On Mon 20-10-14 19:12:04, Minchan Kim wrote:
> We don't need to split THP page when MADV_FREE syscall is
> called. It could be done when VM decide really frees it so
> we could avoid unnecessary THP split.
>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Other than a minor comment below
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> include/linux/huge_mm.h | 4 ++++
> mm/huge_memory.c | 35 +++++++++++++++++++++++++++++++++++
> mm/madvise.c | 21 ++++++++++++++++++++-
> mm/rmap.c | 8 ++++++--
> mm/vmscan.c | 28 ++++++++++++++++++----------
> 5 files changed, 83 insertions(+), 13 deletions(-)
>
[...]
> diff --git a/mm/madvise.c b/mm/madvise.c
> index a21584235bb6..84badee5f46d 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -271,8 +271,26 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> spinlock_t *ptl;
> pte_t *pte, ptent;
> struct page *page;
> + unsigned long next;
> +
> + next = pmd_addr_end(addr, end);
> + if (pmd_trans_huge(*pmd)) {
> + if (next - addr != HPAGE_PMD_SIZE) {
> +#ifdef CONFIG_DEBUG_VM
> + if (!rwsem_is_locked(&mm->mmap_sem)) {
> + pr_err("%s: mmap_sem is unlocked! addr=0x%lx end=0x%lx vma->vm_start=0x%lx vma->vm_end=0x%lx\n",
> + __func__, addr, end,
> + vma->vm_start,
> + vma->vm_end);
> + BUG();
> + }
> +#endif
Why is this code here? madvise_free_pte_range is called only from the
madvise path and we are holding mmap_sem and relying on that for regular
pages as well.
> + split_huge_page_pmd(vma, addr, pmd);
> + } else if (!madvise_free_huge_pmd(tlb, vma, pmd, addr))
> + goto next;
> + /* fall through */
> + }
>
> - split_huge_page_pmd(vma, addr, pmd);
> if (pmd_trans_unstable(pmd))
> return 0;
>
> @@ -316,6 +334,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> }
> arch_leave_lazy_mmu_mode();
> pte_unmap_unlock(pte - 1, ptl);
> +next:
> cond_resched();
> return 0;
> }
[...]
--
Michal Hocko
SUSE Labs
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