From: Fengguang Wu <fengguang.wu@intel.com>
To: Ni zhan Chen <nizhan.chen@gmail.com>
Cc: Dave Chinner <david@fromorbit.com>,
YingHang Zhu <casualfisher@gmail.com>,
akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state
Date: Fri, 26 Oct 2012 16:02:40 +0800 [thread overview]
Message-ID: <20121026080240.GA13662@localhost> (raw)
In-Reply-To: <508A4007.5080906@gmail.com>
On Fri, Oct 26, 2012 at 03:47:19PM +0800, Ni zhan Chen wrote:
> On 10/26/2012 03:36 PM, Fengguang Wu wrote:
> >On Fri, Oct 26, 2012 at 03:19:57PM +0800, Ni zhan Chen wrote:
> >>On 10/26/2012 03:09 PM, Fengguang Wu wrote:
> >>>On Fri, Oct 26, 2012 at 03:03:12PM +0800, Ni zhan Chen wrote:
> >>>>On 10/26/2012 02:58 PM, Fengguang Wu wrote:
> >>>>>> static void shrink_readahead_size_eio(struct file *filp,
> >>>>>> struct file_ra_state *ra)
> >>>>>> {
> >>>>>>- ra->ra_pages /= 4;
> >>>>>>+ spin_lock(&filp->f_lock);
> >>>>>>+ filp->f_mode |= FMODE_RANDOM;
> >>>>>>+ spin_unlock(&filp->f_lock);
> >>>>>>
> >>>>>>As the example in comment above this function, the read maybe still
> >>>>>>sequential, and it will waste IO bandwith if modify to FMODE_RANDOM
> >>>>>>directly.
> >>>>>Yes immediately disabling readahead may hurt IO performance, the
> >>>>>original '/ 4' may perform better when there are only 1-3 IO errors
> >>>>>encountered.
> >>>>Hi Fengguang,
> >>>>
> >>>>Why the number should be 1-3?
> >>>The original behavior is '/= 4' on each error.
> >>>
> >>>After 1 errors, readahead size will be shrinked by 1/4
> >>>After 2 errors, readahead size will be shrinked by 1/16
> >>>After 3 errors, readahead size will be shrinked by 1/64
> >>>After 4 errors, readahead size will be effectively 0 (disabled)
> >>But from function shrink_readahead_size_eio and its caller
> >>filemap_fault I can't find the behavior you mentioned. How you
> >>figure out it?
> >It's this line in shrink_readahead_size_eio():
> >
> > ra->ra_pages /= 4;
>
> Yeah, I mean why the 4th readahead size will be 0(disabled)? What's
> the original value of ra->ra_pages? How can guarantee the 4th shrink
> readahead size can be 0?
Ah OK, I'm talking about the typical case. The default readahead size
is 128k, which will become 0 after / 256. The reasonable good ra size
for hard disks is 1MB=256pages, which also becomes 1page after 4 errors.
Thanks,
Fengguang
next prev parent reply other threads:[~2012-10-26 8:02 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-23 12:46 [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state Ying Zhu
2012-10-23 13:21 ` Ni zhan Chen
[not found] ` <CAA9v8mGMa3SDD1OLTG_wdhCGx7K-0kvSV1+MRi9uCGTz6zZaLg@mail.gmail.com>
2012-10-23 13:41 ` YingHang Zhu
2012-10-24 1:02 ` Ni zhan Chen
2012-10-24 1:33 ` YingHang Zhu
2012-10-23 22:47 ` Dave Chinner
2012-10-23 23:53 ` YingHang Zhu
2012-10-24 20:19 ` Dave Chinner
2012-10-25 0:17 ` YingHang Zhu
2012-10-25 1:48 ` Ni zhan Chen
2012-10-25 1:50 ` Dave Chinner
2012-10-25 2:04 ` YingHang Zhu
2012-10-25 2:12 ` Ni zhan Chen
2012-10-25 2:31 ` YingHang Zhu
2012-10-25 2:58 ` Fengguang Wu
2012-10-25 3:12 ` YingHang Zhu
2012-10-26 0:25 ` Dave Chinner
2012-10-26 1:27 ` Fengguang Wu
2012-10-26 2:30 ` Ni zhan Chen
2012-10-26 3:28 ` YingHang Zhu
2012-10-26 3:51 ` Ni zhan Chen
2012-10-26 4:35 ` YingHang Zhu
2012-10-26 6:58 ` Fengguang Wu
2012-10-26 7:03 ` Ni zhan Chen
2012-10-26 7:09 ` Fengguang Wu
2012-10-26 7:19 ` Ni zhan Chen
2012-10-26 7:36 ` Fengguang Wu
2012-10-26 7:47 ` Ni zhan Chen
2012-10-26 8:02 ` Fengguang Wu [this message]
2012-10-26 8:08 ` Ni zhan Chen
2012-10-26 8:13 ` YingHang Zhu
2012-10-26 2:25 ` Ni zhan Chen
2012-10-26 3:38 ` YingHang Zhu
2012-10-26 3:55 ` Fengguang Wu
2012-10-26 5:00 ` YingHang Zhu
2012-10-25 2:38 ` Fengguang Wu
2012-10-25 3:08 ` YingHang Zhu
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