base/SOURCES/glibc-rh1284959-1.patch

Description: Makes trimming work consistently across arenas.
Author: Mel Gorman <mgorman@suse.de>
Origin: git://sourceware.org/git/glibc.git
Bug-RHEL: N/A
Bug-Fedora: N/A
Bug-Upstream: #17195
Upstream status: committed

Part of commit 8a35c3fe122d49ba76dff815b3537affb5a50b45 is also included
to allow the use of ALIGN_UP within malloc/arena.c.

commit c26efef9798914e208329c0e8c3c73bb1135d9e3
Author: Mel Gorman <mgorman@suse.de>
Date:   Thu Apr 2 12:14:14 2015 +0530

    malloc: Consistently apply trim_threshold to all heaps [BZ #17195]
    
    Trimming heaps is a balance between saving memory and the system overhead
    required to update page tables and discard allocated pages. The malloc
    option M_TRIM_THRESHOLD is a tunable that users are meant to use to decide
    where this balance point is but it is only applied to the main arena.
    
    For scalability reasons, glibc malloc has per-thread heaps but these are
    shrunk with madvise() if there is one page free at the top of the heap.
    In some circumstances this can lead to high system overhead if a thread
    has a control flow like
    
        while (data_to_process) {
            buf = malloc(large_size);
            do_stuff();
            free(buf);
        }
    
    For a large size, the free() will call madvise (pagetable teardown, page
    free and TLB flush) every time followed immediately by a malloc (fault,
    kernel page alloc, zeroing and charge accounting). The kernel overhead
    can dominate such a workload.
    
    This patch allows the user to tune when madvise gets called by applying
    the trim threshold to the per-thread heaps and using similar logic to the
    main arena when deciding whether to shrink. Alternatively if the dynamic
    brk/mmap threshold gets adjusted then the new values will be obeyed by
    the per-thread heaps.
    
    Bug 17195 was a test case motivated by a problem encountered in scientific
    applications written in python that performance badly due to high page fault
    overhead. The basic operation of such a program was posted by Julian Taylor
    https://sourceware.org/ml/libc-alpha/2015-02/msg00373.html
    
    With this patch applied, the overhead is eliminated. All numbers in this
    report are in seconds and were recorded by running Julian's program 30
    times.
    
    pyarray
                                     glibc               madvise
                                      2.21                    v2
    System  min             1.81 (  0.00%)        0.00 (100.00%)
    System  mean            1.93 (  0.00%)        0.02 ( 99.20%)
    System  stddev          0.06 (  0.00%)        0.01 ( 88.99%)
    System  max             2.06 (  0.00%)        0.03 ( 98.54%)
    Elapsed min             3.26 (  0.00%)        2.37 ( 27.30%)
    Elapsed mean            3.39 (  0.00%)        2.41 ( 28.84%)
    Elapsed stddev          0.14 (  0.00%)        0.02 ( 82.73%)
    Elapsed max             4.05 (  0.00%)        2.47 ( 39.01%)
    
                   glibc     madvise
                    2.21          v2
    User          141.86      142.28
    System         57.94        0.60
    Elapsed       102.02       72.66
    
    Note that almost a minutes worth of system time is eliminted and the
    program completes 28% faster on average.
    
    To illustrate the problem without python this is a basic test-case for
    the worst case scenario where every free is a madvise followed by a an alloc
    
    /* gcc bench-free.c -lpthread -o bench-free */
    static int num = 1024;
    
    void __attribute__((noinline,noclone)) dostuff (void *p)
    {
    }
    
    void *worker (void *data)
    {
      int i;
    
      for (i = num; i--;)
        {
          void *m = malloc (48*4096);
          dostuff (m);
          free (m);
        }
    
      return NULL;
    }
    
    int main()
    {
      int i;
      pthread_t t;
      void *ret;
      if (pthread_create (&t, NULL, worker, NULL))
        exit (2);
      if (pthread_join (t, &ret))
        exit (3);
      return 0;
    }
    
    Before the patch, this resulted in 1024 calls to madvise. With the patch applied,
    madvise is called twice because the default trim threshold is high enough to avoid
    this.
    
    This a more complex case where there is a mix of frees. It's simply a different worker
    function for the test case above
    
    void *worker (void *data)
    {
      int i;
      int j = 0;
      void *free_index[num];
    
      for (i = num; i--;)
        {
          void *m = malloc ((i % 58) *4096);
          dostuff (m);
          if (i % 2 == 0) {
            free (m);
          } else {
            free_index[j++] = m;
          }
        }
      for (; j >= 0; j--)
        {
          free(free_index[j]);
        }
    
      return NULL;
    }
    
    glibc 2.21 calls malloc 90305 times but with the patch applied, it's
    called 13438. Increasing the trim threshold will decrease the number of
    times it's called with the option of eliminating the overhead.
    
    ebizzy is meant to generate a workload resembling common web application
    server workloads. It is threaded with a large working set that at its core
    has an allocation, do_stuff, free loop that also hits this case. The primary
    metric of the benchmark is records processed per second. This is running on
    my desktop which is a single socket machine with an I7-4770 and 8 cores.
    Each thread count was run for 30 seconds. It was only run once as the
    performance difference is so high that the variation is insignificant.
    
                    glibc 2.21              patch
    threads 1            10230              44114
    threads 2            19153              84925
    threads 4            34295             134569
    threads 8            51007             183387
    
    Note that the saving happens to be a concidence as the size allocated
    by ebizzy was less than the default threshold. If a different number of
    chunks were specified then it may also be necessary to tune the threshold
    to compensate
    
    This is roughly quadrupling the performance of this benchmark. The difference in
    system CPU usage illustrates why.
    
    ebizzy running 1 thread with glibc 2.21
    10230 records/s 306904
    real 30.00 s
    user  7.47 s
    sys  22.49 s
    
    22.49 seconds was spent in the kernel for a workload runinng 30 seconds. With the
    patch applied
    
    ebizzy running 1 thread with patch applied
    44126 records/s 1323792
    real 30.00 s
    user 29.97 s
    sys   0.00 s
    
    system CPU usage was zero with the patch applied. strace shows that glibc
    running this workload calls madvise approximately 9000 times a second. With
    the patch applied madvise was called twice during the workload (or 0.06
    times per second).
    
    2015-02-10  Mel Gorman  <mgorman@suse.de>
    
      [BZ #17195]
      * malloc/arena.c (free): Apply trim threshold to per-thread heaps
        as well as the main arena.

Index: glibc-2.17-c758a686/malloc/arena.c
===================================================================
--- glibc-2.17-c758a686.orig/malloc/arena.c
+++ glibc-2.17-c758a686/malloc/arena.c
@@ -661,7 +661,7 @@ heap_trim(heap_info *heap, size_t pad)
   unsigned long pagesz = GLRO(dl_pagesize);
   mchunkptr top_chunk = top(ar_ptr), p, bck, fwd;
   heap_info *prev_heap;
-  long new_size, top_size, extra, prev_size, misalign;
+  long new_size, top_size, top_area, extra, prev_size, misalign;
 
   /* Can this heap go away completely? */
   while(top_chunk == chunk_at_offset(heap, sizeof(*heap))) {
@@ -695,9 +695,16 @@ heap_trim(heap_info *heap, size_t pad)
     set_head(top_chunk, new_size | PREV_INUSE);
     /*check_chunk(ar_ptr, top_chunk);*/
   }
+
+  /* Uses similar logic for per-thread arenas as the main arena with systrim
+     by preserving the top pad and at least a page.  */
   top_size = chunksize(top_chunk);
-  extra = (top_size - pad - MINSIZE - 1) & ~(pagesz - 1);
-  if(extra < (long)pagesz)
+  top_area = top_size - MINSIZE - 1;
+  if (top_area <= pad)
+    return 0;
+
+  extra = ALIGN_DOWN(top_area - pad, pagesz);
+  if ((unsigned long) extra < mp_.trim_threshold)
     return 0;
   /* Try to shrink. */
   if(shrink_heap(heap, extra) != 0)
Index: glibc-2.17-c758a686/malloc/malloc.c
===================================================================
--- glibc-2.17-c758a686.orig/malloc/malloc.c
+++ glibc-2.17-c758a686/malloc/malloc.c
@@ -236,6 +236,8 @@
 /* For va_arg, va_start, va_end.  */
 #include <stdarg.h>
 
+/* For ALIGN_UP.  */
+#include <libc-internal.h>
 
 /*
   Debugging: