Disk Cache: Lower the definition of a loaded system from

10 pending operations to 5.

Data from the Beta channel shows that for all group sizes
except one, the 99.90% cutoff of number of pending
operations falls below 5 (in fact, below 3).

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/164355

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@23120 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 19 insertions, 15 deletions

diff --git a/net/disk_cache/backend_impl.cc b/net/disk_cache/backend_impl.cc
index 506ab22..5af790f 100644
--- a/net/disk_cache/backend_impl.cc
+++ b/net/disk_cache/backend_impl.cc
@@ -797,7 +797,10 @@ void BackendImpl::TooMuchStorageRequested(int32 size) {
 
 bool BackendImpl::IsLoaded() const {
   CACHE_UMA(COUNTS, "PendingIO", GetSizeGroup(), num_pending_io_);
-  return num_pending_io_ > 10;
+  if (user_flags_ & kNoLoadProtection)
+    return false;
+
+  return num_pending_io_ > 5;
 }
 
 std::string BackendImpl::HistogramName(const char* name, int experiment) const {
@@ -1589,10 +1592,7 @@ bool BackendImpl::CheckIndex() {
 
   AdjustMaxCacheSize(data_->header.table_len);
 
-  // We need to avoid integer overflows.
-  DCHECK(max_size_ < kint32max - kint32max / 10);
-  if (data_->header.num_bytes < 0 ||
-      data_->header.num_bytes > max_size_ + max_size_ / 10) {
+  if (data_->header.num_bytes < 0) {
     LOG(ERROR) << "Invalid cache (current) size";
     return false;
   }
diff --git a/net/disk_cache/backend_impl.h b/net/disk_cache/backend_impl.h
index 242c0c5..a2dd0c6 100644
--- a/net/disk_cache/backend_impl.h
+++ b/net/disk_cache/backend_impl.h
@@ -19,12 +19,13 @@
 namespace disk_cache {
 
 enum BackendFlags {
-  kMask = 1,
-  kMaxSize = 1 << 1,
-  kUnitTestMode = 1 << 2,
-  kUpgradeMode = 1 << 3,
-  kNewEviction = 1 << 4,
-  kNoRandom = 1 << 5
+  kMask = 1,                    // A mask (for the index table) was specified.
+  kMaxSize = 1 << 1,            // A maximum size was provided.
+  kUnitTestMode = 1 << 2,       // We are modifying the behavior for testing.
+  kUpgradeMode = 1 << 3,        // This is the upgrade tool (dump).
+  kNewEviction = 1 << 4,        // Use of new eviction was specified.
+  kNoRandom = 1 << 5,           // Don't add randomness to the behavior.
+  kNoLoadProtection = 1 << 6    // Don't act conservatively under load.
 };
 
 // This class implements the Backend interface. An object of this
diff --git a/net/disk_cache/stress_cache.cc b/net/disk_cache/stress_cache.cc
index b2b60e4..7b5912c 100644
--- a/net/disk_cache/stress_cache.cc
+++ b/net/disk_cache/stress_cache.cc
@@ -25,6 +25,7 @@
 #include "base/string_util.h"
 #include "base/thread.h"
 #include "net/base/io_buffer.h"
+#include "net/disk_cache/backend_impl.h"
 #include "net/disk_cache/disk_cache.h"
 #include "net/disk_cache/disk_cache_test_util.h"
 
@@ -77,10 +78,11 @@ void StressTheCache(int iteration) {
   int cache_size = 0x800000;  // 8MB
   std::wstring path = GetCachePath();
   path.append(L"_stress");
-  disk_cache::Backend* cache = disk_cache::CreateCacheBackend(path, false,
-                                                              cache_size,
-                                                              net::DISK_CACHE);
-  if (NULL == cache) {
+  disk_cache::BackendImpl* cache = new disk_cache::BackendImpl(path);
+  cache->SetFlags(disk_cache::kNoLoadProtection | disk_cache::kNoRandom);
+  cache->SetMaxSize(cache_size);
+  cache->SetType(net::DISK_CACHE);
+  if (!cache->Init()) {
     printf("Unable to initialize cache.\n");
     return;
   }
@@ -123,6 +125,7 @@ void StressTheCache(int iteration) {
 
     if (!(i % 100))
       printf("Entries: %d    \r", i);
+    MessageLoop::current()->RunAllPending();
   }
 }