Re: [GIT] NOMMU mmap changes
From: Mike Frysinger
Date: Tue Dec 30 2008 - 03:48:11 EST
On Tue, Dec 30, 2008 at 03:42, Andrew Morton wrote:
> On Mon, 29 Dec 2008 17:42:06 +0000 David Howells wrote:
>> Can you pull the attached request please? It makes the following changes:
>>
>> (1) Discard the askedalloc and realalloc variables from NOMMU mmap as nothing
>> uses the values computed.
>>
>> (2) Stop ELF-FDPIC and FLAT binary formats from using kobjsize() by stopping
>> them from attempting to expand the stack segments to use the full amount
>> allocated (we'd like to get rid of kobjsize()).
>>
>> (3) Support XIP on initramfs. This is simply a matter of using truncate() to
>> pre-size the files ramfs files so generated so that they are constructed
>> from contiguous pages, and so can be mapped in place with NOMMU mmap().
>>
>> (4) Make NOMMU VMAs per-MM as for MMU-mode Linux. Whilst this uses more
>> memory, it also fixes a couple of bugs:
>>
>> (*) The SYSV SHM nattch count for a segment must reflect the number of
>> attachments made, but since attachments were being shared, it did
>> not.
>>
>> (*) The VMA's vm_mm is set to point to the parent mm by an exec'ing
>> process when VM_EXECUTABLE is specified, but vm_mm was being shared
>> by all the processes that shared that VMA.
>>
>> (5) NOMMU private non-shared mmaps are allocated with alloc_pages() rather
>> than kmalloc(), and without using __GFP_COMP. This makes handling of
>> the pages in an mmap() region simpler. Excess space can be trimmed after
>> allocation (configurable in /proc/sys).
>>
>> (6) A new struct (vm_region) is introduced to track mapped regions in NOMMU
>> mode, and to handle the sharing of backing stores. This required the
>> vm_region structs of PowerPC and ARM to be renamed (the former patch has
>> been pulled via the ppc tree).
>>
>> (7) NOMMU VMAs are attached to their parent inodes as for MMU VMAs.
>>
>> (8) munmap() may do a partial unmapping.
>>
>> (9) Core dumping for ELF-FDPIC is simplified as the NOMMU- and MMU-mode code
>> behaves more similarly.
>>
>> (10) /proc/maps provided in NOMMU mode now shows the regions allocated rather
>> than the common VMA list. /proc/meminfo now shows the amount of RAM
>> currently allocated to private copies by private mmaps.
>>
>> These patches have had some soak time in linux-next. I've also applied them
>> as-are to the latest merge window and tested that on my FRV board.
>>
>> David
>> ---
>> The following changes since commit 1bda71282ded6a2e09a2db7c8884542fb46bfd4f:
>> Linus Torvalds (1):
>> Merge branch 'for-linus' of git://git.kernel.org/.../ieee1394/linux1394-2.6
>>
>> are available in the git repository at:
>>
>> git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-2.6-nommu.git master
>>
>> David Howells (8):
>> NOMMU: Rename PowerPC's struct vm_region
>> NOMMU: Rename ARM's struct vm_region
>> NOMMU: Delete askedalloc and realalloc variables
>> NOMMU: Make VMAs per MM as for MMU-mode linux
>> NOMMU: Improve procfs output using per-MM VMAs
>> FDPIC: Don't attempt to expand the userspace stack to fill the space allocated
>> FLAT: Don't attempt to expand the userspace stack to fill the space allocated
>> NOMMU: Support XIP on initramfs
>>
>> Matt Mackall (1):
>> shmem: remove unused shmem_get_unmapped_area
>>
>> Paul Mundt (2):
>> NOMMU: Make mmap allocation page trimming behaviour configurable.
>> NOMMU: Teach kobjsize() about VMA regions.
>
> hm, has this all been suitably reviewed/publicised?
it has been among the people who actually use nommu (frv/sh/blackfin).
i think we've been ragging on David for not getting this stuff in two
releases ago ;).
-mike
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