| Message ID | 20191115055340.1825745-3-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/gup: track dma-pinned pages: FOLL_PIN | expand |
On Thu 14-11-19 21:53:18, 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. > > Reviewed-by: Jérôme Glisse <jglisse@redhat.com> > Cc: Jan Kara <jack@suse.cz> > Cc: Ira Weiny <ira.weiny@intel.com> > 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 | 95 ++++++++++++++++++++++++-------------------------------- > 1 file changed, 40 insertions(+), 55 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 85caf76b3012..858541ea30ce 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1969,6 +1969,29 @@ 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 = 0; > + int nr_recorded_pages = 0; > + > + do { > + pages[nr] = page; > + nr++; > + page++; > + nr_recorded_pages++; > + } while (addr += PAGE_SIZE, addr != end); > + return nr_recorded_pages; nr == nr_recorded_pages so no need for both... BTW, structuring this as a for loop would be probably more logical and shorter now: for (nr = 0; addr != end; addr += PAGE_SIZE) pages[nr++] = page++; return nr; The rest of the patch looks good to me. Honza
On 11/18/19 1:46 AM, Jan Kara wrote: > On Thu 14-11-19 21:53:18, 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. >> >> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> >> Cc: Jan Kara <jack@suse.cz> >> Cc: Ira Weiny <ira.weiny@intel.com> >> 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 | 95 ++++++++++++++++++++++++-------------------------------- >> 1 file changed, 40 insertions(+), 55 deletions(-) >> >> diff --git a/mm/gup.c b/mm/gup.c >> index 85caf76b3012..858541ea30ce 100644 >> --- a/mm/gup.c >> +++ b/mm/gup.c >> @@ -1969,6 +1969,29 @@ 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 = 0; >> + int nr_recorded_pages = 0; >> + >> + do { >> + pages[nr] = page; >> + nr++; >> + page++; >> + nr_recorded_pages++; >> + } while (addr += PAGE_SIZE, addr != end); >> + return nr_recorded_pages; > > nr == nr_recorded_pages so no need for both... BTW, structuring this as a > for loop would be probably more logical and shorter now: > > for (nr = 0; addr != end; addr += PAGE_SIZE) > pages[nr++] = page++; > return nr; > Nice touch, I've applied it. thanks,
diff --git a/mm/gup.c b/mm/gup.c index 85caf76b3012..858541ea30ce 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1969,6 +1969,29 @@ 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 = 0; + 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); +} + #ifdef CONFIG_ARCH_HAS_HUGEPD static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end, unsigned long sz) @@ -1998,32 +2021,20 @@ 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; } + *nr += refs; SetPageReferenced(head); return 1; } @@ -2071,28 +2082,19 @@ 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; } + *nr += refs; SetPageReferenced(head); return 1; } @@ -2114,28 +2116,19 @@ 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; } + *nr += refs; SetPageReferenced(head); return 1; } @@ -2151,28 +2144,20 @@ 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; } + *nr += refs; SetPageReferenced(head); return 1; }