[Quota] Lower quota for ephemeral mode (ie. session only)

storage/browser/quota/quota_settings.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "storage/browser/quota/quota_settings.h"
 
 #include <algorithm>
 
 #include "base/metrics/histogram_macros.h"
+#include "base/rand_util.h"
 #include "base/sys_info.h"
 
 #define UMA_HISTOGRAM_MBYTES(name, sample)                                     \
   UMA_HISTOGRAM_CUSTOM_COUNTS((name), static_cast<int>((sample) / kMBytes), 1, \
                               10 * 1024 * 1024 /* 10TB */, 100)
 
 namespace storage {
 
+namespace {
+
+// Skews |value| by +/- |percent|.
+int64_t RandomizeByPercent(int64_t value, int percent) {
+  double random_percent = (base::RandDouble() - 0.5) * percent;
+  return value + (value * (random_percent / 50.0));
+}
+
+}  // anon namespace
+
 base::Optional<storage::QuotaSettings> CalculateNominalDynamicSettings(
     const base::FilePath& partition_path,
     bool is_incognito) {
   const int64_t kMBytes = 1024 * 1024;
+  const int k10Percent = 10;

[jsbell, 2017/04/04 16:23:57]

This should probably be named with respect to what it does, e.g.
kRandomizedPercentage

[michaeln, 2017/04/05 01:20:56]

Done.

 
   if (is_incognito) {
     storage::QuotaSettings settings;
-    settings.pool_size =
-        std::min(300 * kMBytes, base::SysInfo::AmountOfPhysicalMemory() / 10);
+    settings.pool_size = std::min(RandomizeByPercent(300 * kMBytes, k10Percent),

[jsbell, 2017/04/04 16:23:57]

Can we make the 300*kMBytes a constant, e.g. kMaxMemoryQuotaMBytes

[michaeln, 2017/04/05 01:20:56]

Done.

+                                  base::SysInfo::AmountOfPhysicalMemory() / 10);

[jsbell, 2017/04/04 16:23:57]

Can we make the 10 here a constant, e.g. kMemoryQuotaDivisor

[michaeln, 2017/04/05 01:20:56]

Done.

     settings.per_host_quota = settings.pool_size / 3;
+    settings.session_only_per_host_quota = settings.per_host_quota;
     settings.refresh_interval = base::TimeDelta::Max();
     return settings;
   }
 
   // The fraction of the device's storage the browser is willing to
   // use for temporary storage, this is applied after adjusting the
   // total to take os_accomodation into account.
   const double kTemporaryPoolSizeRatio = 1.0 / 3.0;  // 33%
 
   // The fraction of the device's storage the browser attempts to
@@ skipping 36 matching lines @@
   UMA_HISTOGRAM_MBYTES("Quota.OSAccomodationDelta",
                        kDefaultOSAccomodation - os_accomodation);
 
   int64_t adjusted_total = total - os_accomodation;
   int64_t pool_size = adjusted_total * kTemporaryPoolSizeRatio;
 
   settings.pool_size = pool_size;
   settings.should_remain_available = total * kShouldRemainAvailableRatio;
   settings.must_remain_available = total * kMustRemainAvailableRatio;
   settings.per_host_quota = pool_size / kPerHostTemporaryPortion;
+  settings.session_only_per_host_quota =
+      std::min(RandomizeByPercent(300 * kMBytes, k10Percent),

[cmumford, 2017/04/04 16:38:29]

This doesn't actually do what the title of issue 619927 requests since it
ignores physical memory. If that's desired then how about creating a method,
named something like CalculateEphemeralOriginQuota(), and using it here, and up
above in the incognito section?

[michaeln, 2017/04/05 01:20:56]

I've decoupled them from one another rather than linked them together.

+               settings.per_host_quota / 10);
   settings.refresh_interval = base::TimeDelta::FromSeconds(60);
   return settings;
 }
 
 }  // namespace