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diff --git a/Source/WebKit2/UIProcess/linux/MemoryPressureMonitor.cpp b/Source/WebKit2/UIProcess/linux/MemoryPressureMonitor.cpp
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+++ b/Source/WebKit2/UIProcess/linux/MemoryPressureMonitor.cpp
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+/*
+ * Copyright (C) 2016 Igalia S.L.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "MemoryPressureMonitor.h"
+
+#if OS(LINUX)
+
+#include "Attachment.h"
+#include <errno.h>
+#include <fcntl.h>
+#include <mutex>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/eventfd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <wtf/CurrentTime.h>
+#include <wtf/Threading.h>
+#include <wtf/UniStdExtras.h>
+
+namespace WebKit {
+
+static const size_t notSet = static_cast<size_t>(-1);
+
+static const double s_minPollingIntervalInSeconds = 1;
+static const double s_maxPollingIntervalInSeconds = 5;
+static const double s_minUsedMemoryPercentageForPolling = 50;
+static const double s_maxUsedMemoryPercentageForPolling = 90;
+static const int s_memoryPresurePercentageThreshold = 95;
+
+static size_t lowWatermarkPages()
+{
+    FILE* file = fopen("/proc/zoneinfo", "r");
+    if (!file)
+        return notSet;
+
+    size_t low = 0;
+    bool inZone = false;
+    bool foundLow = false;
+    char buffer[128];
+    while (char* line = fgets(buffer, 128, file)) {
+        if (!strncmp(line, "Node", 4)) {
+            inZone = true;
+            foundLow = false;
+            continue;
+        }
+
+        char* token = strtok(line, " ");
+        if (!token)
+            continue;
+
+        if (!strcmp(token, "low")) {
+            if (!inZone || foundLow) {
+                low = notSet;
+                break;
+            }
+            token = strtok(nullptr, " ");
+            if (!token) {
+                low = notSet;
+                break;
+            }
+            low += atoll(token);
+            foundLow = true;
+        }
+    }
+    fclose(file);
+
+    return low;
+}
+
+static inline size_t systemPageSize()
+{
+    static size_t pageSize = 0;
+    if (!pageSize)
+        pageSize = sysconf(_SC_PAGE_SIZE);
+    return pageSize;
+}
+
+// If MemAvailable was not present in /proc/meminfo, because it's an old kernel version,
+// we can do the same calculation with the information we have from meminfo and the low watermaks.
+// See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773
+static size_t calculateMemoryAvailable(size_t memoryFree, size_t activeFile, size_t inactiveFile, size_t slabReclaimable)
+{
+    if (memoryFree == notSet || activeFile == notSet || inactiveFile == notSet || slabReclaimable == notSet)
+        return notSet;
+
+    size_t lowWatermark = lowWatermarkPages();
+    if (lowWatermark == notSet)
+        return notSet;
+
+    lowWatermark *= systemPageSize() / KB;
+
+    // Estimate the amount of memory available for userspace allocations, without causing swapping.
+    // Free memory cannot be taken below the low watermark, before the system starts swapping.
+    lowWatermark *= systemPageSize() / KB;
+    size_t memoryAvailable = memoryFree - lowWatermark;
+
+    // Not all the page cache can be freed, otherwise the system will start swapping. Assume at least
+    // half of the page cache, or the low watermark worth of cache, needs to stay.
+    size_t pageCache = activeFile + inactiveFile;
+    pageCache -= std::min(pageCache / 2, lowWatermark);
+    memoryAvailable += pageCache;
+
+    // Part of the reclaimable slab consists of items that are in use, and cannot be freed.
+    // Cap this estimate at the low watermark.
+    memoryAvailable += slabReclaimable - std::min(slabReclaimable / 2, lowWatermark);
+    return memoryAvailable;
+}
+
+static int systemMemoryUsedAsPercentage()
+{
+    FILE* file = fopen("/proc/meminfo", "r");
+    if (!file)
+        return -1;
+
+    size_t memoryAvailable, memoryTotal, memoryFree, activeFile, inactiveFile, slabReclaimable;
+    memoryAvailable = memoryTotal = memoryFree = activeFile = inactiveFile = slabReclaimable = notSet;
+    char buffer[128];
+    while (char* line = fgets(buffer, 128, file)) {
+        char* token = strtok(line, " ");
+        if (!token)
+            break;
+
+        if (!strcmp(token, "MemAvailable:")) {
+            if ((token = strtok(nullptr, " "))) {
+                memoryAvailable = atoll(token);
+                if (memoryTotal != notSet)
+                    break;
+            }
+        } else if (!strcmp(token, "MemTotal:")) {
+            if ((token = strtok(nullptr, " ")))
+                memoryTotal = atoll(token);
+            else
+                break;
+        } else if (!strcmp(token, "MemFree:")) {
+            if ((token = strtok(nullptr, " ")))
+                memoryFree = atoll(token);
+            else
+                break;
+        } else if (!strcmp(token, "Active(file):")) {
+            if ((token = strtok(nullptr, " ")))
+                activeFile = atoll(token);
+            else
+                break;
+        } else if (!strcmp(token, "Inactive(file):")) {
+            if ((token = strtok(nullptr, " ")))
+                inactiveFile = atoll(token);
+            else
+                break;
+        } else if (!strcmp(token, "SReclaimable:")) {
+            if ((token = strtok(nullptr, " ")))
+                slabReclaimable = atoll(token);
+            else
+                break;
+        }
+
+        if (memoryTotal != notSet && memoryFree != notSet && activeFile != notSet && inactiveFile != notSet && slabReclaimable != notSet)
+            break;
+    }
+    fclose(file);
+
+    if (!memoryTotal || memoryTotal == notSet)
+        return -1;
+
+    if (memoryAvailable == notSet) {
+        memoryAvailable = calculateMemoryAvailable(memoryFree, activeFile, inactiveFile, slabReclaimable);
+        if (memoryAvailable == notSet)
+            return -1;
+    }
+
+    if (memoryAvailable > memoryTotal)
+        return -1;
+
+    return ((memoryTotal - memoryAvailable) * 100) / memoryTotal;
+}
+
+static inline double pollIntervalForUsedMemoryPercentage(int usedPercentage)
+{
+    // Use a different poll interval depending on the currently memory used,
+    // to avoid polling too often when the system is under low memory usage.
+    if (usedPercentage < s_minUsedMemoryPercentageForPolling)
+        return s_maxPollingIntervalInSeconds;
+
+    if (usedPercentage >= s_maxUsedMemoryPercentageForPolling)
+        return s_minPollingIntervalInSeconds;
+
+    return s_minPollingIntervalInSeconds + (s_maxPollingIntervalInSeconds - s_minPollingIntervalInSeconds) *
+        ((usedPercentage - s_minUsedMemoryPercentageForPolling) / (s_maxUsedMemoryPercentageForPolling - s_minUsedMemoryPercentageForPolling));
+}
+
+static bool isSystemdMemoryPressureMonitorAvailable()
+{
+    int fd = open("/sys/fs/cgroup/memory/memory.pressure_level", O_CLOEXEC | O_RDONLY);
+    if (fd == -1)
+        return false;
+    close(fd);
+
+    fd = open("/sys/fs/cgroup/memory/cgroup.event_control", O_CLOEXEC | O_WRONLY);
+    if (fd == -1)
+        return false;
+    close(fd);
+
+    return true;
+}
+
+bool MemoryPressureMonitor::isEnabled()
+{
+    static std::once_flag onceFlag;
+    static bool enabled;
+    std::call_once(onceFlag, [] { enabled = !isSystemdMemoryPressureMonitorAvailable(); });
+    return enabled;
+}
+
+MemoryPressureMonitor& MemoryPressureMonitor::singleton()
+{
+    ASSERT(isEnabled());
+    static NeverDestroyed<MemoryPressureMonitor> memoryMonitor;
+    return memoryMonitor;
+}
+
+MemoryPressureMonitor::MemoryPressureMonitor()
+    : m_eventFD(eventfd(0, EFD_CLOEXEC))
+{
+    if (m_eventFD == -1)
+        return;
+
+    ThreadIdentifier threadIdentifier = createThread("MemoryPressureMonitor", [this] {
+        double pollInterval = s_maxPollingIntervalInSeconds;
+        while (true) {
+            sleep(pollInterval);
+
+            int usedPercentage = systemMemoryUsedAsPercentage();
+            if (usedPercentage == -1) {
+                WTFLogAlways("Failed to get the memory usage");
+                break;
+            }
+
+            if (usedPercentage >= s_memoryPresurePercentageThreshold) {
+                uint64_t fdEvent = 1;
+                ssize_t bytesWritten = write(m_eventFD, &fdEvent, sizeof(uint64_t));
+                if (bytesWritten != sizeof(uint64_t)) {
+                    WTFLogAlways("Error writing to MemoryPressureMonitor eventFD: %s", strerror(errno));
+                    break;
+                }
+            }
+            pollInterval = pollIntervalForUsedMemoryPercentage(usedPercentage);
+        }
+        close(m_eventFD);
+    });
+    detachThread(threadIdentifier);
+}
+
+IPC::Attachment MemoryPressureMonitor::createHandle() const
+{
+    int duplicatedHandle = dupCloseOnExec(m_eventFD);
+    if (duplicatedHandle == -1)
+        return { };
+    return IPC::Attachment(duplicatedHandle);
+}
+
+} // namespace WebKit
+
+#endif // OS(LINUX)