I’m not familiar with JVM things and what DMA is there, but usually when people talk about the OS page cache, they mean the in-memory file cache stored by the kernel. This means that if you read or write to a page in the cache, you’d be accessing memory instead of disk.
The alternative is to open your file with O_DIRECT, which makes your reads/writes always interact with the storage system and bypasses the page cache.
The alternative is to open your file with O_DIRECT, which makes your reads/writes always interact with the storage system and bypasses the page cache.