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authorDavid Howells <dhowells@redhat.com>2009-05-06 16:03:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-05-06 16:36:10 -0700
commitfc4d5c292b68ef02514d2072dcbf82d090c34875 (patch)
tree6baf6c7a472e57e99e1b6555c277060f7065f482 /init
parent3a6be87fd1e5cdbbc3b6a14d02a3efa9ecba1d3f (diff)
downloadlinux-2.6.38-lt-ux500-fc4d5c292b68ef02514d2072dcbf82d090c34875.tar.gz
nommu: make the initial mmap allocation excess behaviour Kconfig configurable
NOMMU mmap() has an option controlled by a sysctl variable that determines whether the allocations made by do_mmap_private() should have the excess space trimmed off and returned to the allocator. Make the initial setting of this variable a Kconfig configuration option. The reason there can be excess space is that the allocator only allocates in power-of-2 size chunks, but mmap()'s can be made in sizes that aren't a power of 2. There are two alternatives: (1) Keep the excess as dead space. The dead space then remains unused for the lifetime of the mapping. Mappings of shared objects such as libc, ld.so or busybox's text segment may retain their dead space forever. (2) Return the excess to the allocator. This means that the dead space is limited to less than a page per mapping, but it means that for a transient process, there's more chance of fragmentation as the excess space may be reused fairly quickly. During the boot process, a lot of transient processes are created, and this can cause a lot of fragmentation as the pagecache and various slabs grow greatly during this time. By turning off the trimming of excess space during boot and disabling batching of frees, Coldfire can manage to boot. A better way of doing things might be to have /sbin/init turn this option off. By that point libc, ld.so and init - which are all long-duration processes - have all been loaded and trimmed. Reported-by: Lanttor Guo <lanttor.guo@freescale.com> Signed-off-by: David Howells <dhowells@redhat.com> Tested-by: Lanttor Guo <lanttor.guo@freescale.com> Cc: Greg Ungerer <gerg@snapgear.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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