RFR: 8271195: Use largest available large page size smaller than LargePageSizeInBytes when available [v7]

[Stefan Johansson]

On Mon, 21 Feb 2022 11:30:38 GMT, Swati Sharma <duke at openjdk.java.net> wrote:

>> Hi Team,
>> 
>> In this patch I have fixed two issues related to large pages, following is the summary of changes :-
>> 
>> 1. Patch fixes existing large page allocation functionality where if a commit over 1GB pages fails allocation should happen over next small page size i.e. 2M where as currently its happening over 4kb pages resulting into significant TLB miss penalty.
>> Patch includes new JTREG Test case covering various scenarios for checking the correct explicit page allocation according ​to the 1G, 2M, 4K priority.
>> 2. While attempting commit over larger pages we first try to reserve requested bytes over the virtual address space, in case commit to large page fails we should be un reserving entire reservation to avoid leaving any leaks in virtual address space.
>> 
>> ​
>> Please find below the performance data with and without patch for the JMH benchmark included with the patch.
>> 
>> ![image](https://user-images.githubusercontent.com/96874289/152189587-4822a4ca-f5e2-4621-b405-0da941485143.png)
>> 
>> 
>> Please review and provide your valuable comments.
>> 
>> 
>> 
>> Thanks,
>> Swati Sharma
>> Runtime Software Development Engineer 
>> Intel
>
> Swati Sharma has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8271195: Review comments are resolved

I'm currently running the latest test through our testing to make sure everything is fine.

Sorry for the many suggestions, I didn't expect it to be so many. Please take another look through the code as well, I might have missed some additional places where spaces should be added to use the same format as the rest of the file and other tests.

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 61:

> 59: 
> 60:     private static final String DIR_HUGE_PAGES = "/sys/kernel/mm/hugepages/";
> 61:     private static final int HEAP_SIZE_IN_KB = 1 * 1024 *1024;

Suggestion:

    private static final int HEAP_SIZE_IN_KB = 1 * 1024 * 1024;

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 71:

> 69:     private static String errorMessage = null;
> 70: 
> 71:     private static final int MAX_NUMBER_OF_PAGESIZE=64;

Suggestion:

    private static final int MAX_NUMBER_OF_PAGESIZE = 64;

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 80:

> 78:         try {
> 79:             doSetup();
> 80:             for (int i = MAX_NUMBER_OF_PAGESIZE-1;i > vmPageSizeIndex;i--) {

Suggestion:

            for (int i = MAX_NUMBER_OF_PAGESIZE - 1; i > vmPageSizeIndex; i--) {

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 87:

> 85:             }
> 86:         } catch(Exception e) {
> 87:            System.out.println("Exception"+e);

Suggestion:

           System.out.println("Exception" + e);

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 109:

> 107:         else
> 108:            return Integer.toString(sizeInBytes/g)+"G";
> 109:     }

Suggestion:

    private static int requiredPageCount(int index) {
        int pageSizeInKB = 1 << (index - 10);
        return HEAP_SIZE_IN_KB / pageSizeInKB;
    }

    private static String sizeFromIndex(int index) {
        int k = 1024;
        int m = 1024 * 1024;
        int g = 1024 * 1024 * 1024;
        int sizeInBytes = 1 << index;
        if (sizeInBytes < m)
           return Integer.toString(sizeInBytes / k) + "K";
        if(sizeInBytes < g)
           return Integer.toString(sizeInBytes / m) + "M";
        else
           return Integer.toString(sizeInBytes / g) + "G";
    }

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 150:

> 148:                 System.out.println("No Pages configured for "+pageSize+"kB");
> 149:             }
> 150:             int index = Integer.numberOfTrailingZeros(Integer.parseInt(pageSize)*1024);

Suggestion:

            int availablePages = checkAndReadFile(DIR_HUGE_PAGES + pageSizeFileName + "/free_hugepages", pageSize);
            if (availablePages == 0) {
                System.out.println("No Pages configured for " + pageSize + "kB");
            }
            int index = Integer.numberOfTrailingZeros(Integer.parseInt(pageSize) * 1024);

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 171:

> 169:         OutputAnalyzer output = new OutputAnalyzer(pb.start());
> 170:         output.shouldHaveExitValue(0);
> 171:         for (int i = index;i >= vmPageSizeIndex;i--) {

Suggestion:

        for (int i = index; i >= vmPageSizeIndex; i--) {

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 179:

> 177:                        continue;
> 178:                     }
> 179:                     errorMessage += "TestCase Failed for "+size+" page allocation\n";

Suggestion:

                    errorMessage += "TestCase Failed for " + size + " page allocation\n";

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 181:

> 179:                     errorMessage += "TestCase Failed for "+size+" page allocation\n";
> 180:                 } else {
> 181:                     System.out.println("TestCase Passed for pagesize: "+pageSize+", allocated pagesize:"+size);

Suggestion:

                    System.out.println("TestCase Passed for pagesize: " + pageSize + ", allocated pagesize:" + size);

test/hotspot/jtreg/runtime/os/TestExplicitPageAllocation.java line 188:

> 186:         }
> 187: 
> 188:         if (errorMessage!=null) {

Suggestion:

        if (errorMessage != null) {

-------------

Changes requested by sjohanss (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/7326