Purge browser cache for dom storage in a smarter way

content/browser/dom_storage/dom_storage_area.cc

 // Copyright 2013 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 "content/browser/dom_storage/dom_storage_area.h"
 
 #include <algorithm>
 #include <cctype>  // for std::isalnum
 
 #include "base/bind.h"
@@ skipping 285 matching lines @@
   }
   map_ = new DOMStorageMap(kPerStorageAreaQuota +
                            kPerStorageAreaOverQuotaAllowance);
   if (backing_) {
     is_initial_import_done_ = false;
     backing_->Reset();
     backing_->DeleteFiles();
   }
 }
 
+void DOMStorageArea::TrimDatabase() {
+  if (backing_)

[michaeln, 2016/05/09 21:50:31]

There are some complications that i think make this problematic?

The db is used on two different 'sequences'. The initial import of data is
performed on the 'primary' sequence. Commits are the performed on the 'commit'
sequence. And the db can be reset on the 'primary' sequence when there are no
commits in flight.

A possible simplification to sidestep complexity stemming from that is to trim
the caches ever time we touch the db (see other comments in this file). 

Or consider leaving this part out for now.

[ssid, 2016/05/10 02:04:15]

Thanks, I didn't realize this issue.
Yes, post task might be overkill here and we are now clearing at commit, so i
removed this part.

+    backing_->TrimDatabase();
+}
+
 void DOMStorageArea::PurgeMemory() {
   DCHECK(!is_shutdown_);
   // Purging sessionStorage is not supported; it won't work with FastClear.
   DCHECK(!session_storage_backing_.get());
   if (!is_initial_import_done_ ||  // We're not using any memory.
       !backing_.get() ||  // We can't purge anything.
       HasUncommittedChanges())  // We leave things alone with changes pending.
     return;
 
   // Drop the in memory cache, we'll reload when needed.
@@ skipping 47 matching lines @@
 }
 
 void DOMStorageArea::InitialImportIfNeeded() {
   if (is_initial_import_done_)
     return;
 
   DCHECK(backing_.get());
 
   base::TimeTicks before = base::TimeTicks::Now();
   DOMStorageValuesMap initial_values;
   backing_->ReadAllValues(&initial_values);

[michaeln, 2016/05/09 21:50:31]

so maybe call TrimDatabase() here

[ssid, 2016/05/10 02:04:15]

Done. Made the trim non-aggressive in database.cc.

   map_->SwapValues(&initial_values);
   is_initial_import_done_ = true;
   base::TimeDelta time_to_import = base::TimeTicks::Now() - before;
   UMA_HISTOGRAM_TIMES("LocalStorage.BrowserTimeToPrimeLocalStorage",
                       time_to_import);
 
   size_t local_storage_size_kb = map_->bytes_used() / 1024;
   // Track localStorage size, from 0-6MB. Note that the maximum size should be
   // 5MB, but we add some slop since we want to make sure the max size is always
   // above what we see in practice, since histograms can't change.
@@ skipping 84 matching lines @@
       base::Bind(&DOMStorageArea::CommitChanges, this,
                  base::Owned(commit_batch_.release())));
   ++commit_batches_in_flight_;
   DCHECK(success);
 }
 
 void DOMStorageArea::CommitChanges(const CommitBatch* commit_batch) {
   // This method executes on the commit sequence.
   DCHECK(task_runner_->IsRunningOnCommitSequence());
   backing_->CommitChanges(commit_batch->clear_all_first,
                           commit_batch->changed_values);

[michaeln, 2016/05/09 21:50:31]

and maybe call TrimMemory() here

[ssid, 2016/05/10 02:04:15]

Done.

   // TODO(michaeln): what if CommitChanges returns false (e.g., we're trying to
   // commit to a DB which is in an inconsistent state?)
   task_runner_->PostTask(
       FROM_HERE,
       base::Bind(&DOMStorageArea::OnCommitComplete, this));
 }
 
 void DOMStorageArea::OnCommitComplete() {
   // We're back on the primary sequence in this method.
   DCHECK(task_runner_->IsRunningOnPrimarySequence());
@@ skipping 18 matching lines @@
         commit_batch_->clear_all_first,
         commit_batch_->changed_values);
     DCHECK(success);
   }
   commit_batch_.reset();
   backing_.reset();
   session_storage_backing_ = NULL;
 }
 
 }  // namespace content