On Sun, Nov 03, 2019 at 01:17:57PM -0800, John Hubbard wrote:
> There are four locations in gup.c that have a fair amount of code
> duplication. This means that changing one requires making the same
> changes in four places, not to mention reading the same code four
> times, and wondering if there are subtle differences.
>
> Factor out the common code into static functions, thus reducing the
> overall line count and the code's complexity.
>
> Also, take the opportunity to slightly improve the efficiency of the
> error cases, by doing a mass subtraction of the refcount, surrounded
> by get_page()/put_page().
>
> Also, further simplify (slightly), by waiting until the the successful
> end of each routine, to increment *nr.
>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Good cleanup.
Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> ---
> mm/gup.c | 104 ++++++++++++++++++++++++-------------------------------
> 1 file changed, 45 insertions(+), 59 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 85caf76b3012..199da99e8ffc 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1969,6 +1969,34 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
> }
> #endif
>
> +static int __record_subpages(struct page *page, unsigned long addr,
> + unsigned long end, struct page **pages, int nr)
> +{
> + int nr_recorded_pages = 0;
> +
> + do {
> + pages[nr] = page;
> + nr++;
> + page++;
> + nr_recorded_pages++;
> + } while (addr += PAGE_SIZE, addr != end);
> + return nr_recorded_pages;
> +}
> +
> +static void put_compound_head(struct page *page, int refs)
> +{
> + /* Do a get_page() first, in case refs == page->_refcount */
> + get_page(page);
> + page_ref_sub(page, refs);
> + put_page(page);
> +}
> +
> +static void __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr)
> +{
> + *nr += nr_recorded_pages;
> + SetPageReferenced(head);
> +}
> +
> #ifdef CONFIG_ARCH_HAS_HUGEPD
> static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
> unsigned long sz)
> @@ -1998,33 +2026,20 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> /* hugepages are never "special" */
> VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
>
> - refs = 0;
> head = pte_page(pte);
> -
> page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
> - do {
> - VM_BUG_ON(compound_head(page) != head);
> - pages[*nr] = page;
> - (*nr)++;
> - page++;
> - refs++;
> - } while (addr += PAGE_SIZE, addr != end);
> + refs = __record_subpages(page, addr, end, pages, *nr);
>
> head = try_get_compound_head(head, refs);
> - if (!head) {
> - *nr -= refs;
> + if (!head)
> return 0;
> - }
>
> if (unlikely(pte_val(pte) != pte_val(*ptep))) {
> - /* Could be optimized better */
> - *nr -= refs;
> - while (refs--)
> - put_page(head);
> + put_compound_head(head, refs);
> return 0;
> }
>
> - SetPageReferenced(head);
> + __huge_pt_done(head, refs, nr);
> return 1;
> }
>
> @@ -2071,29 +2086,19 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> pages, nr);
> }
>
> - refs = 0;
> page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> - do {
> - pages[*nr] = page;
> - (*nr)++;
> - page++;
> - refs++;
> - } while (addr += PAGE_SIZE, addr != end);
> + refs = __record_subpages(page, addr, end, pages, *nr);
>
> head = try_get_compound_head(pmd_page(orig), refs);
> - if (!head) {
> - *nr -= refs;
> + if (!head)
> return 0;
> - }
>
> if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
> - *nr -= refs;
> - while (refs--)
> - put_page(head);
> + put_compound_head(head, refs);
> return 0;
> }
>
> - SetPageReferenced(head);
> + __huge_pt_done(head, refs, nr);
> return 1;
> }
>
> @@ -2114,29 +2119,19 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> pages, nr);
> }
>
> - refs = 0;
> page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> - do {
> - pages[*nr] = page;
> - (*nr)++;
> - page++;
> - refs++;
> - } while (addr += PAGE_SIZE, addr != end);
> + refs = __record_subpages(page, addr, end, pages, *nr);
>
> head = try_get_compound_head(pud_page(orig), refs);
> - if (!head) {
> - *nr -= refs;
> + if (!head)
> return 0;
> - }
>
> if (unlikely(pud_val(orig) != pud_val(*pudp))) {
> - *nr -= refs;
> - while (refs--)
> - put_page(head);
> + put_compound_head(head, refs);
> return 0;
> }
>
> - SetPageReferenced(head);
> + __huge_pt_done(head, refs, nr);
> return 1;
> }
>
> @@ -2151,29 +2146,20 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> return 0;
>
> BUILD_BUG_ON(pgd_devmap(orig));
> - refs = 0;
> +
> page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
> - do {
> - pages[*nr] = page;
> - (*nr)++;
> - page++;
> - refs++;
> - } while (addr += PAGE_SIZE, addr != end);
> + refs = __record_subpages(page, addr, end, pages, *nr);
>
> head = try_get_compound_head(pgd_page(orig), refs);
> - if (!head) {
> - *nr -= refs;
> + if (!head)
> return 0;
> - }
>
> if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
> - *nr -= refs;
> - while (refs--)
> - put_page(head);
> + put_compound_head(head, refs);
> return 0;
> }
>
> - SetPageReferenced(head);
> + __huge_pt_done(head, refs, nr);
> return 1;
> }
>
> --
> 2.23.0
>
