Re: [RFC PATCH 0/6] Do not call ->writepage[s] from direct reclaim and use a_ops->writepages() where possible

Nick Piggin
2010-06-16T07:57:31Z

On Tue, Jun 15, 2010 at 03:13:09PM -0400, Rik van Riel wrote:
> On 06/15/2010 12:54 PM, Christoph Hellwig wrote:
> >On Tue, Jun 15, 2010 at 12:49:49PM -0400, Rik van Riel wrote:
> >>This is already in a filesystem. Why does ->writepage get
> >>called a second time? Shouldn't this have a gfp_mask
> >>without __GFP_FS set?
> >
> >Why would it? GFP_NOFS is not for all filesystem code, but only for
> >code where we can't re-enter the filesystem due to deadlock potential.
>
> Why? How about because you know the stack is not big enough
> to have the XFS call path on it twice? :)
>
> Isn't the whole purpose of this patch series to prevent writepage
> from being called by the VM, when invoked from a deep callstack
> like xfs writepage?
>
> That sounds a lot like simply wanting to not have GFP_FS...

buffered write path uses __GFP_FS by design because huge amounts
of (dirty) memory can be allocated in doing pagecache writes. If
would be nasty if that was not allowed to wait for filesystem
activity.