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

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Message-ID: <fac5a6f4-3dda-2ec4-81ec-4a4a7ad2a571@microsoft.com>
Date:   Wed, 12 Sep 2018 17:46:53 +0000
From:   Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>
CC:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 3/4] mm: Defer ZONE_DEVICE page initialization to the
 point where we init pgmap



On 9/12/18 12:50 PM, Dan Williams wrote:
> On Wed, Sep 12, 2018 at 8:48 AM, Alexander Duyck
> <alexander.duyck@...il.com> wrote:
>> On Wed, Sep 12, 2018 at 6:59 AM Pasha Tatashin
>> <Pavel.Tatashin@...rosoft.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