• KOSAKI Motohiro's avatar
    mm: fix Committed_AS underflow on large NR_CPUS environment · 00a62ce9
    KOSAKI Motohiro authored
    The Committed_AS field can underflow in certain situations:
    
    >         # while true; do cat /proc/meminfo  | grep _AS; sleep 1; done | uniq -c
    >               1 Committed_AS: 18446744073709323392 kB
    >              11 Committed_AS: 18446744073709455488 kB
    >               6 Committed_AS:    35136 kB
    >               5 Committed_AS: 18446744073709454400 kB
    >               7 Committed_AS:    35904 kB
    >               3 Committed_AS: 18446744073709453248 kB
    >               2 Committed_AS:    34752 kB
    >               9 Committed_AS: 18446744073709453248 kB
    >               8 Committed_AS:    34752 kB
    >               3 Committed_AS: 18446744073709320960 kB
    >               7 Committed_AS: 18446744073709454080 kB
    >               3 Committed_AS: 18446744073709320960 kB
    >               5 Committed_AS: 18446744073709454080 kB
    >               6 Committed_AS: 18446744073709320960 kB
    
    Because NR_CPUS can be greater than 1000 and meminfo_proc_show() does
    not check for underflow.
    
    But NR_CPUS proportional isn't good calculation.  In general,
    possibility of lock contention is proportional to the number of online
    cpus, not theorical maximum cpus (NR_CPUS).
    
    The current kernel has generic percpu-counter stuff.  using it is right
    way.  it makes code simplify and percpu_counter_read_positive() don't
    make underflow issue.
    Reported-by: default avatarDave Hansen <dave@linux.vnet.ibm.com>
    Signed-off-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Cc: Eric B Munson <ebmunson@us.ibm.com>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Christoph Lameter <cl@linux-foundation.org>
    Cc: <stable@kernel.org>		[All kernel versions]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    00a62ce9
mmap.c 64.3 KB