[Experiment] purge-and-suspend

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1183 matching lines @@
             header->finalize(payload, payloadSize);
             // This memory will be added to the freelist. Maintain the invariant
             // that memory on the freelist is zero filled.
             SET_MEMORY_INACCESSIBLE(headerAddress, size);
             headerAddress += size;
             continue;
         }
         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();
         headerAddress += size;
         markedObjectSize += size;
         startOfGap = headerAddress;
     }
     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
     }
 
     if (markedObjectSize)
         pageArena->getThreadState()->increaseMarkedObjectSize(markedObjectSize);
 }
 
 void NormalPage::makeConsistentForGC()
 {
     size_t markedObjectSize = 0;
@@ skipping 386 matching lines @@
 
     m_hasEntries = true;
     size_t index = hash(address);
     ASSERT(!(index & 1));
     Address cachePage = roundToBlinkPageStart(address);
     m_entries[index + 1] = m_entries[index];
     m_entries[index] = cachePage;
 }
 
 } // namespace blink