On Wed, 26 Jan 2022, Pasha Tatashin wrote:
> Unify the code that flushes, clears pmd entry, and frees the PTE table
> level into a new function collapse_and_free_pmd().
>
> This clean-up is useful as in the next patch we will add another call to
> this function to iterate through PTE prior to freeing the level for page
> table check.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
One nit below.
> ---
> mm/khugepaged.c | 32 ++++++++++++++++----------------
> 1 file changed, 16 insertions(+), 16 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 35f14d0a00a6..440112355ffe 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1416,6 +1416,17 @@ static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
> return 0;
> }
>
> +static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
> + unsigned long addr, pmd_t *pmdp)
> +{
> + spinlock_t *ptl = pmd_lock(vma->vm_mm, pmdp);
> + pmd_t pmd = pmdp_collapse_flush(vma, addr, pmdp);
> +
> + spin_unlock(ptl);
No strong objection, but I think the typical style would be to declare the
local variables separately and avoid mixing the code, especially in cases
when taking locks (and not just initializing the local variables).
> + mm_dec_nr_ptes(mm);
> + pte_free(mm, pmd_pgtable(pmd));
> +}
> +
> /**
> * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
> * address haddr.
> @@ -1433,7 +1444,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
> struct vm_area_struct *vma = find_vma(mm, haddr);
> struct page *hpage;
> pte_t *start_pte, *pte;
> - pmd_t *pmd, _pmd;
> + pmd_t *pmd;
> spinlock_t *ptl;
> int count = 0;
> int i;
> @@ -1509,12 +1520,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
> }
>
> /* step 4: collapse pmd */
> - ptl = pmd_lock(vma->vm_mm, pmd);
> - _pmd = pmdp_collapse_flush(vma, haddr, pmd);
> - spin_unlock(ptl);
> - mm_dec_nr_ptes(mm);
> - pte_free(mm, pmd_pgtable(_pmd));
> -
> + collapse_and_free_pmd(mm, vma, haddr, pmd);
> drop_hpage:
> unlock_page(hpage);
> put_page(hpage);
> @@ -1552,7 +1558,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
> struct vm_area_struct *vma;
> struct mm_struct *mm;
> unsigned long addr;
> - pmd_t *pmd, _pmd;
> + pmd_t *pmd;
>
> i_mmap_lock_write(mapping);
> vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
> @@ -1591,14 +1597,8 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
> * reverse order. Trylock is a way to avoid deadlock.
> */
> if (mmap_write_trylock(mm)) {
> - if (!khugepaged_test_exit(mm)) {
> - spinlock_t *ptl = pmd_lock(mm, pmd);
> - /* assume page table is clear */
> - _pmd = pmdp_collapse_flush(vma, addr, pmd);
> - spin_unlock(ptl);
> - mm_dec_nr_ptes(mm);
> - pte_free(mm, pmd_pgtable(_pmd));
> - }
> + if (!khugepaged_test_exit(mm))
> + collapse_and_free_pmd(mm, vma, addr, pmd);
> mmap_write_unlock(mm);
> } else {
> /* Try again later */
> --
> 2.35.0.rc0.227.g00780c9af4-goog
>
>
