21 Jan, 2015

1 commit

  • Since "BDI: Provide backing device capability information [try #3]" the
    backing_dev_info structure also provides flags for the kind of mmap
    operation available in a nommu environment, which is entirely unrelated
    to it's original purpose.

    Introduce a new nommu-only file operation to provide this information to
    the nommu mmap code instead. Splitting this from the backing_dev_info
    structure allows to remove lots of backing_dev_info instance that aren't
    otherwise needed, and entirely gets rid of the concept of providing a
    backing_dev_info for a character device. It also removes the need for
    the mtd_inodefs filesystem.

    Signed-off-by: Christoph Hellwig
    Reviewed-by: Tejun Heo
    Acked-by: Brian Norris
    Signed-off-by: Jens Axboe

    Christoph Hellwig
     

16 Dec, 2009

1 commit

  • The NOMMU code currently clears all anonymous mmapped memory. While this
    is what we want in the default case, all memory allocation from userspace
    under NOMMU has to go through this interface, including malloc() which is
    allowed to return uninitialized memory. This can easily be a significant
    performance penalty. So for constrained embedded systems were security is
    irrelevant, allow people to avoid clearing memory unnecessarily.

    This also alters the ELF-FDPIC binfmt such that it obtains uninitialised
    memory for the brk and stack region.

    Signed-off-by: Jie Zhang
    Signed-off-by: Robin Getz
    Signed-off-by: Mike Frysinger
    Signed-off-by: David Howells
    Acked-by: Paul Mundt
    Acked-by: Greg Ungerer
    Signed-off-by: Andrew Morton
    Signed-off-by: Linus Torvalds

    Jie Zhang
     

08 Jan, 2009

2 commits

  • NOMMU mmap allocates a piece of memory for an mmap that's rounded up in size to
    the nearest power-of-2 number of pages. Currently it then discards the excess
    pages back to the page allocator, making that memory available for use by other
    things. This can, however, cause greater amount of fragmentation.

    To counter this, a sysctl is added in order to fine-tune the trimming
    behaviour. The default behaviour remains to trim pages aggressively, while
    this can either be disabled completely or set to a higher page-granular
    watermark in order to have finer-grained control.

    vm region vm_top bits taken from an earlier patch by David Howells.

    Signed-off-by: Paul Mundt
    Signed-off-by: David Howells
    Tested-by: Mike Frysinger

    Paul Mundt
     
  • Make VMAs per mm_struct as for MMU-mode linux. This solves two problems:

    (1) In SYSV SHM where nattch for a segment does not reflect the number of
    shmat's (and forks) done.

    (2) In mmap() where the VMA's vm_mm is set to point to the parent mm by an
    exec'ing process when VM_EXECUTABLE is specified, regardless of the fact
    that a VMA might be shared and already have its vm_mm assigned to another
    process or a dead process.

    A new struct (vm_region) is introduced to track a mapped region and to remember
    the circumstances under which it may be shared and the vm_list_struct structure
    is discarded as it's no longer required.

    This patch makes the following additional changes:

    (1) Regions are now allocated with alloc_pages() rather than kmalloc() and
    with no recourse to __GFP_COMP, so the pages are not composite. Instead,
    each page has a reference on it held by the region. Anything else that is
    interested in such a page will have to get a reference on it to retain it.
    When the pages are released due to unmapping, each page is passed to
    put_page() and will be freed when the page usage count reaches zero.

    (2) Excess pages are trimmed after an allocation as the allocation must be
    made as a power-of-2 quantity of pages.

    (3) VMAs are added to the parent MM's R/B tree and mmap lists. As an MM may
    end up with overlapping VMAs within the tree, the VMA struct address is
    appended to the sort key.

    (4) Non-anonymous VMAs are now added to the backing inode's prio list.

    (5) Holes may be punched in anonymous VMAs with munmap(), releasing parts of
    the backing region. The VMA and region structs will be split if
    necessary.

    (6) sys_shmdt() only releases one attachment to a SYSV IPC shared memory
    segment instead of all the attachments at that addresss. Multiple
    shmat()'s return the same address under NOMMU-mode instead of different
    virtual addresses as under MMU-mode.

    (7) Core dumping for ELF-FDPIC requires fewer exceptions for NOMMU-mode.

    (8) /proc/maps is now the global list of mapped regions, and may list bits
    that aren't actually mapped anywhere.

    (9) /proc/meminfo gains a line (tagged "MmapCopy") that indicates the amount
    of RAM currently allocated by mmap to hold mappable regions that can't be
    mapped directly. These are copies of the backing device or file if not
    anonymous.

    These changes make NOMMU mode more similar to MMU mode. The downside is that
    NOMMU mode requires some extra memory to track things over NOMMU without this
    patch (VMAs are no longer shared, and there are now region structs).

    Signed-off-by: David Howells
    Tested-by: Mike Frysinger
    Acked-by: Paul Mundt

    David Howells
     

27 Sep, 2006

4 commits

  • Make futexes work under NOMMU conditions.

    This can be tested by running this in one shell:

    #define SYSERROR(X, Y) \
    do { if ((long)(X) == -1L) { perror(Y); exit(1); }} while(0)

    int main()
    {
    int shmid, tmp, *f, n;

    shmid = shmget(23, 4, IPC_CREAT|0666);
    SYSERROR(shmid, "shmget");

    f = shmat(shmid, NULL, 0);
    SYSERROR(f, "shmat");

    n = *f;
    printf("WAIT: %p{%x}\n", f, n);
    tmp = futex(f, FUTEX_WAIT, n, NULL, NULL, 0);
    SYSERROR(tmp, "futex");
    printf("WAITED: %d\n", tmp);

    tmp = shmdt(f);
    SYSERROR(tmp, "shmdt");

    exit(0);
    }

    And then this in the other shell:

    #define SYSERROR(X, Y) \
    do { if ((long)(X) == -1L) { perror(Y); exit(1); }} while(0)

    int main()
    {
    int shmid, tmp, *f;

    shmid = shmget(23, 4, IPC_CREAT|0666);
    SYSERROR(shmid, "shmget");

    f = shmat(shmid, NULL, 0);
    SYSERROR(f, "shmat");

    (*f)++;
    printf("WAKE: %p{%x}\n", f, *f);
    tmp = futex(f, FUTEX_WAKE, 1, NULL, NULL, 0);
    SYSERROR(tmp, "futex");
    printf("WOKE: %d\n", tmp);

    tmp = shmdt(f);
    SYSERROR(tmp, "shmdt");

    exit(0);
    }

    The first program will set up a SYSV IPC SHM segment and wait on a futex in it
    for the number at the start to change. The program will increment that number
    and wake the first program up. This leads to output of the form:

    SHELL 1 SHELL 2
    ======================= =======================
    # /dowait
    WAIT: 0xc32ac000{0}
    # /dowake
    WAKE: 0xc32ac000{1}
    WAITED: 0 WOKE: 1

    Signed-off-by: David Howells
    Signed-off-by: Andrew Morton
    Signed-off-by: Linus Torvalds

    David Howells
     
  • Add documentation about using shared memory in NOMMU mode.

    Signed-off-by: David Howells
    Signed-off-by: Andrew Morton
    Signed-off-by: Linus Torvalds

    David Howells
     
  • Make mremap() partially work for NOMMU kernels. It may resize a VMA provided
    that it doesn't exceed the size of the slab object in which the storage is
    allocated that the VMA refers to. Shareable VMAs may not be resized.

    Moving VMAs (as permitted by MREMAP_MAYMOVE) is not currently supported.

    This patch also makes use of the fact that the VMA list is now ordered to cut
    it short when possible.

    Signed-off-by: David Howells
    Signed-off-by: Andrew Morton
    Signed-off-by: Linus Torvalds

    David Howells
     
  • Implement /proc/pid/maps for NOMMU by reading the vm_area_list attached to
    current->mm->context.vmlist.

    Signed-off-by: David Howells
    Signed-off-by: Andrew Morton
    Signed-off-by: Linus Torvalds

    David Howells
     

17 Apr, 2005

1 commit

  • Initial git repository build. I'm not bothering with the full history,
    even though we have it. We can create a separate "historical" git
    archive of that later if we want to, and in the meantime it's about
    3.2GB when imported into git - space that would just make the early
    git days unnecessarily complicated, when we don't have a lot of good
    infrastructure for it.

    Let it rip!

    Linus Torvalds