Re: [PATCH v1 04/11] mm/memremap: add ZONE_DEVICE support for compound pages

[Joao Martins <joao.m.martins@oracle.com>]

On 5/5/21 7:44 PM, Dan Williams wrote:
> On Thu, Mar 25, 2021 at 4:10 PM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> Add a new align property for struct dev_pagemap which specifies that a
>> pagemap is composed of a set of compound pages of size @align, instead
>> of base pages. When these pages are initialised, most are initialised as
>> tail pages instead of order-0 pages.
>>
>> For certain ZONE_DEVICE users like device-dax which have a fixed page
>> size, this creates an opportunity to optimize GUP and GUP-fast walkers,
>> treating it the same way as THP or hugetlb pages.
>>
>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>> ---
>>  include/linux/memremap.h | 13 +++++++++++++
>>  mm/memremap.c            |  8 ++++++--
>>  mm/page_alloc.c          | 24 +++++++++++++++++++++++-
>>  3 files changed, 42 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
>> index b46f63dcaed3..bb28d82dda5e 100644
>> --- a/include/linux/memremap.h
>> +++ b/include/linux/memremap.h
>> @@ -114,6 +114,7 @@ struct dev_pagemap {
>>         struct completion done;
>>         enum memory_type type;
>>         unsigned int flags;
>> +       unsigned long align;
> 
> I think this wants some kernel-doc above to indicate that non-zero
> means "use compound pages with tail-page dedup" and zero / PAGE_SIZE
> means "use non-compound base pages". 

Got it. Are you thinking a kernel_doc on top of the variable above, or preferably on top
of pgmap_align()?

> The non-zero value must be
> PAGE_SIZE, PMD_PAGE_SIZE or PUD_PAGE_SIZE. 
> Hmm, maybe it should be an
> enum:
> 
> enum devmap_geometry {
>     DEVMAP_PTE,
>     DEVMAP_PMD,
>     DEVMAP_PUD,
> }
> 
I suppose a converter between devmap_geometry and page_size would be needed too? And maybe
the whole dax/nvdimm align values change meanwhile (as a followup improvement)?

Although to be fair we only ever care about compound page size in this series (and
similarly dax/nvdimm @align properties).

> ...because it's more than just an alignment it's a structural
> definition of how the memmap is laid out.
> 
>>         const struct dev_pagemap_ops *ops;
>>         void *owner;
>>         int nr_range;
>> @@ -130,6 +131,18 @@ static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *pgmap)
>>         return NULL;
>>  }
>>
>> +static inline unsigned long pgmap_align(struct dev_pagemap *pgmap)
>> +{
>> +       if (!pgmap || !pgmap->align)
>> +               return PAGE_SIZE;
>> +       return pgmap->align;
>> +}
>> +
>> +static inline unsigned long pgmap_pfn_align(struct dev_pagemap *pgmap)
>> +{
>> +       return PHYS_PFN(pgmap_align(pgmap));
>> +}
>> +
>>  #ifdef CONFIG_ZONE_DEVICE
>>  bool pfn_zone_device_reserved(unsigned long pfn);
>>  void *memremap_pages(struct dev_pagemap *pgmap, int nid);
>> diff --git a/mm/memremap.c b/mm/memremap.c
>> index 805d761740c4..d160853670c4 100644
>> --- a/mm/memremap.c
>> +++ b/mm/memremap.c
>> @@ -318,8 +318,12 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
>>         memmap_init_zone_device(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
>>                                 PHYS_PFN(range->start),
>>                                 PHYS_PFN(range_len(range)), pgmap);
>> -       percpu_ref_get_many(pgmap->ref, pfn_end(pgmap, range_id)
>> -                       - pfn_first(pgmap, range_id));
>> +       if (pgmap_align(pgmap) > PAGE_SIZE)
>> +               percpu_ref_get_many(pgmap->ref, (pfn_end(pgmap, range_id)
>> +                       - pfn_first(pgmap, range_id)) / pgmap_pfn_align(pgmap));
>> +       else
>> +               percpu_ref_get_many(pgmap->ref, pfn_end(pgmap, range_id)
>> +                               - pfn_first(pgmap, range_id));
>>         return 0;
>>
>>  err_add_memory:
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 58974067bbd4..3a77f9e43f3a 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6285,6 +6285,8 @@ void __ref memmap_init_zone_device(struct zone *zone,
>>         unsigned long pfn, end_pfn = start_pfn + nr_pages;
>>         struct pglist_data *pgdat = zone->zone_pgdat;
>>         struct vmem_altmap *altmap = pgmap_altmap(pgmap);
>> +       unsigned int pfn_align = pgmap_pfn_align(pgmap);
>> +       unsigned int order_align = order_base_2(pfn_align);
>>         unsigned long zone_idx = zone_idx(zone);
>>         unsigned long start = jiffies;
>>         int nid = pgdat->node_id;
>> @@ -6302,10 +6304,30 @@ void __ref memmap_init_zone_device(struct zone *zone,
>>                 nr_pages = end_pfn - start_pfn;
>>         }
>>
>> -       for (pfn = start_pfn; pfn < end_pfn; pfn++) {
>> +       for (pfn = start_pfn; pfn < end_pfn; pfn += pfn_align) {
> 
> pfn_align is in bytes and pfn is in pages... is there a "pfn_align >>=
> PAGE_SHIFT" I missed somewhere?
> 
@pfn_align is in pages too. It's pgmap_align() which is in bytes:

+static inline unsigned long pgmap_pfn_align(struct dev_pagemap *pgmap)
+{
+       return PHYS_PFN(pgmap_align(pgmap));
+}
_______________________________________________
Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
To unsubscribe send an email to linux-nvdimm-leave@lists.01.org