Re: [PATCH v3 2/4] mm: Default implementation of arch_wants_pte_order()

From: Yu Zhao <yuzhao@google.com>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Yin Fengwei <fengwei.yin@intel.com>,
	 David Hildenbrand <david@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	 Will Deacon <will@kernel.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	 Yang Shi <shy828301@gmail.com>,
	"Huang, Ying" <ying.huang@intel.com>, Zi Yan <ziy@nvidia.com>,
	 Luis Chamberlain <mcgrof@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	 linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 2/4] mm: Default implementation of arch_wants_pte_order()
Date: Fri, 14 Jul 2023 10:54:20 -0600	[thread overview]
Message-ID: <CAOUHufZ7HJZW8Srwatyudf=FbwTGQtyq4DyL2SHwSg37N_Bo_A@mail.gmail.com> (raw)
In-Reply-To: <20230714161733.4144503-2-ryan.roberts@arm.com>

On Fri, Jul 14, 2023 at 10:17 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> arch_wants_pte_order() can be overridden by the arch to return the
> preferred folio order for pte-mapped memory. This is useful as some
> architectures (e.g. arm64) can coalesce TLB entries when the physical
> memory is suitably contiguous.
>
> The first user for this hint will be FLEXIBLE_THP, which aims to
> allocate large folios for anonymous memory to reduce page faults and
> other per-page operation costs.
>
> Here we add the default implementation of the function, used when the
> architecture does not define it, which returns -1, implying that the HW
> has no preference. In this case, mm will choose it's own default order.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Reviewed-by: Yu Zhao <yuzhao@google.com>

Thanks: -1 actually is better than 0 (what I suggested) for the obvious reason.