On Wed, Feb 17, 2016 at 01:13:26AM +0530, Vaishali Thakkar wrote:
> Currently incorrect default hugepage pool size is reported by proc
> nr_hugepages when number of pages for the default huge page size is
> specified twice.
>
> When multiple huge page sizes are supported, /proc/sys/vm/nr_hugepages
> indicates the current number of pre-allocated huge pages of the default
> size. Basically /proc/sys/vm/nr_hugepages displays default_hstate->
> max_huge_pages and after boot time pre-allocation, max_huge_pages should
> equal the number of pre-allocated pages (nr_hugepages).
>
> Test case:
>
> Note that this is specific to x86 architecture.
>
> Boot the kernel with command line option 'default_hugepagesz=1G
> hugepages=X hugepagesz=2M hugepages=Y hugepagesz=1G hugepages=Z'. After
> boot, 'cat /proc/sys/vm/nr_hugepages' and 'sysctl -a | grep hugepages'
> returns the value X. However, dmesg output shows that Z huge pages were
> pre-allocated.
>
> So, the root cause of the problem here is that the global variable
> default_hstate_max_huge_pages is set if a default huge page size is
> specified (directly or indirectly) on the command line. After the
> command line processing in hugetlb_init, if default_hstate_max_huge_pages
> is set, the value is assigned to default_hstae.max_huge_pages. However,
> default_hstate.max_huge_pages may have already been set based on the
> number of pre-allocated huge pages of default_hstate size.
>
> The solution to this problem is if hstate->max_huge_pages is already set
> then it should not set as a result of global max_huge_pages value.
> Basically if the value of the variable hugepages is set multiple times
> on a command line for a specific supported hugepagesize then proc layer
> should consider the last specified value.
>
> Signed-off-by: Vaishali Thakkar <vaishali.thakkar@xxxxxxxxxx>
Looks good to me.
Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> ---
> The patch contains one line over 80 characters as I think limiting that
> line to 80 characters makes code look bit ugly. But if anyone is having
> issue with that then I am fine with limiting it to 80 chracters.
> ---
> mm/hugetlb.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 06ae13e..01f2b48 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2630,8 +2630,10 @@ static int __init hugetlb_init(void)
> hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
> }
> default_hstate_idx = hstate_index(size_to_hstate(default_hstate_size));
> - if (default_hstate_max_huge_pages)
> - default_hstate.max_huge_pages = default_hstate_max_huge_pages;
> + if (default_hstate_max_huge_pages) {
> + if (!default_hstate.max_huge_pages)
> + default_hstate.max_huge_pages = default_hstate_max_huge_pages;
> + }
>
> hugetlb_init_hstates();
> gather_bootmem_prealloc();
> --
> 2.1.4
>
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