linux-kernel - Re: [PATCH v3] introduce sys_syncfs to sync a single file system

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Date:	Fri, 11 Mar 2011 19:40:30 -0500
From:	Ric Wheeler <ricwheeler@...il.com>
To:	Indan Zupancic <indan@....nu>
CC:	Arnd Bergmann <arnd@...db.de>, Sage Weil <sage@...dream.net>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Jonathan Nieder <jrnieder@...il.com>,
	akpm@...ux-foundation.org, linux-api@...r.kernel.org,
	mtk.manpages@...il.com, viro@...iv.linux.org.uk, hch@....de,
	l@...per.es
Subject: Re: [PATCH v3] introduce sys_syncfs to sync a single file system

On 03/11/2011 06:45 PM, Indan Zupancic wrote:
> On Fri, March 11, 2011 12:55, Arnd Bergmann wrote:
>> On Friday 11 March 2011, Indan Zupancic wrote:
>>>>        http://marc.info/?l=linux-fsdevel&amp;m=127970513829285&amp;w=2
>>> The patch there seems much more reasonable than introducing a whole
>>> new systemcall just for 20 lines of kernel code. New system calls are
>>> added too easily nowadays.
>> The only problem with adding new system calls is that we are stuck
>> with the interface until the end of time, so we must be sure not
>> to get it wrong. The same thing is true for any other interface
>> such as ioctl or extensions to existing system calls. People usually
>> get away with adding new ioctls more easily because it is less
>> obvious when they are added.
> Agreed.
>
> I'm not sure this feature is important enough to add. I can't really
> think of a regular use case where this would be useful, generally
> it's transparent on which mount files are. Add symlinks, and you
> give users a lot of rope. Any user has to make sure that all the
> files they want to sync are on the same file system.
>
> About the arguments against sync(2):
>
>>   - On machines with many mounts, it is not at all uncommon for some of
>>     them to hang (e.g. unresponsive NFS server).  sync(2) will get stuck on
>>     those and may never get to the one you do care about (e.g., /).
> It would be better to fix NFS, or mount it with the fsc option (assuming
> a sync will write to the local cache instead of hanging forever then).
>
>>   - Some applications write lots of data to the file system and then
>>     want to make sure it is flushed to disk.  Calling fsync(2) on each
>>     file introduces unnecessary ordering constraints that result in a large
>>     amount of sub-optimal writeback/flush/commit behavior by the file
>>     system.
> You can use sync_file_range() on those files to schedule the writes
> and then do the fsync(2) as usual (both on files and dirs).
>
> If there still is a good reason to implement this, please don't add it
> as a new system call, but add it to sync_file_range(), as that seems
> the best place for odd file synchronisation operations.
>
> Greetings,
>
> Indan
>
>
> --

Hi Indan,

I think that you missed the point of the extension.

Ric

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