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Re: xfsprogs 2.x vs 3.x logsize changed

To: xfs@xxxxxxxxxxx
Subject: Re: xfsprogs 2.x vs 3.x logsize changed
From: Łukasz Oleś <lukasz.oles@xxxxxxxxxx>
Date: Thu, 18 Nov 2010 10:49:41 +0100
Cc: Eric Sandeen <sandeen@xxxxxxxxxxx>
In-reply-to: <4CE41315.8070402@xxxxxxxxxxx>
Organization: open-e
References: <201011171549.04806.lukasz.oles@xxxxxxxxxx> <4CE41315.8070402@xxxxxxxxxxx>
User-agent: KMail/1.13.5 (Linux/2.6.32-5-686; KDE/4.4.5; i686; ; )
On Wednesday 17 of November 2010 18:38:29 Eric Sandeen wrote:
> On 11/17/10 8:49 AM, Łukasz Oleś wrote:
> > Hi,
> > 
> > I'm upgrading xfsprogs from 2.10.1 to the latest 3.1.4 version. I noticed
> > that when I'm creating large lvm volume (2T) the log size is almost 1G
> > in the old version it was 128M.
> > I know I can manipulate this value with -lsize option, but I'm wondering
> > why this difference is so huge?
> > 
> > On this volume I have one sparse file which is exported by iSCSI Target. 
> > I have script which calculates  for me "seek" value for dd command and
> > now it returns me wrong values.
> > Can I stay with the old log size or maybe there are some good reasons to
> > use new values?
> > 
> > Regards,
> > Łukasz Oleś
> 
> commit a6634fba3dec4a92f0a2c4e30c80b634c0576ad5
> Author: David Chinner <dgc@xxxxxxx>
> Date:   Sun May 10 21:31:22 2009 +0200
> 
>     mkfs: allow to make larger logs
> 
>     Increase the maximum log size supported by mkfs.
> 
>     The log size can be increased easily in mkfs by changing a few
>     defines and a couple of types to allow the log size to increase to
>     just under 2GB. Theoretically, the log size can be made much, much
>     larger than this (up to 2^32 sectors), but going beyond 2^31
>     *bytes* causes integer overflow issues in the kernel log code.
> 
>     We use a maximum size of just under 2GB as exactly 2GB will cause
>     overflow issues on the first transaction reservation.
> 
>     Maximum log size is now reached at a fs size of ~4TB.
> 
>     Signed-off-by: Dave Chinner <dgc@xxxxxxx>
>     Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> 
> 
> did:
> 
> @@ -1737,10 +1737,10 @@ _("size %s specified for log subvolume is too
> large, maximum is %lld blocks\n"), logblocks = 0;
>         } else if (loginternal && !logsize) {
>                 /*
> -                * logblocks grows from min_logblocks to XFS_MAX_LOG_BLOCKS
> -                * at 128GB
> -                *
> -                * 2048 = 128GB / MAX_LOG_BYTES
> +                * With a 2GB max log size, default to maximum size
> +                * at 4TB. This keeps the same ratio from the older
> +                * max log size of 128M at 256GB fs size. IOWs,
> +                * the ratio of fs size to log size is 2048:1.
>                  */
>                 logblocks = (dblocks << blocklog) / 2048;
>                 logblocks = logblocks >> blocklog;
> 
> old MAX was:
> 
> -#define XFS_MAX_LOG_BYTES      (128 * 1024 * 1024)
> 
> In your case ... I'm not sure a larger log is going to help, I think
> keeping it smaller is fine if you wish.
> 
> Dave may have a different opinion though :)
> 
> -Eric

Ok, so it's this commit http://git.kernel.org/?p=fs/xfs/xfsprogs-
dev.git;a=commitdiff;h=a6634fba3dec4a92f0a2c4e30c80b634c0576ad5

Would it be safe if I just revert this commit?  It looks safe for me, but 
maybe other things depends on it and I will break something.

Regards,
Łukasz Oleś

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