• Kirill A. Shutemov's avatar
    mm: account pmd page tables to the process · dc6c9a35
    Kirill A. Shutemov authored
    Dave noticed that unprivileged process can allocate significant amount of
    memory -- >500 MiB on x86_64 -- and stay unnoticed by oom-killer and
    memory cgroup.  The trick is to allocate a lot of PMD page tables.  Linux
    kernel doesn't account PMD tables to the process, only PTE.
    The use-cases below use few tricks to allocate a lot of PMD page tables
    while keeping VmRSS and VmPTE low.  oom_score for the process will be 0.
    	#include <errno.h>
    	#include <stdio.h>
    	#include <stdlib.h>
    	#include <unistd.h>
    	#include <sys/mman.h>
    	#include <sys/prctl.h>
    	#define PUD_SIZE (1UL << 30)
    	#define PMD_SIZE (1UL << 21)
    	#define NR_PUD 130000
    	int main(void)
    		char *addr = NULL;
    		unsigned long i;
    		for (i = 0; i < NR_PUD ; i++) {
    			addr = mmap(addr + PUD_SIZE, PUD_SIZE, PROT_WRITE|PROT_READ,
    			if (addr == MAP_FAILED) {
    			*addr = 'x';
    			munmap(addr, PMD_SIZE);
    			mmap(addr, PMD_SIZE, PROT_WRITE|PROT_READ,
    			if (addr == MAP_FAILED)
    				perror("re-mmap"), exit(1);
    		printf("PID %d consumed %lu KiB in PMD page tables\n",
    				getpid(), i * 4096 >> 10);
    		return pause();
    The patch addresses the issue by account PMD tables to the process the
    same way we account PTE.
    The main place where PMD tables is accounted is __pmd_alloc() and
    free_pmd_range(). But there're few corner cases:
     - HugeTLB can share PMD page tables. The patch handles by accounting
       the table to all processes who share it.
     - x86 PAE pre-allocates few PMD tables on fork.
     - Architectures with FIRST_USER_ADDRESS > 0. We need to adjust sanity
       check on exit(2).
    Accounting only happens on configuration where PMD page table's level is
    present (PMD is not folded).  As with nr_ptes we use per-mm counter.  The
    counter value is used to calculate baseline for badness score by
    Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Reported-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
    Cc: Hugh Dickins <hughd@google.com>
    Reviewed-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
    Cc: Pavel Emelyanov <xemul@openvz.org>
    Cc: David Rientjes <rientjes@google.com>
    Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
debug.c 6.5 KB