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GNU C Library master sources branch hjl/ld.so/master created. glibc-2.23-151-gd56ca4f


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The branch, hjl/ld.so/master has been created
        at  d56ca4f3269e47cba3e8d22ba8e48cd20d470757 (commit)

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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=d56ca4f3269e47cba3e8d22ba8e48cd20d470757

commit d56ca4f3269e47cba3e8d22ba8e48cd20d470757
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Sat Apr 2 08:25:31 2016 -0700

    Reduce number of mmap calls from __libc_memalign in ld.so
    
    __libc_memalign in ld.so allocates one page at a time and tries to
    optimize consecutive __libc_memalign calls by hoping that the next
    mmap is after the current memory allocation.
    
    However, the kernel hands out mmap addresses in top-down order, so
    this optimization in practice never happens, with the result that we
    have more mmap calls and waste a bunch of space for each __libc_memalign.
    
    This change makes __libc_memalign to mmap one page extra.  Worst case,
    the kernel never puts a backing page behind it, but best case it allows
    __libc_memalign to operate much much better.  For elf/tst-align --direct,
    it reduces number of mmap calls from 12 to 9.
    
    	* elf/dl-minimal.c (__libc_memalign): Mmap one extra page.

diff --git a/elf/dl-minimal.c b/elf/dl-minimal.c
index 762e65b..8bffdc7 100644
--- a/elf/dl-minimal.c
+++ b/elf/dl-minimal.c
@@ -66,7 +66,8 @@ __libc_memalign (size_t align, size_t n)
 
   if (alloc_ptr + n >= alloc_end || n >= -(uintptr_t) alloc_ptr)
     {
-      /* Insufficient space left; allocate another page.  */
+      /* Insufficient space left; allocate another page plus one extra
+	 page to reduce number of mmap calls.  */
       caddr_t page;
       size_t nup = (n + GLRO(dl_pagesize) - 1) & ~(GLRO(dl_pagesize) - 1);
       if (__glibc_unlikely (nup == 0))
@@ -75,6 +76,8 @@ __libc_memalign (size_t align, size_t n)
 	    return NULL;
 	  nup = GLRO(dl_pagesize);
 	}
+      else
+	nup += GLRO(dl_pagesize);
       page = __mmap (0, nup, PROT_READ|PROT_WRITE,
 		     MAP_ANON|MAP_PRIVATE, -1, 0);
       if (page == MAP_FAILED)

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