Re: [RFC v2 PATCH 03/17] mm: Introduce try_vma_alloc_movable_folio()

Ryan Roberts
2023-04-17T10:12:38Z

On 17/04/2023 09:49, Yin, Fengwei wrote:
>
>
> On 4/14/2023 9:02 PM, Ryan Roberts wrote:
>> Opportunistically attempt to allocate high-order folios in highmem,
>> optionally zeroed. Retry with lower orders all the way to order-0, until
>> success. Although, of note, order-1 allocations are skipped since a
>> large folio must be at least order-2 to work with the THP machinery. The
>> user must check what they got with folio_order().
>>
>> This will be used to oportunistically allocate large folios for
>> anonymous memory with a sensible fallback under memory pressure.
>>
>> For attempts to allocate non-0 orders, we set __GFP_NORETRY to prevent
>> high latency due to reclaim, instead preferring to just try for a lower
>> order. The same approach is used by the readahead code when allocating
>> large folios.
> I am not sure whether anonymous page can share the same approach as page
> cache. The latency of new page cache is dominated by IO. So it may be not
> big deal to retry with different order some times.
>
> Retry too many times could bring latency for anonymous page allocation.

Perhaps I'm better off just using vma_thp_gfp_mask(), or at least taking
inspiration from it?

>
> Regards
> Yin, Fengwei
>
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> ---
>> mm/memory.c | 33 +++++++++++++++++++++++++++++++++
>> 1 file changed, 33 insertions(+)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 9d5e8be49f3b..ca32f59acef2 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -2989,6 +2989,39 @@ static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
>> return 0;
>> }
>>
>> +static inline struct folio *vma_alloc_movable_folio(struct vm_area_struct *vma,
>> + unsigned long vaddr, int order, bool zeroed)
>> +{
>> + gfp_t gfp = order > 0 ? __GFP_NORETRY | __GFP_NOWARN : 0;
>> +
>> + if (zeroed)
>> + return vma_alloc_zeroed_movable_folio(vma, vaddr, gfp, order);
>> + else
>> + return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp, order, vma,
>> + vaddr, false);
>> +}
>> +
>> +/*
>> + * Opportunistically attempt to allocate high-order folios, retrying with lower
>> + * orders all the way to order-0, until success. order-1 allocations are skipped
>> + * since a folio must be at least order-2 to work with the THP machinery. The
>> + * user must check what they got with folio_order(). vaddr can be any virtual
>> + * address that will be mapped by the allocated folio.
>> + */
>> +static struct folio *try_vma_alloc_movable_folio(struct vm_area_struct *vma,
>> + unsigned long vaddr, int order, bool zeroed)
>> +{
>> + struct folio *folio;
>> +
>> + for (; order > 1; order--) {
>> + folio = vma_alloc_movable_folio(vma, vaddr, order, zeroed);
>> + if (folio)
>> + return folio;
>> + }
>> +
>> + return vma_alloc_movable_folio(vma, vaddr, 0, zeroed);
>> +}
>> +
>> /*
>> * Handle write page faults for pages that can be reused in the current vma
>> *
>> --
>> 2.25.1
>>