Revert "drop page heap lock when returning memory back to kernel"

This reverts commit be3da70298.

There are reports of crashes and false-positive OOMs from this
patch. Crashes under aggressive decommit mode are understood, but I
have yet to get confirmations whether false-positive OOMs were seen
under aggressive decommit or not. Thus lets revert for now.

Updates issue #1227 and issue #1204.

src/page_heap.cc

@@ -241,22 +241,12 @@ void PageHeap::CommitSpan(Span* span) {
   stats_.total_commit_bytes += (span->length << kPageShift);
 }
 
-bool PageHeap::TryDecommitWithoutLock(Span* span) {
+bool PageHeap::DecommitSpan(Span* span) {
   ++stats_.decommit_count;
-  ASSERT(span->location == Span::ON_NORMAL_FREELIST);
-  span->location = Span::IN_USE;
 
-  Static::pageheap_lock()->Unlock();
   bool rv = TCMalloc_SystemRelease(reinterpret_cast<void*>(span->start << kPageShift),
                                    static_cast<size_t>(span->length << kPageShift));
-  Static::pageheap_lock()->Lock();
-
-  // We're not really on any free list at this point, but lets
-  // indicate if we're returned or not.
-  span->location = Span::ON_NORMAL_FREELIST;
-
   if (rv) {
-    span->location = Span::ON_RETURNED_FREELIST;
     stats_.committed_bytes -= span->length << kPageShift;
     stats_.total_decommit_bytes += (span->length << kPageShift);
   }
@@ -330,19 +320,15 @@ Span* PageHeap::CheckAndHandlePreMerge(Span* span, Span* other) {
   if (other == NULL) {
     return other;
   }
-
-  // If we're in aggressive decommit mode and span is decommitted,
-  // then we try to decommit adjacent span. We also remove from it's
-  // free list as part of that.
+  // if we're in aggressive decommit mode and span is decommitted,
+  // then we try to decommit adjacent span.
   if (aggressive_decommit_ && other->location == Span::ON_NORMAL_FREELIST
       && span->location == Span::ON_RETURNED_FREELIST) {
-    if (ReleaseSpan(other) != 0) {
-      return other;
-    }
+    bool worked = DecommitSpan(other);
+    if (!worked) {
       return NULL;
     }
-
-  if (other->location != span->location) {
+  } else if (other->location != span->location) {
     return NULL;
   }
 
@@ -374,7 +360,7 @@ void PageHeap::MergeIntoFreeList(Span* span) {
   const Length n = span->length;
 
   if (aggressive_decommit_ && span->location == Span::ON_NORMAL_FREELIST) {
-    if (TryDecommitWithoutLock(span)) {
+    if (DecommitSpan(span)) {
       span->location = Span::ON_RETURNED_FREELIST;
     }
   }
@@ -481,35 +467,18 @@ void PageHeap::IncrementalScavenge(Length n) {
   }
 }
 
-Length PageHeap::ReleaseSpan(Span* span) {
-  // We're dropping very important and otherwise contended
-  // pageheap_lock around call to potentially very slow syscall to
-  // release pages. Those syscalls can be slow even with "advanced"
-  // things such as MADV_FREE and its better equivalents, because they
-  // have to walk actual page tables, and we sometimes deal with large
-  // spans, which sometimes takes lots of time to walk. Plus Linux
-  // grabs per-address space mmap_sem lock which could be extremely
-  // contended at times. So it is best if we avoid holding one
-  // contended lock while waiting for another.
-  //
-  // Note, we set span location to in-use, because our span could be found via
-  // pagemap in e.g. MergeIntoFreeList while we're not holding the lock. By
-  // marking it in-use we prevent this possibility. So span is removed from free
-  // list and marked "unmergable" and that guarantees safety during unlock-ful
-  // release.
-  ASSERT(span->location == Span::ON_NORMAL_FREELIST);
-  RemoveFromFreeList(span);
+Length PageHeap::ReleaseSpan(Span* s) {
+  ASSERT(s->location == Span::ON_NORMAL_FREELIST);
 
-  Length n = span->length;
-  if (TryDecommitWithoutLock(span)) {
-    span->location = Span::ON_RETURNED_FREELIST;
-  } else {
-    n = 0; // Mark that we failed to return.
-    span->location = Span::ON_NORMAL_FREELIST;
+  if (DecommitSpan(s)) {
+    RemoveFromFreeList(s);
+    const Length n = s->length;
+    s->location = Span::ON_RETURNED_FREELIST;
+    MergeIntoFreeList(s);  // Coalesces if possible.
+    return n;
   }
 
-  MergeIntoFreeList(span);  // Coalesces if possible.
-  return n;
+  return 0;
 }
 
 Length PageHeap::ReleaseAtLeastNPages(Length num_pages) {

src/page_heap.h

@@ -314,7 +314,7 @@ class PERFTOOLS_DLL_DECL PageHeap {
   void CommitSpan(Span* span);
 
   // Decommit the span.
-  bool TryDecommitWithoutLock(Span* span);
+  bool DecommitSpan(Span* span);
 
   // Prepends span to appropriate free list, and adjusts stats.
   void PrependToFreeList(Span* span);
@@ -326,12 +326,12 @@ class PERFTOOLS_DLL_DECL PageHeap {
   // IncrementalScavenge(n) is called whenever n pages are freed.
   void IncrementalScavenge(Length n);
 
-  // Attempts to decommit 'span' and move it to the returned freelist.
+  // Attempts to decommit 's' and move it to the returned freelist.
   //
   // Returns the length of the Span or zero if release failed.
   //
-  // REQUIRES: 'span' must be on the NORMAL freelist.
-  Length ReleaseSpan(Span *span);
+  // REQUIRES: 's' must be on the NORMAL freelist.
+  Length ReleaseSpan(Span *s);
 
   // Checks if we are allowed to take more memory from the system.
   // If limit is reached and allowRelease is true, tries to release

src/tests/page_heap_test.cc

@@ -11,19 +11,15 @@
 
 #include <memory>
 
-#include "base/logging.h"
-#include "base/spinlock.h"
-#include "common.h"
 #include "page_heap.h"
 #include "system-alloc.h"
-#include "static_vars.h"
+#include "base/logging.h"
+#include "common.h"
 
 DECLARE_int64(tcmalloc_heap_limit_mb);
 
 namespace {
 
-using tcmalloc::Static;
-
 // The system will only release memory if the block size is equal or hight than
 // system page size.
 static bool HaveSystemRelease =
@@ -48,7 +44,6 @@ static void CheckStats(const tcmalloc::PageHeap* ph,
 
 static void TestPageHeap_Stats() {
   std::unique_ptr<tcmalloc::PageHeap> ph(new tcmalloc::PageHeap());
-  SpinLockHolder h(Static::pageheap_lock());
 
   // Empty page heap
   CheckStats(ph.get(), 0, 0, 0);
@@ -84,8 +79,6 @@ static void AllocateAllPageTables() {
   // Make a separate PageHeap from the main test so the test can start without
   // any pages in the lists.
   std::unique_ptr<tcmalloc::PageHeap> ph(new tcmalloc::PageHeap());
-  SpinLockHolder h(Static::pageheap_lock());
-
   tcmalloc::Span *spans[kNumberMaxPagesSpans * 2];
   for (int i = 0; i < kNumberMaxPagesSpans; ++i) {
     spans[i] = ph->New(kMaxPages);
@@ -107,7 +100,6 @@ static void TestPageHeap_Limit() {
   AllocateAllPageTables();
 
   std::unique_ptr<tcmalloc::PageHeap> ph(new tcmalloc::PageHeap());
-  SpinLockHolder h(Static::pageheap_lock());
 
   CHECK_EQ(kMaxPages, 1 << (20 - kPageShift));
 
@@ -196,8 +188,6 @@ static void TestPageHeap_Limit() {
 }  // namespace
 
 int main(int argc, char **argv) {
-  Static::InitStaticVars();
-
   TestPageHeap_Stats();
   TestPageHeap_Limit();
   printf("PASS\n");