUSE Labs
