Long quote; please see below:
Eric B Munson wrote:
> Transparent huge pages (THP) give another option for access to huge pages for
> anonymous mappings. This patch adds the ability to specify that the process
> heap should be aligned and (if requested madvised) to be merged into huge
> pages
> by khugepaged. For more information on THP see
> linux-2.6/Documentation/transhuge.txt.
>
> Signed-off-by: Eric B Munson <[email protected]>
> ---
> HOWTO | 7 +++-
> hugeutils.c | 9 +++++
> libhugetlbfs_internal.h | 1 +
> morecore.c | 84 ++++++++++++++++++++++++++++++++++++++++++++--
> 4 files changed, 96 insertions(+), 5 deletions(-)
>
> diff --git a/HOWTO b/HOWTO
> index 3c1f124..b0727a7 100644
> --- a/HOWTO
> +++ b/HOWTO
> @@ -2,7 +2,7 @@ libhugetlbfs HOWTO
> ==================
>
> Author: David Gibson <[email protected]>, Adam Litke <[email protected]>, and
> others
> -Last updated: February 1st, 2011
> +Last updated: July 11, 2011
>
> Introduction
> ============
> @@ -264,6 +264,11 @@ environment variables:
> To use a specific huge page size:
> HUGETLB_MORECORE=<pagesize>
>
> + To use Transparent Huge Pages (THP):
> + HUGETLB_MORECORE=thp
> +
> +Note: This option requires a kernel that supports Transparent Huge Pages
> +
> Usually it's preferable to set these environment variables on the
> command line of the program you wish to run, rather than using
> "export", because you'll only want to enable the hugepage malloc() for
> diff --git a/hugeutils.c b/hugeutils.c
> index b28bd0a..a7ccda0 100644
> --- a/hugeutils.c
> +++ b/hugeutils.c
> @@ -335,6 +335,15 @@ void hugetlbfs_setup_env()
> __hugetlb_opts.morecore = getenv("HUGETLB_MORECORE");
> __hugetlb_opts.heapbase = getenv("HUGETLB_MORECORE_HEAPBASE");
>
> + if (__hugetlb_opts.morecore)
> + __hugetlb_opts.thp_morecore =
> + (strcasecmp(__hugetlb_opts.morecore, "thp") == 0);
> +
> + if (__hugetlb_opts.thp_morecore && __hugetlb_opts.heapbase) {
> + DEBUG("Heapbase specified with THP for morecore, ignoring
> heapbase\n");
> + __hugetlb_opts.heapbase = NULL;
> + }
> +
> env = getenv("HUGETLB_FORCE_ELFMAP");
> if (env && (strcasecmp(env, "yes") == 0))
> __hugetlb_opts.force_elfmap = 1;
> diff --git a/libhugetlbfs_internal.h b/libhugetlbfs_internal.h
> index 97b19fa..ae8d7bc 100644
> --- a/libhugetlbfs_internal.h
> +++ b/libhugetlbfs_internal.h
> @@ -63,6 +63,7 @@ struct libhugeopts_t {
> bool shm_enabled;
> bool no_reserve;
> bool map_hugetlb;
> + bool thp_morecore;
> unsigned long force_elfmap;
> char *ld_preload;
> char *elfmap;
> diff --git a/morecore.c b/morecore.c
> index 6b4364c..c2a445c 100644
> --- a/morecore.c
> +++ b/morecore.c
> @@ -202,6 +202,72 @@ static void *hugetlbfs_morecore(ptrdiff_t increment)
> return p;
> }
>
> +static void *thp_morecore(ptrdiff_t increment)
> +{
> + void *p;
> + long delta;
> +
> + INFO("thp_morecore(%ld) = ...\n", (long)increment);
> +
> + delta = (heaptop - heapbase) + increment - mapsize;
> + delta = ALIGN(delta, hpage_size);
> +
> + if (delta > 0) {
> + /*
> + * This first time we expand the mapping we need to account for
> + * the initial heap mapping not necessarily being huge page
> + * aligned
> + */
> + if (!mapsize)
> + delta = hugetlbfs_next_addr((long)heapbase + delta) -
> + (unsigned long)heapbase;
> +
> + INFO("Adding %ld bytes to heap\n", delta);
> +
> + p = sbrk(delta);
> + if (p == (void *)-1) {
> + WARNING("sbrk returned ENOMEM\n");
> + return NULL;
> + }
> +
> + if (!mapsize) {
> + if (heapbase && (heapbase != p)) {
> + WARNING("Heap originates at %p instead of %p\n",
> + p, heapbase);
> + if (__hugetlbfs_debug)
> + dump_proc_pid_maps();
It took me a while to figure out how this 'if' might be true. I believe it
means that the sbrk value changed between hugetlbfs_setup_morecore and here.
Might it be worthwhile to change the warning text to make this clearer? It's
quite different from setting the HUGETLB_MORECORE_BASE env. var.
> + }
> + heapbase = heaptop = p;
> + }
> +
> + mapsize += delta;
> +#ifdef MADV_HUGEPAGE
> + madvise(p, delta, MADV_HUGEPAGE);
> +#endif
> + } else if (delta < 0) {
> + /* shrinking the heap */
> + if (!mapsize) {
> + WARNING("Can't shrink an empty heap\n");
> + return NULL;
> + }
> +
> + INFO("Attempting to shrink heap by %ld bytes with sbrk\n",
> + -delta);
> + p = sbrk(delta);
> + if (p == (void *)-1) {
> + WARNING("Unable to shrink heap\n");
> + return heaptop;
> + }
> +
> + mapsize += delta;
> + }
> +
> + p = heaptop;
> + heaptop += increment;
> + INFO("... = %p\n", p);
> + return p;
> +}
> +
> void hugetlbfs_setup_morecore(void)
> {
> char *ep;
> @@ -222,6 +288,8 @@ void hugetlbfs_setup_morecore(void)
> */
> if (strncasecmp(__hugetlb_opts.morecore, "y", 1) == 0)
> hpage_size = gethugepagesize();
> + else if (__hugetlb_opts.thp_morecore)
> + hpage_size = kernel_default_hugepage_size();
> else
> hpage_size = parse_page_size(__hugetlb_opts.morecore);
>
> @@ -237,8 +305,12 @@ void hugetlbfs_setup_morecore(void)
> return;
> }
>
> - if(__hugetlb_opts.map_hugetlb &&
> - hpage_size == kernel_default_hugepage_size()) {
> + /*
> + * We won't need an fd for the heap mmaps if we are using MAP_HUGETLB
> + * or we are depending on transparent huge pages
> + */
> + if(__hugetlb_opts.thp_morecore || (__hugetlb_opts.map_hugetlb &&
> + hpage_size == kernel_default_hugepage_size())) {
> heap_fd = -1;
> } else {
> if (!hugetlbfs_find_path_for_size(hpage_size)) {
> @@ -262,13 +334,17 @@ void hugetlbfs_setup_morecore(void)
> }
> } else {
> heapaddr = (unsigned long)sbrk(0);
> - heapaddr = hugetlbfs_next_addr(heapaddr);
> + if (!__hugetlb_opts.thp_morecore)
> + heapaddr = hugetlbfs_next_addr(heapaddr);
> }
>
> INFO("setup_morecore(): heapaddr = 0x%lx\n", heapaddr);
>
> heaptop = heapbase = (void *)heapaddr;
> - __morecore = &hugetlbfs_morecore;
> + if (__hugetlb_opts.thp_morecore)
> + __morecore = &thp_morecore;
> + else
> + __morecore = &hugetlbfs_morecore;
>
> /* Set some allocator options more appropriate for hugepages */
>
-Andrew Hastings
Cray Inc.
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