• Huang, Ying's avatar
    mm/swap: split swap cache into 64MB trunks · 4b3ef9da
    Huang, Ying authored
    The patch is to improve the scalability of the swap out/in via using
    fine grained locks for the swap cache.  In current kernel, one address
    space will be used for each swap device.  And in the common
    configuration, the number of the swap device is very small (one is
    typical).  This causes the heavy lock contention on the radix tree of
    the address space if multiple tasks swap out/in concurrently.
    But in fact, there is no dependency between pages in the swap cache.  So
    that, we can split the one shared address space for each swap device
    into several address spaces to reduce the lock contention.  In the
    patch, the shared address space is split into 64MB trunks.  64MB is
    chosen to balance the memory space usage and effect of lock contention
    The size of struct address_space on x86_64 architecture is 408B, so with
    the patch, 6528B more memory will be used for every 1GB swap space on
    x86_64 architecture.
    One address space is still shared for the swap entries in the same 64M
    trunks.  To avoid lock contention for the first round of swap space
    allocation, the order of the swap clusters in the initial free clusters
    list is changed.  The swap space distance between the consecutive swap
    clusters in the free cluster list is at least 64M.  After the first
    round of allocation, the swap clusters are expected to be freed
    randomly, so the lock contention should be reduced effectively.
    Link: http://lkml.kernel.org/r/735bab895e64c930581ffb0a05b661e01da82bc5.1484082593.git.tim.c.chen@linux.intel.com
    Signed-off-by: default avatar"Huang, Ying" <ying.huang@intel.com>
    Signed-off-by: default avatarTim Chen <tim.c.chen@linux.intel.com>
    Cc: Aaron Lu <aaron.lu@intel.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Christian Borntraeger <borntraeger@de.ibm.com>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
    Cc: Huang Ying <ying.huang@intel.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Jonathan Corbet <corbet@lwn.net> escreveu:
    Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Shaohua Li <shli@kernel.org>
    Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>