From 171fde15749fa87a93ff2ca4f3ee17216befe3bb Mon Sep 17 00:00:00 2001
From: Matheus <matheusuky@gmail.com>
Date: Sun, 26 May 2024 15:30:14 -0300
Subject: [PATCH] vmmcache: vmmcache_evict

---
 kernel-src/include/kernel/vmmcache.h |  3 +++
 kernel-src/mm/vmmcache.c             | 27 +++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/kernel-src/include/kernel/vmmcache.h b/kernel-src/include/kernel/vmmcache.h
index 97c436fb..598d8e4c 100644
--- a/kernel-src/include/kernel/vmmcache.h
+++ b/kernel-src/include/kernel/vmmcache.h
@@ -4,6 +4,8 @@
 #include <kernel/pmm.h>
 #include <kernel/vfs.h>
 
+extern size_t vmmcache_cachedpages;
+
 void vmmcache_init();
 int vmmcache_getpage(vnode_t *vnode, uintmax_t offset, page_t **res);
 int vmmcache_takepage(page_t *page);
@@ -11,5 +13,6 @@ int vmmcache_makedirty(page_t *page);
 int vmmcache_truncate(vnode_t *vnode, uintmax_t offset);
 int vmmcache_syncvnode(vnode_t *vnode, uintmax_t startoffset, size_t size);
 int vmmcache_sync();
+int vmmcache_evict(page_t *page);
 
 #endif
diff --git a/kernel-src/mm/vmmcache.c b/kernel-src/mm/vmmcache.c
index 6176147e..5cb210a9 100644
--- a/kernel-src/mm/vmmcache.c
+++ b/kernel-src/mm/vmmcache.c
@@ -13,6 +13,7 @@ static page_t **table;
 static thread_t *writerthread;
 static semaphore_t sync;
 static pollheader_t syncpollheader;
+size_t vmmcache_cachedpages;
 
 #define HOLD_LOCK() \
 	MUTEX_ACQUIRE(&mutex, false);
@@ -66,6 +67,7 @@ static void putpage(page_t *page) {
 		page->backing->pages->vnodeprev = page;
 
 	page->backing->pages = page;
+	++vmmcache_cachedpages;
 }
 
 // assumes lock is held
@@ -95,6 +97,7 @@ static void removepage(page_t *page) {
 
 	page->vnodenext = NULL;
 	page->vnodeprev = NULL;
+	--vmmcache_cachedpages;
 }
 
 int vmmcache_getpage(vnode_t *vnode, uintmax_t offset, page_t **res) {
@@ -178,6 +181,30 @@ int vmmcache_getpage(vnode_t *vnode, uintmax_t offset, page_t **res) {
 	return 0;
 }
 
+// removes a page from the cache AND turns it into anonymous memory
+int vmmcache_evict(page_t *page) {
+	HOLD_LOCK();
+	if (page->refcount > 1) {
+		RELEASE_LOCK();
+		return EAGAIN;
+	}
+	__assert(page->refcount == 1);
+	__assert((page->flags & PAGE_FLAGS_DIRTY) == 0);
+
+	if ((page->flags & PAGE_FLAGS_TRUNCATED) == 0) {
+		// the page needs to be removed from the cache to continue
+		removepage(page);
+	}
+
+	page->flags = 0;
+	page->backing = NULL;
+	page->offset = 0;
+
+	RELEASE_LOCK();
+	return 0;
+}
+
+// removes a page from the cache *but doesn't do anything to it*
 int vmmcache_takepage(page_t *page) {
 	HOLD_LOCK();
 	// someone called vmmcache_getpage() and got this page while the lock wasn't held