linux-ext4 - Re: ENOSPC returned during writepages

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Message-Id: <1219339027.6342.19.camel@mingming-laptop>
Date:	Thu, 21 Aug 2008 10:17:07 -0700
From:	Mingming Cao <cmm@...ibm.com>
To:	Theodore Tso <tytso@....edu>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: ENOSPC returned during writepages


在 2008-08-21四的 11:35 -0400，Theodore Tso写道：
> On Thu, Aug 21, 2008 at 08:48:15PM +0530, Aneesh Kumar K.V wrote:
> > > I have a feeling that we did not try very hard before invalidate the
> > > dirty page which fail to map to disks. Perhaps we should try a few more
> > > times before give up. Also in that case, perhaps we should turn off
> > > delalloc fs wide, so the new writers won't take the subsequently made
> > > avaible free blocks away from this unlucky delalloc da writepages.
> > 
> > How do we try hard ? The mballoc already try had to allocate blocks. So I
> > am not sure what do we achieve by requesting for block allocation again.
> 
> So here's the problem that we face.  If we have a situation where the
> disk fills temporarily, but then subsequently space gets freed up, it
> would be preferable if the dirty page isn't invalidated, and so
> periodically (or perhaps via "there's-free-space-now notifier") we
> retry the delayed allocation so we don't lose data during a transient
> disk full situation.  But at the same time, we don't want an fsync()
> on the entire filesystem, or a umount on the filesystem, to hang
> forever.
> 

This situation (disk fills temporarily) is not new, we handled this in
ext4_write_begin() (and other places)  by retry allocation three times
in case of ENOSPC error. we could do the same retry  in
ext4_da_writepages().

Mingming
> 						- Ted
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