linux-kernel - Re: [PATCH] fs: buffer: Modify alloc_page

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Date:   Fri, 23 Jun 2017 16:26:25 +0800
From:   Sean Fu <fxinrong@...il.com>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     shli@...nel.org, anton@...era.com, jack@...e.cz, axboe@...com,
        ebiggers@...gle.com, rpeterso@...hat.com, bmarzins@...hat.com,
        linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-ntfs-dev@...ts.sourceforge.net
Subject: Re: [PATCH] fs: buffer: Modify alloc_page_buffers.

On Mon, Jun 19, 2017 at 05:03:16PM +0100, Al Viro wrote:
> On Mon, Jun 19, 2017 at 09:01:36PM +0800, Sean Fu wrote:
> > Make alloc_page_buffers support circular buffer list and initialise
> > b_state field.
> > Optimize the performance by removing the buffer list traversal to create
> > circular buffer list.
> 
> > -		bh = head = alloc_page_buffers(page, blocksize, 1);
> > +		bh = head = alloc_page_buffers(page, blocksize, 1, 0, 0);
> 
> Frankly, I don't like that change of calling conventions; it's very easy to
> mess the order of arguments when using interfaces like that and it's hell
> to find when trying to debug the resulting mess.
> 
> Do you really get an observable change in performance?  What loads are
> triggering it?
Sorry for my mistake.
Infact, The time of writting a large file depends on saveral other
factors, eg system workload.
Yesterday, I tried to test the time of single calling create_empty_buffers by kretprobe
and found that the performance difference is too small to measure it.

before:
[  944.632027] create_empty_buffers returned 878736736 and took 2160 ns
to execute
[  944.632286] create_empty_buffers returned 878962832 and took 451 ns
to execute
[  944.632302] create_empty_buffers returned 878962016 and took 226 ns
to execute
[  944.632728] create_empty_buffers returned 878962832 and took 235 ns
to execute
[  944.633105] create_empty_buffers returned 878962832 and took 167 ns
to execute
[  944.633421] create_empty_buffers returned 878962832 and took 160 ns
to execute

after:
[39209.076519] create_empty_buffers returned 383804768 and took 1666 ns
to execute
[39209.077032] create_empty_buffers returned 383804768 and took 366 ns
to execute
[39209.077120] create_empty_buffers returned 558412336 and took 179 ns
to execute
[39209.077127] create_empty_buffers returned 558413152 and took 148 ns
to execute
[39209.077525] create_empty_buffers returned 558412336 and took 201 ns
to execute
[39209.078255] create_empty_buffers returned 814328768 and took 880 ns
to execute
[39209.078498] create_empty_buffers returned 558412336 and took 564 ns
to execute
[39209.078737] create_empty_buffers returned 558413152 and took 196 ns
to execute

This patch also complicates code.
Please ignore it.
Thanks all of you.