linux-kernel - Re: [PATCH v2] x86: enable RCU based table free

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Message-ID: <87o9r4qg09.fsf@vitty.brq.redhat.com>
Date:   Fri, 25 Aug 2017 09:10:46 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jork Loeser <Jork.Loeser@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v2] x86: enable RCU based table free

Vitaly Kuznetsov <vkuznets@...hat.com> writes:

> Peter Zijlstra <peterz@...radead.org> writes:
>
>> On Thu, Aug 24, 2017 at 11:22:58AM +0200, Vitaly Kuznetsov wrote:
>>
>>> diff --git a/arch/x86/include/asm/tlb.h b/arch/x86/include/asm/tlb.h
>>> index c7797307fc2b..d43a7fcafee9 100644
>>> --- a/arch/x86/include/asm/tlb.h
>>> +++ b/arch/x86/include/asm/tlb.h
>>> @@ -15,4 +15,9 @@
>>>  
>>>  #include <asm-generic/tlb.h>
>>>  
>>> +static inline void __tlb_remove_table(void *table)
>>> +{
>>> +	free_page_and_swap_cache(table);
>>> +}
>>
>> Most other archs have this in pgtable.h, only ARM* has it in tlb.h.
>>
>
> Sure, I can move it in v3 if nobody objects.
>

Well, turns out it is going to be a bit tricky. 

free_page_and_swap_cache() is defined in linux/swap.h but we can't just
include it from arch/x86/include/asm/pgtable.h as pgtable.h itself is
included from swap.h:

...
In file included from ./include/linux/mm.h:70:0,
                 from ./include/linux/memcontrol.h:29,
                 from ./include/linux/swap.h:8,
                 from ./include/linux/suspend.h:4,
                 from arch/x86/kernel/asm-offsets.c:12:
./arch/x86/include/asm/pgtable.h: In function ‘__tlb_remove_table’:
./arch/x86/include/asm/pgtable.h:1252:2: error: implicit declaration of function ‘free_page_and_swap_cache’; did you mean ‘file_write_and_wait_range’? [-Werror=implicit-function-declaration]
  free_page_and_swap_cache(table);
  ^~~~~~~~~~~~~~~~~~~~~~~~
...

An easy solution would be to make __tlb_remove_table() a define instead
of inline but personally I'd rather prefer to follow ARM and leave it in
tlb.h.

-- 
  Vitaly