Re: [PATCH] mm: alloc_anon_folio: avoid doing vma_thp_gfp_mask in fallback cases

[Ryan Roberts <ryan.roberts@arm.com>]

On 29/03/2024 07:37, Barry Song wrote:
> From: Barry Song <v-songbaohua@oppo.com>
> 
> Fallback rates surpassing 90% have been observed on phones utilizing 64KiB
> CONT-PTE mTHP. In these scenarios, when one out of every 16 PTEs fails
> to allocate large folios, the remaining 15 PTEs fallback. Consequently,
> invoking vma_thp_gfp_mask seems redundant in such cases. Furthermore,
> abstaining from its use can also contribute to improved code readability.
> 
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Alistair Popple <apopple@nvidia.com>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: "Huang, Ying" <ying.huang@intel.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Itaru Kitayama <itaru.kitayama@gmail.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Luis Chamberlain <mcgrof@kernel.org>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Yin Fengwei <fengwei.yin@intel.com>
> Cc: Yu Zhao <yuzhao@google.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>

> ---
>  mm/memory.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index c9c1031c2ecb..010e7bb20d2b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4353,6 +4353,9 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
>  
>  	pte_unmap(pte);
>  
> +	if (!orders)
> +		goto fallback;
> +
>  	/* Try allocating the highest of the remaining orders. */
>  	gfp = vma_thp_gfp_mask(vma);
>  	while (orders) {