From d5ad762913429ae34478222a0c87199be0709439 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Axel=20D=C3=B6rfler?= <axeld@pinc-software.de>
Date: Thu, 30 Apr 2009 15:53:41 +0000
Subject: [PATCH] Fixed several problems of the prefetching code: * Did claim
 to have reserved pages when calling vm_page_allocate_page(), but   didn't
 have any (copy&paste bug). We cannot use it without reserved pages,   as we
 need to call vm_page_allocate_page() with a cache locked. * No longer use
 low_resource_state() to determine whether to precache or not,   but use the
 new vm_page_num_used_pages() instead. * Also don't (try to) precache when the
 cache already has more than 2/3 of its   pages to safe some unnecessary work.
 * The size to precache was limited to the file size incorrectly. * When
 precaching failed, the cache reference was not released. * The precaching
 started one page too late, causing bug #3835. * Reenabled precaching.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@30515 a95241bf-73f2-0310-859d-f6bbb57e9c96
---
 src/system/kernel/cache/file_cache.cpp | 33 +++++++++++++++-----------
 src/system/kernel/vm/vm.cpp            |  6 +----
 2 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/src/system/kernel/cache/file_cache.cpp b/src/system/kernel/cache/file_cache.cpp
index cc7960d7fc..3716c76b55 100644
--- a/src/system/kernel/cache/file_cache.cpp
+++ b/src/system/kernel/cache/file_cache.cpp
@@ -164,17 +164,16 @@ PrecacheIO::Start()
 	uint32 vecCount = 0;
 	uint32 i = 0;
 	for (size_t pos = 0; pos < fSize; pos += B_PAGE_SIZE) {
-		vm_page* page = fPages[i++] = vm_page_allocate_page(
-			PAGE_STATE_FREE, true);
+		vm_page* page = vm_page_allocate_page(PAGE_STATE_FREE, true);
 		if (page == NULL)
 			break;
 
-		fBusyConditions[i - 1].Publish(page, "page");
-
+		fBusyConditions[i].Publish(page, "page");
 		fCache->InsertPage(page, fOffset + pos);
 
 		add_to_iovec(fVecs, vecCount, fPageCount,
 			page->physical_page_number * B_PAGE_SIZE, B_PAGE_SIZE);
+		fPages[i++] = page;
 	}
 
 	if (i != fPageCount) {
@@ -903,10 +902,8 @@ file_cache_control(const char *subsystem, uint32 function, void *buffer,
 extern "C" void
 cache_prefetch_vnode(struct vnode *vnode, off_t offset, size_t size)
 {
-	if (low_resource_state(B_KERNEL_RESOURCE_PAGES) != B_NO_LOW_RESOURCE) {
-		// don't do anything if we don't have the resources left
+	if (size == 0)
 		return;
-	}
 
 	vm_cache *cache;
 	if (vfs_get_vnode_cache(vnode, &cache, false) != B_OK)
@@ -915,12 +912,17 @@ cache_prefetch_vnode(struct vnode *vnode, off_t offset, size_t size)
 	file_cache_ref *ref = ((VMVnodeCache*)cache)->FileCacheRef();
 	off_t fileSize = cache->virtual_end;
 
-	if (offset >= fileSize) {
+	if (offset + size > fileSize)
+		size = fileSize - offset;
+	size_t reservePages = size / B_PAGE_SIZE;
+
+	// Don't do anything if we don't have the resources left, or the cache
+	// already contains more than 2/3 of its pages
+	if (offset >= fileSize || vm_page_num_unused_pages() < 2 * reservePages
+		|| 3 * cache->page_count > 2 * fileSize / B_PAGE_SIZE) {
 		cache->ReleaseRef();
 		return;
 	}
-	if (offset + size > fileSize)
-		size = offset - fileSize;
 
 	// "offset" and "size" are always aligned to B_PAGE_SIZE,
 	offset &= ~(B_PAGE_SIZE - 1);
@@ -929,7 +931,9 @@ cache_prefetch_vnode(struct vnode *vnode, off_t offset, size_t size)
 	size_t bytesToRead = 0;
 	off_t lastOffset = offset;
 
-	AutoLocker<VMCache> locker(cache);
+	vm_page_reserve_pages(reservePages);
+
+	cache->Lock();
 
 	while (true) {
 		// check if this page is already in memory
@@ -950,7 +954,7 @@ cache_prefetch_vnode(struct vnode *vnode, off_t offset, size_t size)
 				= new(std::nothrow) PrecacheIO(ref, lastOffset, bytesToRead);
 			if (io == NULL || io->Init() != B_OK || io->Start() != B_OK) {
 				delete io;
-				return;
+				break;
 			}
 
 			bytesToRead = 0;
@@ -961,10 +965,11 @@ cache_prefetch_vnode(struct vnode *vnode, off_t offset, size_t size)
 			break;
 		}
 
-		lastOffset = offset + B_PAGE_SIZE;
+		lastOffset = offset;
 	}
 
-	cache->ReleaseRefLocked();
+	cache->ReleaseRefAndUnlock();
+	vm_page_unreserve_pages(reservePages);
 }
 
 
diff --git a/src/system/kernel/vm/vm.cpp b/src/system/kernel/vm/vm.cpp
index 6d4d9309b4..4b6ace396b 100644
--- a/src/system/kernel/vm/vm.cpp
+++ b/src/system/kernel/vm/vm.cpp
@@ -2362,16 +2362,12 @@ _vm_map_file(team_id team, const char* name, void** _address,
 
 	cache->Unlock();
 
-#if 0
-// TODO: Fix ticket #3835 before enabling pre-fetching
-// http://dev.haiku-os.org/ticket/3835
 	if (status == B_OK) {
 		// TODO: this probably deserves a smarter solution, ie. don't always
-		// prefetch stuff
+		// prefetch stuff, and also, probably don't trigger it at this place.
 		cache_prefetch_vnode(vnode, offset, min_c(size, 10LL * 1024 * 1024));
 			// prefetches at max 10 MB starting from "offset"
 	}
-#endif
 
 	if (status != B_OK)
 		return status;