Re: [PATCH 3/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap

From: Pasha Tatashin <Pavel.Tatashin@microsoft.com>
To: Dan Williams <dan.j.williams@intel.com>,
	Alexander Duyck <alexander.duyck@gmail.com>
Cc: linux-mm <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	"Michal Hocko" <mhocko@suse.com>,
	"Dave Jiang" <dave.jiang@intel.com>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Dave Hansen" <dave.hansen@intel.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Logan Gunthorpe" <logang@deltatee.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH 3/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap
Date: Wed, 12 Sep 2018 17:46:53 +0000	[thread overview]
Message-ID: <fac5a6f4-3dda-2ec4-81ec-4a4a7ad2a571@microsoft.com> (raw)
In-Reply-To: <CAPcyv4gEDwp8Xh4_E8RNBC_OqstwhqxkZOpvYjWd_siB4C=BEQ@mail.gmail.com>

On 9/12/18 12:50 PM, Dan Williams wrote:
> On Wed, Sep 12, 2018 at 8:48 AM, Alexander Duyck
> <alexander.duyck@gmail.com> wrote:
>> On Wed, Sep 12, 2018 at 6:59 AM Pasha Tatashin
>> <Pavel.Tatashin@microsoft.com> wrote:
>>>
>>> Hi Alex,
>>
>> Hi Pavel,
>>
>>> Please re-base on linux-next,  memmap_init_zone() has been updated there
>>> compared to mainline. You might even find a way to unify some parts of
>>> memmap_init_zone and memmap_init_zone_device as memmap_init_zone() is a
>>> lot simpler now.
>>
>> This patch applied to the linux-next tree with only a little bit of
>> fuzz. It looks like it is mostly due to some code you had added above
>> the function as well. I have updated this patch so that it will apply
>> to both linux and linux-next by just moving the new function to
>> underneath memmap_init_zone instead of above it.
>>
>>> I think __init_single_page() should stay local to page_alloc.c to keep
>>> the inlining optimization.
>>
>> I agree. In addition it will make pulling common init together into
>> one space easier. I would rather not have us create an opportunity for
>> things to further diverge by making it available for anybody to use.
> 
> I'll buy the inline argument for keeping the new routine in
> page_alloc.c, but I otherwise do not see the divergence danger or
> "making __init_single_page() available for anybody" given the the
> declaration is limited in scope to a mm/ local header file.
> 

Hi Dan,

It is much harder for compiler to decide that function can be inlined
once it is non-static. Of course, we can simply move this function to a
header file, and declare it inline to begin with.

But, still __init_single_page() is so performance sensitive, that I'd
like to reduce number of callers to this function, and keep it in .c file.

Thank you,
Pavel