linux-kernel - Re: [GIT] NOMMU mmap changes

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Date:	Tue, 30 Dec 2008 03:47:53 -0500
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"David Howells" <dhowells@...hat.com>,
	torvalds@...ux-foundation.org, rgetz@...ckfin.uclinux.org,
	lethal@...ux-sh.org, bernds_cb1@...nline.de,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT] NOMMU mmap changes

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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