Re: [GIT PULL] Backing device changes for 3.20

From: Linus Torvalds
Date: Thu Feb 12 2015 - 17:05:09 EST


On Thu, Feb 12, 2015 at 12:38 PM, Jens Axboe <axboe@xxxxxx> wrote:
>
> This pull request contains a cleanup of how the backing device is
> handled, in preparation for a rework of the life time rules. In this
> part, the most important change is to split the unrelated nommu mmap
> flags from it, but also removing a backing_dev_info pointer from the
> address_space (and inode), and a cleanup of other various minor bits.

Ugh, so this has a semantic conflict with the NFS client, that has
this particular code:

if (!cinfo->dreq) {
inc_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
- inc_bdi_stat(page_file_mapping(req->wb_page)->backing_dev_info,
+
inc_bdi_stat(inode_to_bdi(page_file_mapping(req->wb_page)->host),
BDI_RECLAIMABLE);
__mark_inode_dirty(req->wb_context->dentry->d_inode,
I_DIRTY_DATASYNC);
}

duplicated several times, and now one more time in the new
fs/nfs/flexfilelayout/flexfilelayout.c file.

I fixed it the same way it was fixed everywhere else, but while fixing
and looking at the cases, I *really* feel like the nfs code needs some
cleaning up.

That insane complicated and unexplained code exists three times: in
filelayout/filelayout.c, flexfilelayout/flexfilelayout.c and in
write.c.

The "reverse" case (which does the decrements, and doesn't mark the
inode dirty) exists a few more times.

Could we make that a helper function, with a few comments. For
example, looking at it, I wonder if

- page_file_mapping(req->wb_page)->host
- req->wb_context->dentry->d_inode

are the same inode?

Hmm?

Linus
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