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  1. MariaDB Server
  2. MDEV-40921

Large allocations Use MMAP_NORESERVE (but not large_pages)

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    • Can result in unexpected behaviour
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      Large memory allocations use MAP_NORESERVE where available (Linux and Illumos) to ensure that large memory mappings (e.g. 8TiB on default innodb_buffer_pool_size_max) do not result in memory actually being reserved (which it is by default on Illumos). --large-page memory behaviour isn't changed.
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      Large memory allocations use MAP_NORESERVE where available (Linux and Illumos) to ensure that large memory mappings (e.g. 8TiB on default innodb_buffer_pool_size_max) do not result in memory actually being reserved (which it is by default on Illumos). --large-page memory behaviour isn't changed.

    Description

      From fiddaman - https://jira.mariadb.org/browse/MDEV-38671?focusedCommentId=336602&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-336602

      Having just upgraded mariadb on a system running illumos, this change has bitten me:

      2026-08-04 12:21:11 0 [ERROR] InnoDB: Cannot map innodb_buffer_pool_size_max=8388608m
      		 
       2026-08-04 12:21:11 0 [ERROR] InnoDB: Plugin initialization aborted with error Generic error

      On Linux a `PROT_NONE` anonymous mapping costs nothing, but on illumos any anonymous mapping without `MAP_NORESERVE` reserves swap at map time regardless of protection (https://man.omnios.org/man4/swap).
      I fixed it by explicitly adding smaller limits to `my.cnf` for am also planning to apply the following patch:

      --- a~/mysys/my_largepage.c     1970-01-01 00:00:00
      		 
      +++ a/mysys/my_largepage.c      1970-01-01 00:00:00
      		 
      @@ -492,7 +492,11 @@ char *my_large_virtual_alloc(size_t *size)
      		 
         ptr= mmap(NULL, *size, PROT_READ | PROT_WRITE,
      		 
                   MAP_PRIVATE | OS_MAP_ANON, -1, 0);
      		 
       # else
      		 
      -  ptr= mmap(NULL, *size, PROT_NONE, MAP_PRIVATE | OS_MAP_ANON, -1, 0);
      		 
      +  ptr= mmap(NULL, *size, PROT_NONE, MAP_PRIVATE | OS_MAP_ANON
      		 
      +#  ifdef __illumos__
      		 
      +            | MAP_NORESERVE
      		 
      +#  endif /* __illumos__ */
      		 
      +            , -1, 0);
      		 
       # endif
      		 
         if (ptr == MAP_FAILED)
      		 
           ptr= NULL;

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          relates to

          Bug - A problem which impairs or prevents the functions of the product. MDEV-38671 SET GLOBAL innodb_buffer_pool_size cannot be increased by default

          • Blocker - Blocks development and/or testing work, production could not run.
          • Closed
          links to

          Web Link Linux docs - MAP_NORESERVE implications - overcommit modes

          Web Link omnios distro patch

          Web Link omnios man 2 - mmap

          Web Link omnios man 4 - swap - illumos reserved by default

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              danblack Daniel Black
              danblack Daniel Black
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