Re: [RFC PATCH 0/8] fsdax: introduce FS query interface to support reflink

From: Ruan Shiyang
Date: Mon Aug 10 2020 - 04:16:09 EST

On 2020/8/7 下午9:38, Matthew Wilcox wrote:
On Fri, Aug 07, 2020 at 09:13:28PM +0800, Shiyang Ruan wrote:
This patchset is a try to resolve the problem of tracking shared page
for fsdax.

Instead of per-page tracking method, this patchset introduces a query
interface: get_shared_files(), which is implemented by each FS, to
obtain the owners of a shared page. It returns an owner list of this
shared page. Then, the memory-failure() iterates the list to be able
to notify each process using files that sharing this page.

The design of the tracking method is as follow:
1. dax_assocaite_entry() associates the owner's info to this page

I think that's the first problem with this design. dax_associate_entry is
a horrendous idea which needs to be ripped out, not made more important.
It's all part of the general problem of trying to do something on a
per-page basis instead of per-extent basis.

The memory-failure needs to track owners info from a dax page, so I should associate the owner with this page. In this version, I associate the block device to the dax page, so that the memory-failure is able to iterate the owners by the query interface provided by filesystem.

Ruan Shiyang.