Messages in this thread |  | | | From | Tejun Heo <> | | Subject | [RFC PATCHSET tip:x86/mm] Remove DISCONTIGMEM support from x86-32 | | Date | Thu, 31 Mar 2011 20:02:42 +0200 |
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Hello,
This patchset removes DISCONTIGMEM support from x86-32 leaving it with FLATMEM for UMA and SPARSEMEM for NUMA. At this point, DISCONTIGMEM doesn't really have much benefit over SPARSEMEM. The only remaining benefit is that it can have finer granularity with memsections regardless of the number of bits available in page->flags.
There are two obstacles to removing DISCONTIGMEM support in x86-32. One is that ARCH_SUPPORTS_MEMORY_FAILURE is dependent on !SPARSEMEM, so if a NUMA kernel wants to use memory failure, it has to use DISCONTIGMEM. At least SLE11SP1 kernel seems to have chosen that route.
This is solved by reducing the number of page->flags bits used for memsection selection by one, which I think is the right thing to do regardless of this change. Please read the patch description on the second patch for details.
The other obstable is that due to the limited number of page->flags bits available and the relatively large physical address area when PAE is enabled, the granularity of sparse memsections is somewhat coarse. It was originally 512MiB but increased to 1GiB with the second patch.
For unaligned memsections, this can result in some amount of wasted struct page allocations, which I think shouldn't be a problem but not completely sure and thus the RFC status.
This patchset contains the following four patches.
0001-x86-Clean-up-memory-model-related-configs-in-arch-x8.patch 0002-x86-32-Increment-SECTION_SIZE_BITS-to-30-when-X86_PA.patch 0003-x86-32-Remove-restrictions-on-ARCH_SUPPORTS_MEMORY_F.patch 0004-x86-32-NUMA-Remove-support-for-DISCONTIGMEM.patch
0001 is a cleanup which I'll probably queue regardless of this series unless there are objections. 0002-0003 solve the first obstacle described above and 0004 removes DISCONTIGMEM.
The patchset is also available in the following git branch.
git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git x86_32-remove-DISCONTIGMEM
diffstat follows. arch/x86/Kconfig | 49 +++++++++------------------------ arch/x86/include/asm/mmzone_32.h | 48 -------------------------------- arch/x86/include/asm/pgtable_32.h | 5 --- arch/x86/include/asm/sparsemem.h | 2 - arch/x86/mm/numa_32.c | 56 ++++---------------------------------- 5 files changed, 22 insertions(+), 138 deletions(-) Thanks.
-- tejun
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