Re: [PATCH] ceph: Update the pages in fscache in writepages() path

[Milosz Tanski]

Li,

First, sorry for the late reply on this.

Currently fscache is only supported for files that are open in read
only mode. I originally was going to let fscache cache in the write
path as well as long as the file was open in with O_LAZY. I abandoned
that idea. When a user opens the file in O_LAZY we can cache things
locally with the assumption that the user will care of the
synchronization in some other manner. There is no way of invalidating
a subset of the pages in object cached by fscache, there is no way we
can make O_LAZY work well.

The ceph_readpage_to_fscache() in writepage has no effect and it
should be removed. ceph_readpage_to_fscache() calls cache_valid() to
see if it should perform the page save, and since the file can't have
a CACHE cap at the point in time it doesn't do it.

Thanks,
- Milosz

On Thu, Oct 31, 2013 at 11:56 PM, Li Wang <liwang@xxxxxxxxxxxxxxx> wrote:
> Currently, the pages in fscache only are updated in writepage() path,
> add the process in writepages().
>
> Signed-off-by: Min Chen <minchen@xxxxxxxxxxxxxxx>
> Signed-off-by: Li Wang <liwang@xxxxxxxxxxxxxxx>
> Signed-off-by: Yunchuan Wen <yunchuanwen@xxxxxxxxxxxxxxx>
> ---
>  fs/ceph/addr.c |    8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index 6df8bd4..cc57911 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -746,7 +746,7 @@ retry:
>
>         while (!done && index <= end) {
>                 int num_ops = do_sync ? 2 : 1;
> -               unsigned i;
> +               unsigned i, j;
>                 int first;
>                 pgoff_t next;
>                 int pvec_pages, locked_pages;
> @@ -894,7 +894,6 @@ get_more_pages:
>                 if (!locked_pages)
>                         goto release_pvec_pages;
>                 if (i) {
> -                       int j;
>                         BUG_ON(!locked_pages || first < 0);
>
>                         if (pvec_pages && i == pvec_pages &&
> @@ -924,7 +923,10 @@ get_more_pages:
>
>                 osd_req_op_extent_osd_data_pages(req, 0, pages, len, 0,
>                                                         !!pool, false);
> -
> +               for(j = 0; j < locked_pages; j++) {
> +                       struct page *page = pages[j];
> +                       ceph_readpage_to_fscache(inode, page);
> +               }
>                 pages = NULL;   /* request message now owns the pages array */
>                 pool = NULL;
>
> --
> 1.7.9.5
>
> --
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-- 
Milosz Tanski
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