linux-kernel - Re: [PATCH 2/2] mm: make do

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Date:	Fri, 3 Feb 2012 19:41:07 +0530
From:	Amit Sahrawat <amit.sahrawat83@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: make do_writepages() use plugging

Is there a case for introducing blk_plug in write_one_page() can't
seem to find that support in the code flow
write_one_page()->mpage_writepage()

Regards,
Amit Sahrawat


On Fri, Feb 3, 2012 at 7:31 PM, Amit Sahrawat <amit.sahrawat83@...il.com> wrote:
> Hi Peter,
> Thanks for pointing out.
>
> While checking the plug support in Write code flow, I came across this
> main point from which - we invoke
> writepages(mapping->a_ops->writepages(mapping, wbc)) from almost all
> the the filesystems.
>
> By mistake I checked 2 different kernel versions for this code(and
> missed that the current version already has put plug in
> mpage_writepages) ... so may be this patch is not worth considering.
>
> Regards,
> Amit Sahrawat
>
>
> On Fri, Feb 3, 2012 at 7:02 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>> On Fri, 2012-02-03 at 18:57 +0530, Amit Sahrawat wrote:
>>> This will cover all the invocations for writepages to be called with
>>> plugging support.
>>
>> This changelog fails to explain why this is a good thing... I thought
>> the idea of the new plugging stuff was that we now don't need to
>> sprinkle plugs all over the kernel..
>>
>>> Signed-off-by: Amit Sahrawat <a.sahrawat@...sung.com>
>>> ---
>>>  mm/page-writeback.c |    4 ++++
>>>  1 files changed, 4 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>>> index 363ba70..2bea32c 100644
>>> --- a/mm/page-writeback.c
>>> +++ b/mm/page-writeback.c
>>> @@ -1866,14 +1866,18 @@ EXPORT_SYMBOL(generic_writepages);
>>>
>>>  int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
>>>  {
>>> +     struct blk_plug plug;
>>>       int ret;
>>>
>>>       if (wbc->nr_to_write <= 0)
>>>               return 0;
>>> +
>>> +     blk_start_plug(&plug);
>>>       if (mapping->a_ops->writepages)
>>>               ret = mapping->a_ops->writepages(mapping, wbc);
>>>       else
>>>               ret = generic_writepages(mapping, wbc);
>>> +     blk_finish_plug(&plug);
>>>       return ret;
>>>  }
>>>
>>
>>
>>
--
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