mm: alloc_anon_folio: avoid doing vma_thp_gfp_mask in fallback cases

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.

Link: https://lkml.kernel.org/r/20240329073750.20012-1-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory.c

@@ -4358,6 +4358,9 @@ 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) {