Page Cache
Page cache is a particular kernel buffer used specifically to cache file-backed data (regular files, some filesystem data) in RAM.
Why is it called a page cache?
Because the kernel is caching file data as memory pages (the same fixed-size chunks the VM system manages).
The page cache does not exist in l1/l2 cache
I lives in main memory (RAM) as normal physical pages that the kernel uses to cache files contents.
how does the DMA know where to write into?
DMA doesn’t “figure it out” by itself — the OS + device driver tell it exactly where to write, by programming the device with addresses.