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* [Bug 1898011] [NEW] mmap MAP_NORESERVE of 2^42 bytes consumes 16Gb of actual RAM
@ 2020-10-01  6:30 Kostya Serebryany
  2020-10-02 22:34 ` [Bug 1898011] " Richard Henderson
                   ` (5 more replies)
  0 siblings, 6 replies; 7+ messages in thread
From: Kostya Serebryany @ 2020-10-01  6:30 UTC (permalink / raw)
  To: qemu-devel

Public bug reported:

Run this program:

#include <sys/mman.h>
#include <stdio.h>
int main() {
        for (int i = 30; i <= 44; i++) {
                fprintf(stderr, "trying 2**%d\n", i);
                mmap((void*)0x600000000000,1ULL << i,
                        PROT_NONE,
                        MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_NORESERVE,-1,0);
        }
}

(tried qemu-x86_64 and qemu-aarch64, 4.2.1 and trunk/5.1.50)

On each iteration qemu will consume 2x more physical RAM, 
e.g. when mapping 2^42 it will have RSS of 16Gb.

On normal linux it works w/o consuming much RAM, due to MAP_NORESERVE.

Also: qemu -strace prints 0 instead of the correct size starting from size=2^32
and prints -2147483648 for size=2^31. 

mmap(0x0000600000000000,1073741824,PROT_NONE,MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_NORESERVE,-1,0)
= 0x0000600000000000

mmap(0x0000600000000000,-2147483648,PROT_NONE,MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_NORESERVE,-1,0)
= 0x0000600000000000

mmap(0x0000600000000000,0,PROT_NONE,MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_NORESERVE,-1,0)
= 0x0000600000000000

** Affects: qemu
     Importance: Undecided
         Status: New

-- 
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https://bugs.launchpad.net/bugs/1898011

Title:
  mmap MAP_NORESERVE of 2^42 bytes consumes 16Gb of actual RAM

Status in QEMU:
  New

Bug description:
  Run this program:

  #include <sys/mman.h>
  #include <stdio.h>
  int main() {
          for (int i = 30; i <= 44; i++) {
                  fprintf(stderr, "trying 2**%d\n", i);
                  mmap((void*)0x600000000000,1ULL << i,
                          PROT_NONE,
                          MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_NORESERVE,-1,0);
          }
  }

  (tried qemu-x86_64 and qemu-aarch64, 4.2.1 and trunk/5.1.50)

  On each iteration qemu will consume 2x more physical RAM, 
  e.g. when mapping 2^42 it will have RSS of 16Gb.

  On normal linux it works w/o consuming much RAM, due to MAP_NORESERVE.

  Also: qemu -strace prints 0 instead of the correct size starting from size=2^32
  and prints -2147483648 for size=2^31. 

  mmap(0x0000600000000000,1073741824,PROT_NONE,MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_NORESERVE,-1,0)
  = 0x0000600000000000

  mmap(0x0000600000000000,-2147483648,PROT_NONE,MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_NORESERVE,-1,0)
  = 0x0000600000000000

  mmap(0x0000600000000000,0,PROT_NONE,MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_NORESERVE,-1,0)
  = 0x0000600000000000

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^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2021-05-14 10:13 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-10-01  6:30 [Bug 1898011] [NEW] mmap MAP_NORESERVE of 2^42 bytes consumes 16Gb of actual RAM Kostya Serebryany
2020-10-02 22:34 ` [Bug 1898011] " Richard Henderson
2021-01-28  9:49 ` Stefan Weil
2021-01-28  9:59 ` Alex Bennée
2021-05-13 12:10 ` Thomas Huth
2021-05-13 12:49 ` Richard Henderson
2021-05-14 10:05 ` Thomas Huth

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