Date:   Wed, 26 Jul 2023 06:26:23 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Eric Van Hensbergen <ericvh@...nel.org>,
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Subject: Re: [PATCH v6 3/7] tmpfs: bump the mtime/ctime/iversion when page
 becomes writeable

On Tue, 2023-07-25 at 18:39 -0700, Hugh Dickins wrote:
> On Tue, 25 Jul 2023, Jeff Layton wrote:
> 
> > Most filesystems that use the pagecache will update the mtime, ctime,
> > and change attribute when a page becomes writeable. Add a page_mkwrite
> > operation for tmpfs and just use it to bump the mtime, ctime and change
> > attribute.
> > 
> > This fixes xfstest generic/080 on tmpfs.
> 
> Huh.  I didn't notice when this one crept into the multigrain series.
> 
> I'm inclined to NAK this patch: at the very least, it does not belong
> in the series, but should be discussed separately.
> 
> Yes, tmpfs does not and never has used page_mkwrite, and gains some
> performance advantage from that.  Nobody has ever asked for this
> change before, or not that I recall.
> 
> Please drop it from the series: and if you feel strongly, or know
> strong reasons why tmpfs suddenly needs to use page_mkwrite now,
> please argue them separately.  To pass generic/080 is not enough.
> 
> Thanks,
> Hugh
> 

Dropped.

This was just something I noticed while testing this series. It stood
out since I was particularly watching for timestamp-related test
failures. I don't feel terribly strongly about it.

Thanks!

> > 
> > Signed-off-by: Jeff Layton <jlayton@...nel.org>
> > ---
> >  mm/shmem.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index b154af49d2df..654d9a585820 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -2169,6 +2169,16 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
> >  	return ret;
> >  }
> >  
> > +static vm_fault_t shmem_page_mkwrite(struct vm_fault *vmf)
> > +{
> > +	struct vm_area_struct *vma = vmf->vma;
> > +	struct inode *inode = file_inode(vma->vm_file);
> > +
> > +	file_update_time(vma->vm_file);
> > +	inode_inc_iversion(inode);
> > +	return 0;
> > +}
> > +
> >  unsigned long shmem_get_unmapped_area(struct file *file,
> >  				      unsigned long uaddr, unsigned long len,
> >  				      unsigned long pgoff, unsigned long flags)
> > @@ -4210,6 +4220,7 @@ static const struct super_operations shmem_ops = {
> >  
> >  static const struct vm_operations_struct shmem_vm_ops = {
> >  	.fault		= shmem_fault,
> > +	.page_mkwrite	= shmem_page_mkwrite,
> >  	.map_pages	= filemap_map_pages,
> >  #ifdef CONFIG_NUMA
> >  	.set_policy     = shmem_set_policy,
> > @@ -4219,6 +4230,7 @@ static const struct vm_operations_struct shmem_vm_ops = {
> >  
> >  static const struct vm_operations_struct shmem_anon_vm_ops = {
> >  	.fault		= shmem_fault,
> > +	.page_mkwrite	= shmem_page_mkwrite,
> >  	.map_pages	= filemap_map_pages,
> >  #ifdef CONFIG_NUMA
> >  	.set_policy     = shmem_set_policy,
> > 
> > -- 
> > 2.41.0

-- 
Jeff Layton <jlayton@...nel.org>

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