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Date:      Wed, 2 Aug 2023 11:23:48 +0200
From:      tuexen@fh-muenster.de
To:        Dmitry Chagin <dchagin@freebsd.org>
Cc:        Doug Moore <dougm@freebsd.org>, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org, src-committers@freebsd.org
Subject:   Re: git: 1a7fcf6d51eb - main - vm_phys_enqueue_contig: handle npages==0
Message-ID:  <B6B2B80C-3633-4041-AD13-ABCED4F3A3C4@fh-muenster.de>
In-Reply-To: <CAC0jpUCEyN0STBvuqv2kcvV8NY04RXGdszEf2MS6pJKC3bf8Kw@mail.gmail.com>
References:  <202308020314.3723ETgj027830@gitrepo.freebsd.org> <CAC0jpUCEyN0STBvuqv2kcvV8NY04RXGdszEf2MS6pJKC3bf8Kw@mail.gmail.com>

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[-- Attachment #1 --]
> On 2. Aug 2023, at 10:15, Dmitry Chagin <dchagin@freebsd.org> wrote:
> 
> 
> Hi,
> 
> With this change, I got a panic:
> vm_phys_enq_range: page 0xfffffe0000000000 and pages 0 are misaligned
My arm64 system also panics:

panic: vm_phys_enq_range: page 0xffffa000796a7000 and npages 4294443008 are misaligned

Best regards
Michael
> 
> Ср, 2 авг. 2023 г. в 06:22, Doug Moore <dougm@freebsd.org>:
> The branch main has been updated by dougm:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=1a7fcf6d51eb67ee3e05fdbb806f7e68f9f53c9c
> 
> commit 1a7fcf6d51eb67ee3e05fdbb806f7e68f9f53c9c
> Author:     Doug Moore <dougm@FreeBSD.org>
> AuthorDate: 2023-08-02 03:12:00 +0000
> Commit:     Doug Moore <dougm@FreeBSD.org>
> CommitDate: 2023-08-02 03:12:00 +0000
> 
>     vm_phys_enqueue_contig: handle npages==0
> 
>     By letting vm_phys_enqueue_contig handle the case when npages == 0,
>     the callers can stop checking it, and the compiler can stop
>     zero-checking with every call to ffs(). Letting vm_phys_enqueue_contig
>     call vm_phys_enqueue_contig for part of its work also saves a few
>     bytes.
> 
>     The amd64 object code shrinks by 80 bytes.
> 
>     Reviewed by:    kib
>     Differential Revision:  https://reviews.freebsd.org/D41154
> ---
>  sys/vm/vm_phys.c | 74 +++++++++++++++++++++++++++-----------------------------
>  1 file changed, 35 insertions(+), 39 deletions(-)
> 
> diff --git a/sys/vm/vm_phys.c b/sys/vm/vm_phys.c
> index 28f12231e01c..b2084bdef4e1 100644
> --- a/sys/vm/vm_phys.c
> +++ b/sys/vm/vm_phys.c
> @@ -72,6 +72,8 @@ __FBSDID("$FreeBSD$");
> 
>  _Static_assert(sizeof(long) * NBBY >= VM_PHYSSEG_MAX,
>      "Too many physsegs.");
> +_Static_assert(sizeof(long long) >= sizeof(vm_paddr_t),
> +    "vm_paddr_t too big for ffsll, flsll.");
> 
>  #ifdef NUMA
>  struct mem_affinity __read_mostly *mem_affinity;
> @@ -690,18 +692,16 @@ vm_phys_split_pages(vm_page_t m, int oind, struct vm_freelist *fl, int order,
>   *
>   * The physical page m's buddy must not be free.
>   */
> -static void
> +static vm_page_t
>  vm_phys_enq_range(vm_page_t m, u_int npages, struct vm_freelist *fl, int tail)
>  {
> -       u_int n;
>         int order;
> 
> -       KASSERT(npages > 0, ("vm_phys_enq_range: npages is 0"));
>         KASSERT(((VM_PAGE_TO_PHYS(m) + npages * PAGE_SIZE) &
>             ((PAGE_SIZE << (fls(npages) - 1)) - 1)) == 0,
>             ("vm_phys_enq_range: page %p and npages %u are misaligned",
>             m, npages));
> -       do {
> +       while (npages > 0) {
>                 KASSERT(m->order == VM_NFREEORDER,
>                     ("vm_phys_enq_range: page %p has unexpected order %d",
>                     m, m->order));
> @@ -709,10 +709,10 @@ vm_phys_enq_range(vm_page_t m, u_int npages, struct vm_freelist *fl, int tail)
>                 KASSERT(order < VM_NFREEORDER,
>                     ("vm_phys_enq_range: order %d is out of range", order));
>                 vm_freelist_add(fl, m, order, tail);
> -               n = 1 << order;
> -               m += n;
> -               npages -= n;
> -       } while (npages > 0);
> +               m += 1 << order;
> +               npages -= 1 << order;
> +       }
> +       return (m);
>  }
> 
>  /*
> @@ -744,7 +744,7 @@ vm_phys_alloc_npages(int domain, int pool, int npages, vm_page_t ma[])
>  {
>         struct vm_freelist *alt, *fl;
>         vm_page_t m;
> -       int avail, end, flind, freelist, i, need, oind, pind;
> +       int avail, end, flind, freelist, i, oind, pind;
> 
>         KASSERT(domain >= 0 && domain < vm_ndomains,
>             ("vm_phys_alloc_npages: domain %d is out of range", domain));
> @@ -762,20 +762,18 @@ vm_phys_alloc_npages(int domain, int pool, int npages, vm_page_t ma[])
>                 for (oind = 0; oind < VM_NFREEORDER; oind++) {
>                         while ((m = TAILQ_FIRST(&fl[oind].pl)) != NULL) {
>                                 vm_freelist_rem(fl, m, oind);
> -                               avail = 1 << oind;
> -                               need = imin(npages - i, avail);
> -                               for (end = i + need; i < end;)
> +                               avail = i + (1 << oind);
> +                               end = imin(npages, avail);
> +                               while (i < end)
>                                         ma[i++] = m++;
> -                               if (need < avail) {
> +                               if (i == npages) {
>                                         /*
> -                                        * Return excess pages to fl.  Its
> -                                        * order [0, oind) queues are empty.
> +                                        * Return excess pages to fl.  Its order
> +                                        * [0, oind) queues are empty.
>                                          */
> -                                       vm_phys_enq_range(m, avail - need, fl,
> -                                           1);
> -                                       return (npages);
> -                               } else if (i == npages)
> +                                       vm_phys_enq_range(m, avail - i, fl, 1);
>                                         return (npages);
> +                               }
>                         }
>                 }
>                 for (oind = VM_NFREEORDER - 1; oind >= 0; oind--) {
> @@ -785,21 +783,20 @@ vm_phys_alloc_npages(int domain, int pool, int npages, vm_page_t ma[])
>                                     NULL) {
>                                         vm_freelist_rem(alt, m, oind);
>                                         vm_phys_set_pool(pool, m, oind);
> -                                       avail = 1 << oind;
> -                                       need = imin(npages - i, avail);
> -                                       for (end = i + need; i < end;)
> +                                       avail = i + (1 << oind);
> +                                       end = imin(npages, avail);
> +                                       while (i < end)
>                                                 ma[i++] = m++;
> -                                       if (need < avail) {
> +                                       if (i == npages) {
>                                                 /*
>                                                  * Return excess pages to fl.
>                                                  * Its order [0, oind) queues
>                                                  * are empty.
>                                                  */
> -                                               vm_phys_enq_range(m, avail -
> -                                                   need, fl, 1);
> -                                               return (npages);
> -                                       } else if (i == npages)
> +                                               vm_phys_enq_range(m, avail - i,
> +                                                   fl, 1);
>                                                 return (npages);
> +                                       }
>                                 }
>                         }
>                 }
> @@ -1146,7 +1143,7 @@ max_order(vm_page_t m)
>          * because the size of a physical address exceeds the size of
>          * a long.
>          */
> -       return (min(ffsl(VM_PAGE_TO_PHYS(m) >> PAGE_SHIFT) - 1,
> +       return (min(ffsll(VM_PAGE_TO_PHYS(m) >> PAGE_SHIFT) - 1,
>             VM_NFREEORDER - 1));
>  }
> 
> @@ -1162,6 +1159,7 @@ vm_phys_enqueue_contig(vm_page_t m, u_long npages)
>         struct vm_freelist *fl;
>         struct vm_phys_seg *seg;
>         vm_page_t m_end;
> +       vm_paddr_t diff, lo;
>         int order;
> 
>         /*
> @@ -1173,15 +1171,15 @@ vm_phys_enqueue_contig(vm_page_t m, u_long npages)
>         fl = (*seg->free_queues)[m->pool];
>         m_end = m + npages;
>         /* Free blocks of increasing size. */
> -       while ((order = max_order(m)) < VM_NFREEORDER - 1 &&
> -           m + (1 << order) <= m_end) {
> -               KASSERT(seg == &vm_phys_segs[m->segind],
> -                   ("%s: page range [%p,%p) spans multiple segments",
> -                   __func__, m_end - npages, m));
> -               vm_freelist_add(fl, m, order, 1);
> -               m += 1 << order;
> +       lo = VM_PAGE_TO_PHYS(m) >> PAGE_SHIFT;
> +       if (m < m_end &&
> +           (diff = lo ^ (lo + npages - 1)) != 0) {
> +               order = min(flsll(diff) - 1, VM_NFREEORDER - 1);
> +               m = vm_phys_enq_range(m, roundup2(-lo, 1 << order), fl, 1);
>         }
> +
>         /* Free blocks of maximum size. */
> +       order = VM_NFREEORDER - 1;
>         while (m + (1 << order) <= m_end) {
>                 KASSERT(seg == &vm_phys_segs[m->segind],
>                     ("%s: page range [%p,%p) spans multiple segments",
> @@ -1560,10 +1558,8 @@ vm_phys_alloc_contig(int domain, u_long npages, vm_paddr_t low, vm_paddr_t high,
>                         vm_phys_set_pool(VM_FREEPOOL_DEFAULT, m, oind);
>         }
>         /* Return excess pages to the free lists. */
> -       if (&m_run[npages] < m) {
> -               fl = (*queues)[VM_FREEPOOL_DEFAULT];
> -               vm_phys_enq_range(&m_run[npages], m - &m_run[npages], fl, 0);
> -       }
> +       fl = (*queues)[VM_FREEPOOL_DEFAULT];
> +       vm_phys_enq_range(&m_run[npages], m - &m_run[npages], fl, 0);
>         return (m_run);
>  }
> 


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