Change mode of operation for mmap_file (see readme)

1 files changed, 16 insertions, 1 deletions

diff --git a/README.md b/README.md
index 282054c..b74eeef 100644
--- a/README.md
+++ b/README.md
@@ -93,7 +93,22 @@ running the tests):
 
 ### Things to design
 
-* Cache architecture
+* Cache architecture :
+  - A RAM file is basically a bunch of pages that contain the data (rather than a segment of
+    malloc()'ed memory)
+  - A framebuffer device is basically a bunch of pages at a fixed hardware location, that cannot
+    grow
+  - In the two previous cases, the pages are never freed : they are not a cache, they are the
+    data itself.
+  - In the case of an on-disk file, the pages are a copy of the file's data that is originally
+    on-disk, and we might want to free these pages even while a process is using them, because
+    we can always reload them from the disk.
+  - An on-disk file with a page cache must be aware of all the places where the page is mapped,
+    so that it can unmap it when reclaiming pages.
+  - Simpler model : cached pages cannot be freed while the file is open with `FM_MMAP`
+* Reclaiming physical memory :
+  - Freeing some cached stuff, ie swapping pages from mmap regions
+  - Swapping pages from processes non-mmap regions (ie real data regions)
 * IPC
 * How does a process exit, what does it do, how do processes synchronize ?
 * Have several threads in a single process