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Re: posix_fallocate

To: xfs@xxxxxxxxxxx
Subject: Re: posix_fallocate
From: Krzysztof Błaszkowski <kb@xxxxxxxxxxxxxxx>
Date: Mon, 10 May 2010 20:17:11 +0200
Cc: Eric Sandeen <sandeen@xxxxxxxxxxx>
In-reply-to: <4BE81AB4.7000600@xxxxxxxxxxx>
Organization: Systemy mikroprocesorowe
References: <201005071022.37863.kb@xxxxxxxxxxxxxxx> <201005100911.52491.kb@xxxxxxxxxxxxxxx> <4BE81AB4.7000600@xxxxxxxxxxx>
User-agent: KMail/1.9.5
On Monday 10 May 2010 16:39, Eric Sandeen wrote:
> Krzysztof Błaszkowski wrote:
> > On Friday 07 May 2010 18:53, Eric Sandeen wrote:
> >> Eric Sandeen wrote:
> >>> Krzysztof Błaszkowski wrote:
> >>>> Hello,
> >>>>
> >>>> I use this to preallocate large space but found an issue.
> >>>> Posix_fallocate works right with sizes like 100G, 1T and even 10T on
> >>>> some boxes (on some other can fail after e.g. 7T threshold) but if i
> >>>> tried e.g. 16T the user space process would be "R"unning forever and
> >>>> it is not interruptible. Furthermore some other not related processes
> >>>> like sshd, bash enter D state. There is nothing in kernel log.
> >>
> >> Oh, one thing you should know is that depending on your version of
> >> glibc, posix_fallocate may be writing 0s and not using preallocation
> >> calls.
> >
> > I am absolutely sure that recent libc doesn't emulate this syscall
>
> right, recent glibc does not (unless the underlying fs doesn't support it)
>
> ...
>
> > We stick with 2.6.31.5 which seems to be good for us. We do not change
> > kernels easily, as soon as higher revision arrives because it doesn't
> > make sense from stability point of view. We have seen too many times
> > regression bugs so if we are confident with some revision then there is
> > no point to change this.
>
> It was just a testing suggestion, but I already tested upstream and the
> problem persists, now just need to find the time to dig into it.

I see and I am glad you confirmed this. Do you think that fallocate called 
many times with fixed size and increasing offset will work better than one 
time call with huge size @ 0 offset ?

Krzysztof
>
> -Eric
>
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