[Experiment] purge-and-suspend

third_party/WebKit/Source/platform/heap/HeapPage.cpp

Index: third_party/WebKit/Source/platform/heap/HeapPage.cpp
diff --git a/third_party/WebKit/Source/platform/heap/HeapPage.cpp b/third_party/WebKit/Source/platform/heap/HeapPage.cpp
index b7da90ae531826a4df862d5d38dc523e66d1271c..67900c103c27db88c1396694949aa7cc7b43d5af 100644
--- a/third_party/WebKit/Source/platform/heap/HeapPage.cpp
+++ b/third_party/WebKit/Source/platform/heap/HeapPage.cpp
@@ -1201,10 +1201,7 @@ void NormalPage::sweep()
         if (startOfGap != headerAddress) {
             pageArena->addToFreeList(startOfGap, headerAddress - startOfGap);
 #if !ENABLE(ASSERT) && !defined(LEAK_SANITIZER) && !defined(ADDRESS_SANITIZER)
-            // Discarding pages increases page faults and may regress performance.
-            // So we enable this only on low-RAM devices.
-            if (ProcessHeap::isLowEndDevice())
-                discardPages(startOfGap + sizeof(FreeListEntry), headerAddress);
+            discardPages(startOfGap + sizeof(FreeListEntry), headerAddress);

[sof, 2016/07/07 09:35:19]

Why drop the check for low-end devices?

[tasak, 2016/07/08 03:56:45]

To reduce resident_set_bytes, pss, or private_dirty.

However, I agree that the change is a quick hack.
I will revert this change. Instead, I will add some method / function for
discarding oilpan's unused pages which will be invoked when memory pressure is
notified.

[sof, 2016/07/08 07:14:29]

That would be better; what's here now will seriously upset paging behavior (and
was an quick & expedient change put in to counter an RSS regression seen on
lower-end devices.)

[tasak, 2016/07/19 08:22:51]

I think, I need, Oilpan::discardUnusedPages or something. I would like to
discuss with haraken@.

[haraken, 2016/07/19 20:20:22]

This makes sense.

Currently discardPages() is called only on low-end devices
(https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/heap/...)
but we can change it so that discardPages() is also called in a GC triggered by
memory pressures.

 #endif
         }
         header->unmark();
@@ -1215,8 +1212,7 @@ void NormalPage::sweep()
     if (startOfGap != payloadEnd()) {
         pageArena->addToFreeList(startOfGap, payloadEnd() - startOfGap);
 #if !ENABLE(ASSERT) && !defined(LEAK_SANITIZER) && !defined(ADDRESS_SANITIZER)
-        if (ProcessHeap::isLowEndDevice())
-            discardPages(startOfGap + sizeof(FreeListEntry), payloadEnd());
+        discardPages(startOfGap + sizeof(FreeListEntry), payloadEnd());
 #endif
     }