On Mon, Dec 01, 2014 at 02:04:42PM +0200, Shachar Raindel wrote:
> When do_wp_page is ending, in several cases it needs to unlock the
> pages and ptls it was accessing.
>
> Currently, this logic was "called" by using a goto jump. This makes
> following the control flow of the function harder. It is also
> against the coding style guidelines for using goto.
>
> As the code can easily be refactored into a specialized function,
> refactor it out and simplify the callsites code flow.
>
> Using goto for cleanup is generally allowed. However, extracting the
> cleanup to a separate function will allow deeper refactoring in the
> next patch.
>
> Signed-off-by: Shachar Raindel <raindel@xxxxxxxxxxxx>
> ---
> mm/memory.c | 66 +++++++++++++++++++++++++++++++++++++++++--------------------
> 1 file changed, 45 insertions(+), 21 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 61334e9..dd3bb13 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2089,6 +2089,40 @@ static int wp_page_reuse(struct mm_struct *mm, struct vm_area_struct *vma,
> }
>
> /*
> + * Release the ptl locking, as well as page references do_wp_page took.
> + *
> + * This function releases any locking and references remaining in the
> + * end of do_wp_page. The ptl lock is taken before do_wp_page is
> + * called. The old_page page reference is taken early in the execution
> + * of do_wp_page. However, in the OOM case we need to cleanup only the
> + * page-cache reference and not the ptl lock, which was dropped
> + * earlier. This results in highly assymetric release path.
> + */
> +static int wp_page_unlock(struct mm_struct *mm, struct vm_area_struct *vma,
> + pte_t *page_table, spinlock_t *ptl,
> + unsigned long mmun_start, unsigned long mmun_end,
> + struct page *old_page, int page_copied)
> + __releases(ptl)
> +{
> + pte_unmap_unlock(page_table, ptl);
> + if (mmun_end > mmun_start)
> + mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
> + if (old_page) {
> + /*
> + * Don't let another task, with possibly unlocked vma,
> + * keep the mlocked page.
> + */
> + if (page_copied && (vma->vm_flags & VM_LOCKED)) {
> + lock_page(old_page); /* LRU manipulation */
> + munlock_vma_page(old_page);
> + unlock_page(old_page);
> + }
> + page_cache_release(old_page);
> + }
> + return page_copied ? VM_FAULT_WRITE : 0;
> +}
> +
> +/*
> * This routine handles present pages, when users try to write
> * to a shared page. It is done by copying the page to a new address
> * and decrementing the shared-page counter for the old page.
> @@ -2113,7 +2147,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
> {
> struct page *old_page, *new_page = NULL;
> pte_t entry;
> - int ret = 0;
> + int page_copied = 0;
> unsigned long mmun_start = 0; /* For mmu_notifiers */
> unsigned long mmun_end = 0; /* For mmu_notifiers */
> struct mem_cgroup *memcg;
> @@ -2148,7 +2182,9 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
> &ptl);
> if (!pte_same(*page_table, orig_pte)) {
> unlock_page(old_page);
> - goto unlock;
> + return wp_page_unlock(mm, vma, page_table, ptl,
> + 0, 0,
> + old_page, 0);
For me, it makes code more cunfusing, not less.
Here we could just do something plain like:
pte_unmap_unlock(page_table, ptl);
page_cache_release(old_page);
return 0;
> }
> page_cache_release(old_page);
> }
> @@ -2193,7 +2229,9 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
> &ptl);
> if (!pte_same(*page_table, orig_pte)) {
> unlock_page(old_page);
> - goto unlock;
> + return wp_page_unlock(mm, vma, page_table, ptl,
> + 0, 0,
> + old_page, 0);
Ditto.
> }
>
> page_mkwrite = 1;
> @@ -2293,29 +2331,15 @@ gotten:
>
> /* Free the old page.. */
> new_page = old_page;
> - ret |= VM_FAULT_WRITE;
> + page_copied = 1;
> } else
> mem_cgroup_cancel_charge(new_page, memcg);
>
> if (new_page)
> page_cache_release(new_page);
> -unlock:
And now we don't need the label and can leave code in place.
> - pte_unmap_unlock(page_table, ptl);
> - if (mmun_end > mmun_start)
> - mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
> - if (old_page) {
> - /*
> - * Don't let another task, with possibly unlocked vma,
> - * keep the mlocked page.
> - */
> - if ((ret & VM_FAULT_WRITE) && (vma->vm_flags & VM_LOCKED)) {
> - lock_page(old_page); /* LRU manipulation */
> - munlock_vma_page(old_page);
> - unlock_page(old_page);
> - }
> - page_cache_release(old_page);
> - }
> - return ret;
> +
> + return wp_page_unlock(mm, vma, page_table, ptl, mmun_start,
> + mmun_end, old_page, page_copied);
> oom_free_new:
> page_cache_release(new_page);
> oom:
> --
> 1.7.11.2
>
> --
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--
Kirill A. Shutemov
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