On Wed, Oct 30, 2019 at 03:49:13PM -0700, 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.
Overall it seems like a pretty good clean up. It did take a bit of review but I _think_ it is correct. A couple of comments below.
Cc: Christoph Hellwig hch@lst.de Cc: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Signed-off-by: John Hubbard jhubbard@nvidia.com
mm/gup.c | 113 ++++++++++++++++++++++--------------------------------- 1 file changed, 46 insertions(+), 67 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c index 85caf76b3012..8fb0d9cdfaf5 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1969,6 +1969,35 @@ 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 __remove_refs_from_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);
+}
I wonder if this is better implemented as "put_compound_head()"? To match the try_get_compound_head() call below?
+static int __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr) +{
- *nr += nr_recorded_pages;
- SetPageReferenced(head);
- return 1;
When will this return anything but 1?
Ira
+}
#ifdef CONFIG_ARCH_HAS_HUGEPD static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end, unsigned long sz) @@ -1998,34 +2027,19 @@ 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);
__remove_refs_from_head(head, refs);
- SetPageReferenced(head);
- return 1;
- return __huge_pt_done(head, refs, nr);
} static int gup_huge_pd(hugepd_t hugepd, unsigned long addr, @@ -2071,30 +2085,18 @@ 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);
__remove_refs_from_head(head, refs);
- SetPageReferenced(head);
- return 1;
- return __huge_pt_done(head, refs, nr);
} static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, @@ -2114,30 +2116,18 @@ 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);
__remove_refs_from_head(head, refs);
- SetPageReferenced(head);
- return 1;
- return __huge_pt_done(head, refs, nr);
} static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, @@ -2151,30 +2141,19 @@ 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);
__remove_refs_from_head(head, refs);
- SetPageReferenced(head);
- return 1;
- return __huge_pt_done(head, refs, nr);
} static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, -- 2.23.0