All of lore.kernel.org
 help / color / mirror / Atom feed
From: Matthew Wilcox <matthew@wil.cx>
To: Stephen Frost <sfrost@snowman.net>
Cc: Benjamin LaHaise <bcrl@kvack.org>,
	Andres Freund <andres@anarazel.de>,
	Andi Kleen <andi@firstfloor.org>,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, robertmhaas@gmail.com,
	pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Improve lseek scalability v3
Date: Mon, 19 Sep 2011 07:25:00 -0600	[thread overview]
Message-ID: <20110919132500.GA16740@parisc-linux.org> (raw)
In-Reply-To: <20110919123100.GJ12765@tamriel.snowman.net>

On Mon, Sep 19, 2011 at 08:31:00AM -0400, Stephen Frost wrote:
> * Benjamin LaHaise (bcrl@kvack.org) wrote:
> > For such tables, can't Postgres track the size of the file internally?  I'm 
> > assuming it's keeping file descriptors open on the tables it manages, in 
> > which case when it writes to a file to extend it, the internally stored size 
> > could be updated.  Not making a syscall at all would scale far better than 
> > even a modified lseek() will perform.
> 
> We'd have to have it in shared memory and have a lock around it, it
> wouldn't be cheap at all.

Yep, that makes perfect sense.  After all, the kernel does basically the
same thing to maintain this information; why should we have userspace
duplicating the same infrastructure?

I must admit, I'd never heard of this usage of lseek to get the current
size of a file before; I'd assumed everybody used fstat.  Given this
legitimate reason for a high-frequency calling of lseek, I withdraw my
earlier objection to the patch series.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

  reply	other threads:[~2011-09-19 13:25 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-15 23:06 Improve lseek scalability v3 Andi Kleen
2011-09-15 23:06 ` [PATCH 1/7] BTRFS: Fix lseek return value for error Andi Kleen
2011-09-15 23:47   ` Thomas Gleixner
2011-09-16 15:48   ` Christoph Hellwig
2011-09-16 16:38     ` Andi Kleen
2011-09-17  6:10     ` Jeff Liu
2011-09-17 23:03       ` Andreas Dilger
2011-09-18  1:46         ` Andi Kleen
2011-09-18  7:29           ` Jeff Liu
2011-09-18  8:42             ` Marco Stornelli
2011-09-18 10:33               ` Jeff liu
2011-09-18 10:33                 ` Jeff liu
2011-09-18 14:55                 ` Chris Mason
2011-09-18 14:55                   ` Chris Mason
2011-09-18 14:55                   ` Chris Mason
2011-09-19 17:52                   ` Andi Kleen
2011-09-19 19:30                     ` Chris Mason
2011-09-19 19:59                       ` Andi Kleen
2011-09-19 22:55                         ` Chris Mason
2011-09-15 23:06 ` [PATCH 2/7] VFS: Do (nearly) lockless generic_file_llseek Andi Kleen
2011-09-15 23:06 ` [PATCH 3/7] VFS: Make generic lseek lockless safe Andi Kleen
2011-09-15 23:06 ` [PATCH 4/7] VFS: Add generic_file_llseek_size Andi Kleen
2011-09-16 15:50   ` Christoph Hellwig
2011-09-15 23:06 ` [PATCH 5/7] LSEEK: EXT4: Replace cut'n'pasted llseek code with generic_file_llseek_size Andi Kleen
2011-09-15 23:06 ` [PATCH 6/7] LSEEK: NFS: Drop unnecessary locking in llseek Andi Kleen
2011-09-15 23:06 ` [PATCH 7/7] LSEEK: BTRFS: Avoid i_mutex for SEEK_{CUR,SET,END} Andi Kleen
2011-09-16 13:00 ` Improve lseek scalability v3 Matthew Wilcox
2011-09-16 13:19   ` Josef Bacik
2011-09-16 14:16   ` Andres Freund
2011-09-16 14:23     ` Andi Kleen
2011-09-16 14:41       ` Andres Freund
2011-09-16 15:36     ` Matthew Wilcox
2011-09-16 17:27       ` Andres Freund
2011-09-16 17:39         ` [HACKERS] " Alvaro Herrera
2011-09-16 17:39           ` Alvaro Herrera
2011-09-16 17:50           ` [HACKERS] " Andi Kleen
2011-09-16 20:08         ` Benjamin LaHaise
2011-09-16 21:02           ` Andres Freund
2011-09-16 21:05             ` [HACKERS] " Andres Freund
2011-09-16 22:44           ` Greg Stark
2011-09-19 12:31           ` [HACKERS] " Stephen Frost
2011-09-19 12:31             ` Stephen Frost
2011-09-19 13:25             ` Matthew Wilcox [this message]
2011-09-20  7:18               ` [HACKERS] " Marco Stornelli
2011-09-20  7:18                 ` Marco Stornelli
2011-09-19 13:30             ` Robert Haas
2011-09-16 14:26   ` Andres Freund
2011-10-01 20:46 ` Andres Freund
2011-10-01 20:49   ` [PATCH 1/2] LSEEK: BTRFS: Avoid i_mutex for SEEK_{CUR,SET,END} Andres Freund
2011-11-02  8:29     ` Christoph Hellwig
2011-11-05 15:27       ` Chris Mason
2012-03-07 17:16         ` Andres Freund
2011-10-01 20:50   ` [PATCH 2/2] btrfs: Don't have multiple paths to error out in btrfs_file_llseek Andres Freund
2011-10-02  5:28   ` Improve lseek scalability v3 Andi Kleen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20110919132500.GA16740@parisc-linux.org \
    --to=matthew@wil.cx \
    --cc=andi@firstfloor.org \
    --cc=andres@anarazel.de \
    --cc=bcrl@kvack.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=pgsql-hackers@postgresql.org \
    --cc=robertmhaas@gmail.com \
    --cc=sfrost@snowman.net \
    --cc=viro@zeniv.linux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.