[Bugme-new] [Bug 13618] New: MAP_NOSYNC for mmap()

[bugzilla-daemon at bugzilla.kernel.org]

http://bugzilla.kernel.org/show_bug.cgi?id=13618

           Summary: MAP_NOSYNC for mmap()
           Product: Memory Management
           Version: 2.5
    Kernel Version: any
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Other
        AssignedTo: akpm at linux-foundation.org
        ReportedBy: ninive at gmx.at
        Regression: No


Hello,

This is not a bug, but a feature/enhancement request.

Many databases (e.g. BDB) use "mmap()" to create a
memory cache.
The problem: the modified cache is constantly written
to mmaped-file on the harddisk.

On *BSD you simply use the flag MAP_NOSYNC for "mmap()".
The *BSD manpage:
NOSYNC: Causes data dirtied via this VM map to be flushed to
physical media only when necessary (usually by the pager)
rather then gratuitously.  Typically this prevents the update
daemons from flushing pages dirtied through such maps and thus
allows efficient sharing of memory across unassociated processes
using a file-backed shared memory map.

Maybe this would be also a great idea for linux?

Thanks
Marcus

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