| Message ID | 1455182907-15445-2-git-send-email-vgupta@synopsys.com |
|---|---|
| State | New |
| Headers | show |
On Thu, 11 Feb 2016 14:58:26 +0530 Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote: > Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw() > assume pgtable_t to be struct page * which is not true for all arches. > Thus arc, s390, sparch end up with their own copies despite no special > hardware requirements (unlike powerpc). s390 does have a special hardware requirement. pgtable_t is an address for a 2K block of memory. It is *not* equivalent to a struct page * which refers to a 4K block of memory. That has been the whole point to introduce pgtable_t. > It seems massaging the code a bit can make it reusbale. Imho the new code for asm-generic looks fine, as long as the override with __HAVE_ARCH_PGTABLE_DEPOSIT/__HAVE_ARCH_PGTABLE_WITHDRAW continues to work I do not mind.
On Thursday 11 February 2016 03:52 PM, Martin Schwidefsky wrote: > On Thu, 11 Feb 2016 14:58:26 +0530 > Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote: > >> Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw() >> assume pgtable_t to be struct page * which is not true for all arches. >> Thus arc, s390, sparch end up with their own copies despite no special >> hardware requirements (unlike powerpc). > > s390 does have a special hardware requirement. pgtable_t is an address > for a 2K block of memory. It is *not* equivalent to a struct page * > which refers to a 4K block of memory. That has been the whole point > to introduce pgtable_t. Actually my reference to hardware requirement was more like powerpc style save a hash value some where etc. Now pgtable_t need not be struct page * even if the actual sizes are same - e.g. in ARC port I kept pgtable_t as pte_t * simply to avoid a few page_address() calls in mm code (you could argue that is was a micro-optimization, anyways..) So given I know nothing about s390 MMU internals, I still think you can switch to the update generic version despite 2K vs. 4K. Agree ? >> It seems massaging the code a bit can make it reusbale. > > Imho the new code for asm-generic looks fine, as long as the override > with __HAVE_ARCH_PGTABLE_DEPOSIT/__HAVE_ARCH_PGTABLE_WITHDRAW continues > to work I do not mind.
On Thu, 11 Feb 2016 16:23:33 +0530 Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote: > On Thursday 11 February 2016 03:52 PM, Martin Schwidefsky wrote: > > On Thu, 11 Feb 2016 14:58:26 +0530 > > Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote: > > > >> Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw() > >> assume pgtable_t to be struct page * which is not true for all arches. > >> Thus arc, s390, sparch end up with their own copies despite no special > >> hardware requirements (unlike powerpc). > > > > s390 does have a special hardware requirement. pgtable_t is an address > > for a 2K block of memory. It is *not* equivalent to a struct page * > > which refers to a 4K block of memory. That has been the whole point > > to introduce pgtable_t. > > Actually my reference to hardware requirement was more like powerpc style save a > hash value some where etc. > > Now pgtable_t need not be struct page * even if the actual sizes are same - e.g. > in ARC port I kept pgtable_t as pte_t * simply to avoid a few page_address() calls > in mm code (you could argue that is was a micro-optimization, anyways..) > > So given I know nothing about s390 MMU internals, I still think you can switch to > the update generic version despite 2K vs. 4K. Agree ? No, we can not. For s390 a page table is aligned on a 2K boundary and is only half the size of a page (except for KVM but that is another story). For s390 a pgtable_t is a pointer to the memory location with the 256 ptes and not a struct page *. The cast "struct page *new = (struct page*)pgtable;" in your first patch is already broken, "new" points to the memory of the page table and the list_head operations will clobber that memory. You try to fix it up with the memset to zero in pgtable_trans_huge_withdraw but that does not correct the pte entries for s390 as an invalid page-table entry is *not* all zeros. In short, please let s390 keep its own copy of deposit/withdraw.
On Thursday 11 February 2016 04:50 PM, Martin Schwidefsky wrote: > On Thu, 11 Feb 2016 16:23:33 +0530 > Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote: > >> On Thursday 11 February 2016 03:52 PM, Martin Schwidefsky wrote: >>> On Thu, 11 Feb 2016 14:58:26 +0530 >>> Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote: >>> >>>> Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw() >>>> assume pgtable_t to be struct page * which is not true for all arches. >>>> Thus arc, s390, sparch end up with their own copies despite no special >>>> hardware requirements (unlike powerpc). >>> >>> s390 does have a special hardware requirement. pgtable_t is an address >>> for a 2K block of memory. It is *not* equivalent to a struct page * >>> which refers to a 4K block of memory. That has been the whole point >>> to introduce pgtable_t. >> >> Actually my reference to hardware requirement was more like powerpc style save a >> hash value some where etc. >> >> Now pgtable_t need not be struct page * even if the actual sizes are same - e.g. >> in ARC port I kept pgtable_t as pte_t * simply to avoid a few page_address() calls >> in mm code (you could argue that is was a micro-optimization, anyways..) >> >> So given I know nothing about s390 MMU internals, I still think you can switch to >> the update generic version despite 2K vs. 4K. Agree ? > > No, we can not. For s390 a page table is aligned on a 2K boundary and is > only half the size of a page (except for KVM but that is another story). > For s390 a pgtable_t is a pointer to the memory location with the 256 ptes > and not a struct page *. > > The cast "struct page *new = (struct page*)pgtable;" in your first patch > is already broken, "new" points to the memory of the page table and > the list_head operations will clobber that memory. The current s390 code does something similar using a different struct cast. It is still writing in pgtable_t - although at a different location. > You try to fix it up > with the memset to zero in pgtable_trans_huge_withdraw but that does not > correct the pte entries for s390 as an invalid page-table entry is *not* > all zeros. Right so that is the problem - just trying to understand. > In short, please let s390 keep its own copy of deposit/withdraw. You got it - I'm out of the way :-) Thx, -Vineet
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c index 75664ed7e3ab..c9f2f6f8c7bb 100644 --- a/mm/pgtable-generic.c +++ b/mm/pgtable-generic.c @@ -155,13 +155,17 @@ void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address, void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp, pgtable_t pgtable) { + struct page *new = (struct page *)pgtable; + struct page *head; + assert_spin_locked(pmd_lockptr(mm, pmdp)); /* FIFO */ - if (!pmd_huge_pte(mm, pmdp)) - INIT_LIST_HEAD(&pgtable->lru); + head = (struct page *)pmd_huge_pte(mm, pmdp); + if (!head) + INIT_LIST_HEAD(&new->lru); else - list_add(&pgtable->lru, &pmd_huge_pte(mm, pmdp)->lru); + list_add(&new->lru, &head->lru); pmd_huge_pte(mm, pmdp) = pgtable; } #endif @@ -170,20 +174,23 @@ void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp, /* no "address" argument so destroys page coloring of some arch */ pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp) { - pgtable_t pgtable; + struct page *page; assert_spin_locked(pmd_lockptr(mm, pmdp)); + page = (struct page *)pmd_huge_pte(mm, pmdp); + /* FIFO */ - pgtable = pmd_huge_pte(mm, pmdp); - if (list_empty(&pgtable->lru)) + if (list_empty(&page->lru)) pmd_huge_pte(mm, pmdp) = NULL; else { - pmd_huge_pte(mm, pmdp) = list_entry(pgtable->lru.next, - struct page, lru); - list_del(&pgtable->lru); + pmd_huge_pte(mm, pmdp) = (pgtable_t) list_entry(page->lru.next, + struct page, lru); + list_del(&page->lru); } - return pgtable; + + memset(&page->lru, 0, sizeof(page->lru)); + return (pgtable_t)page; } #endif
Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw() assume pgtable_t to be struct page * which is not true for all arches. Thus arc, s390, sparch end up with their own copies despite no special hardware requirements (unlike powerpc). It seems massaging the code a bit can make it reusbale. - Use explicit casts to (struct page *). For existing users, this should be semantically no-op for existing users - The only addition is zero'ing out of page->lru which for arc leaves a stray entry in pgtable_t cause mm spew when such pgtable is freed. | huge_memory: BUG: failure at | ../mm/huge_memory.c:1858/__split_huge_page_map()! | CPU: 0 PID: 901 Comm: bw_mem Not tainted 4.4.0-00015-g0569c1459cfa-dirty | | Stack Trace: | arc_unwind_core.constprop.1+0x94/0x104 | split_huge_page_to_list+0x5c0/0x920 | __split_huge_page_pmd+0xc8/0x1b4 | vma_adjust_trans_huge+0x104/0x1c8 | vma_adjust+0xf8/0x6d8 | __split_vma.isra.40+0xf8/0x174 | do_munmap+0x360/0x428 | SyS_munmap+0x28/0x44 Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: David S. Miller <davem@davemloft.net> Cc: Alex Thorlton <athorlton@sgi.com> Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: linux-snps-arc@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-arch@vger.kernel.org Signed-off-by: Vineet Gupta <vgupta@synopsys.com> --- mm/pgtable-generic.c | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-)