On 05.11.2007 [18:28:21 -0600], Andrew Hastings wrote:
> Allow hugetlbfs_morecore to shrink the heap.
Thanks, much easier to follow now.
> Signed-off-by: Andrew Hastings <[EMAIL PROTECTED]> on behalf of Cray Inc.
> ---
> I've run the test suite with this on x86_64 and PPC64.
>
> morecore.c | 63
> ++++++++++++++++++++++++++++++++++++++---------------
> tests/Makefile | 2 -
> tests/heapshrink.c | 48 ++++++++++++++++++++++++++++++++++++++++
> tests/run_tests.sh | 2 +
> 4 files changed, 97 insertions(+), 18 deletions(-)
>
> diff -ruNp libhugetlbfs-1.2-rename-newsize/morecore.c
> libhugetlbfs-1.2-shrink/morecore.c
> --- libhugetlbfs-1.2-rename-newsize/morecore.c 2007-11-05
> 18:20:06.831195000 -0600
> +++ libhugetlbfs-1.2-shrink/morecore.c 2007-11-02 17:32:04.000000000
> -0500
> @@ -70,7 +70,7 @@ static void *hugetlbfs_morecore(ptrdiff_
> {
> int ret;
> void *p;
> - long delta = 0;
> + long delta;
>
> DEBUG("hugetlbfs_morecore(%ld) = ...\n", (long)increment);
>
> @@ -83,13 +83,11 @@ static void *hugetlbfs_morecore(ptrdiff_
> DEBUG("heapbase = %p, heaptop = %p, mapsize = %lx, delta=%ld\n",
> heapbase, heaptop, mapsize, delta);
>
> - /* growing the heap */
> + /* align to multiple of hugepagesize. */
> + delta = ALIGN(delta, blocksize);
> +
> if (delta > 0) {
> - /*
> - * convert our request to a multiple of hugepages
> - * we will have more space allocated then used, basically
> - */
> - delta = ALIGN(delta, blocksize);
> + /* growing the heap */
>
> DEBUG("Attempting to map %ld bytes\n", delta);
>
> @@ -134,6 +132,46 @@ static void *hugetlbfs_morecore(ptrdiff_
>
> /* we now have mmap'd further */
> mapsize += delta;
> + } else if (delta < 0) {
> + /* shrinking the heap */
> +
> + if (!mapsize) {
> + WARNING("Can't shrink empty heap!");
> + return NULL;
> + }
> +
> + /*
> + * If we are forced to change the heapaddr from the
> + * original brk() value we have violated brk semantics
> + * (which we are not supposed to do). This shouldn't
> + * pose a problem until glibc tries to trim the heap to an
> + * address lower than what we aligned heapaddr to. At that
> + * point the alignment "gap" causes heap corruption.
> + * So we don't allow the heap to shrink below heapbase.
> + */
> + if (mapsize + delta < 0) {
Since this delta is known to be negative, this is really asking
if (mapsize < abs(delta))
right? That is, we can't unmap more than we have mapped. Just trying to
make sure I follow.
> + WARNING("Unable to shrink heap below %p\n", heapbase);
> + delta = -mapsize;
So we just unmap what we can instead.
> + increment = heapbase - heaptop;
a.k.a. the whole heap.
> + }
> + DEBUG("Attempting to unmap %ld bytes @ %p\n", -delta,
> + heapbase + mapsize + delta);
> + ret = munmap(heapbase + mapsize + delta, -delta);
> + if (ret) {
> + WARNING("Unmapping failed in hugetlbfs_morecore()\n");
Maybe a strerror(errno) in there, so we might be able to see why?
> + } else {
> +
> + /*
> + * Now shrink the hugetlbfs file.
> + */
> + mapsize += delta;
> + ret = ftruncate(heap_fd, mapsize);
> + if (ret) {
> + WARNING("Couldn't toss pages in "
> + "hugetlbfs_morecore()\n");
I would just say "Couldn't truncate hugetlbfs file in
hugetlbfs_morecore()". Maybe a strerror(errno) here too.
> diff -ruNp libhugetlbfs-1.2-rename-newsize/tests/heapshrink.c
> libhugetlbfs-1.2-shrink/tests/heapshrink.c
> --- libhugetlbfs-1.2-rename-newsize/tests/heapshrink.c 1969-12-31
> 18:00:00.000000000 -0600
> +++ libhugetlbfs-1.2-shrink/tests/heapshrink.c 2007-11-02
> 14:56:11.000000000 -0500
Testcase seems sane.
Does the HOWTO need updating at all?
Thanks,
Nish
--
Nishanth Aravamudan <[EMAIL PROTECTED]>
IBM Linux Technology Center
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