• Larry Woodman's avatar
    fix hugepages leak due to pagetable page sharing · c5c99429
    Larry Woodman authored
    
    
    The shared page table code for hugetlb memory on x86 and x86_64
    is causing a leak.  When a user of hugepages exits using this code
    the system leaks some of the hugepages.
    
    -------------------------------------------------------
    Part of /proc/meminfo just before database startup:
    HugePages_Total:  5500
    HugePages_Free:   5500
    HugePages_Rsvd:      0
    Hugepagesize:     2048 kB
    
    Just before shutdown:
    HugePages_Total:  5500
    HugePages_Free:   4475
    HugePages_Rsvd:      0
    Hugepagesize:     2048 kB
    
    After shutdown:
    HugePages_Total:  5500
    HugePages_Free:   4988
    HugePages_Rsvd:
    0 Hugepagesize:     2048 kB
    ----------------------------------------------------------
    
    The problem occurs durring a fork, in copy_hugetlb_page_range().  It
    locates the dst_pte using huge_pte_alloc().  Since huge_pte_alloc() calls
    huge_pmd_share() it will share the pmd page if can, yet the main loop in
    copy_hugetlb_page_range() does a get_page() on every hugepage.  This is a
    violation of the shared hugepmd pagetable protocol and creates additional
    referenced to the hugepages causing a leak when the unmap of the VMA
    occurs.  We can skip the entire replication of the ptes when the hugepage
    pagetables are shared.  The attached patch skips copying the ptes and the
    get_page() calls if the hugetlbpage pagetable is shared.
    
    [akpm@linux-foundation.org: coding-style cleanups]
    Signed-off-by: default avatarLarry Woodman <lwoodman@redhat.com>
    Signed-off-by: default avatarAdam Litke <agl@us.ibm.com>
    Cc: Badari Pulavarty <pbadari@us.ibm.com>
    Cc: Ken Chen <kenchen@google.com>
    Cc: David Gibson <david@gibson.dropbear.id.au>
    Cc: William Lee Irwin III <wli@holomorphy.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    c5c99429