• Roman Gushchin's avatar
    mm: hugetlb: optionally allocate gigantic hugepages using cma · cf11e85f
    Roman Gushchin authored
    Commit 944d9fec ("hugetlb: add support for gigantic page allocation
    at runtime") has added the run-time allocation of gigantic pages.
    
    However it actually works only at early stages of the system loading,
    when the majority of memory is free.  After some time the memory gets
    fragmented by non-movable pages, so the chances to find a contiguous 1GB
    block are getting close to zero.  Even dropping caches manually doesn't
    help a lot.
    
    At large scale rebooting servers in order to allocate gigantic hugepages
    is quite expensive and complex.  At the same time keeping some constant
    percentage of memory in reserved hugepages even if the workload isn't
    using it is a big waste: not all workloads can benefit from using 1 GB
    pages.
    
    The following solution can solve the problem:
    1) On boot time a dedicated cma area* is reserved. The size is passed
       as a kernel argument.
    2) Run-time allocations of gigantic hugepages are performed using the
       cma allocator and the dedicated cma area
    
    In this case gigantic hugepages can be allocated successfully with a
    high probability, however the memory isn't completely wasted if nobody
    is using 1GB hugepages: it can be used for pagecache, anon memory, THPs,
    etc.
    
    * On a multi-node machine a per-node cma area is allocated on each node.
      Following gigantic hugetlb allocation are using the first available
      numa node if the mask isn't specified by a user.
    
    Usage:
    1) configure the kernel to allocate a cma area for hugetlb allocations:
       pass hugetlb_cma=10G as a kernel argument
    
    2) allocate hugetlb pages as usual, e.g.
       echo 10 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
    
    If the option isn't enabled or the allocation of the cma area failed,
    the current behavior of the system is preserved.
    
    x86 and arm-64 are covered by this patch, other architectures can be
    trivially added later.
    
    The patch contains clean-ups and fixes proposed and implemented by Aslan
    Bakirov and Randy Dunlap.  It also contains ideas and suggestions
    proposed by Rik van Riel, Michal Hocko and Mike Kravetz.  Thanks!
    Signed-off-by: default avatarRoman Gushchin <guro@fb.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Tested-by: default avatarAndreas Schaufler <andreas.schaufler@gmx.de>
    Acked-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
    Acked-by: default avatarMichal Hocko <mhocko@kernel.org>
    Cc: Aslan Bakirov <aslan@fb.com>
    Cc: Randy Dunlap <rdunlap@infradead.org>
    Cc: Rik van Riel <riel@surriel.com>
    Cc: Joonsoo Kim <js1304@gmail.com>
    Link: http://lkml.kernel.org/r/20200407163840.92263-3-guro@fb.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    cf11e85f
hugetlb.c 153 KB