On 03/28/2016 08:50 PM, Hillf Danton wrote:
>>
>> When creating a hugetlb mapping, attempt PUD_SIZE alignment if the
>> following conditions are met:
>> - Address passed to mmap or shmat is NULL
>> - The mapping is flaged as shared
>> - The mapping is at least PUD_SIZE in length
>> If a PUD_SIZE aligned mapping can not be created, then fall back to a
>> huge page size mapping.
>>
>> Signed-off-by: Mike Kravetz <mike.krav...@oracle.com>
>> ---
>> fs/hugetlbfs/inode.c | 29 +++++++++++++++++++++++++++--
>> 1 file changed, 27 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>> index 540ddc9..22b2e38 100644
>> --- a/fs/hugetlbfs/inode.c
>> +++ b/fs/hugetlbfs/inode.c
>> @@ -175,6 +175,17 @@ hugetlb_get_unmapped_area(struct file *file, unsigned
>> long addr,
>> struct vm_area_struct *vma;
>> struct hstate *h = hstate_file(file);
>> struct vm_unmapped_area_info info;
>> + bool pud_size_align = false;
>> + unsigned long ret_addr;
>> +
>> + /*
>> + * If PMD sharing is enabled, align to PUD_SIZE to facilitate
>> + * sharing. Only attempt alignment if no address was passed in,
>> + * flags indicate sharing and size is big enough.
>> + */
>> + if (IS_ENABLED(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) &&
>> + !addr && flags & MAP_SHARED && len >= PUD_SIZE)
>> + pud_size_align = true;
>>
>> if (len & ~huge_page_mask(h))
>> return -EINVAL;
>> @@ -199,9 +210,23 @@ hugetlb_get_unmapped_area(struct file *file, unsigned
>> long addr,
>> info.length = len;
>> info.low_limit = TASK_UNMAPPED_BASE;
>> info.high_limit = TASK_SIZE;
>> - info.align_mask = PAGE_MASK & ~huge_page_mask(h);
>> + if (pud_size_align)
>> + info.align_mask = PAGE_MASK & (PUD_SIZE - 1);
>> + else
>> + info.align_mask = PAGE_MASK & ~huge_page_mask(h);
>> info.align_offset = 0;
>> - return vm_unmapped_area(&info);
>> + ret_addr = vm_unmapped_area(&info);
>> +
>> + /*
>> + * If failed with PUD_SIZE alignment, try again with huge page
>> + * size alignment.
>> + */
>
> Can we avoid going another round as long as it is a file with
> the PUD page size?
Yes, that brings up a good point.
Since we only do PMD sharing with PMD_SIZE huge pages, that should be
part of the check as to whether we try PUD_SIZE alignment. The initial
check should be expanded as follows:
if (IS_ENABLED(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) && !addr &&
flags & MAP_SHARED && huge_page_size(h) == PMD_SIZE && len >= PUD_SIZE)
pud_size_align = true;
In that case, pud_size_align remains false and we do not retry.
--
Mike Kravetz
>
> Hillf
>> + if ((ret_addr & ~PAGE_MASK) && pud_size_align) {
>> + info.align_mask = PAGE_MASK & ~huge_page_mask(h);
>> + ret_addr = vm_unmapped_area(&info);
>> + }
>> +
>> + return ret_addr;
>> }
>> #endif
>>
>> --
>> 2.4.3
>
