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Date:   Tue, 25 Jul 2023 18:39:25 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Jeff Layton <jlayton@kernel.org>
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Subject: Re: [PATCH v6 3/7] tmpfs: bump the mtime/ctime/iversion when page
 becomes writeable
In-Reply-To: <20230725-mgctime-v6-3-a794c2b7abca@kernel.org>
Message-ID: <42c5bbe-a7a4-3546-e898-3f33bd71b062@google.com>
References: <20230725-mgctime-v6-0-a794c2b7abca@kernel.org> <20230725-mgctime-v6-3-a794c2b7abca@kernel.org>
MIME-Version: 1.0
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Precedence: bulk

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

> 
> Signed-off-by: Jeff Layton <jlayton@kernel.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