nommu: make the initial mmap allocation excess behaviour Kconfig configurable

[pandora-kernel.git] / mm / Kconfig

diff --git a/mm/Kconfig b/mm/Kconfig
index 57971d2..c2b57d8 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -225,3 +225,31 @@ config HAVE_MLOCKED_PAGE_BIT
 
 config MMU_NOTIFIER
        bool
+
+config NOMMU_INITIAL_TRIM_EXCESS
+       int "Turn on mmap() excess space trimming before booting"
+       depends on !MMU
+       default 1
+       help
+         The NOMMU mmap() frequently needs to allocate large contiguous chunks
+         of memory on which to store mappings, but it can only ask the system
+         allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
+         more than it requires.  To deal with this, mmap() is able to trim off
+         the excess and return it to the allocator.
+
+         If trimming is enabled, the excess is trimmed off and returned to the
+         system allocator, which can cause extra fragmentation, particularly
+         if there are a lot of transient processes.
+
+         If trimming is disabled, the excess is kept, but not used, which for
+         long-term mappings means that the space is wasted.
+
+         Trimming can be dynamically controlled through a sysctl option
+         (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
+         excess pages there must be before trimming should occur, or zero if
+         no trimming is to occur.
+
+         This option specifies the initial value of this option.  The default
+         of 1 says that all excess pages should be trimmed.
+
+         See Documentation/nommu-mmap.txt for more information.