åå: Re: [RFC PATCH 0/8] dax: Add a dax-rmap tree to support reflink

[Ruan, Shiyang]

å 2020/4/27 20:28:36, "Matthew Wilcox" <willy@xxxxxxxxxxxxx> åé:

>On Mon, Apr 27, 2020 at 04:47:42PM +0800, Shiyang Ruan wrote:
>>  This patchset is a try to resolve the shared 'page cache' problem for
>>  fsdax.
>>
>>  In order to track multiple mappings and indexes on one page, I
>>  introduced a dax-rmap rb-tree to manage the relationship.  A dax entry
>>  will be associated more than once if is shared.  At the second time we
>>  associate this entry, we create this rb-tree and store its root in
>>  page->private(not used in fsdax).  Insert (->mapping, ->index) when
>>  dax_associate_entry() and delete it when dax_disassociate_entry().
>
>Do we really want to track all of this on a per-page basis?  I would
>have thought a per-extent basis was more useful.  Essentially, create
>a new address_space for each shared extent.  Per page just seems like
>a huge overhead.
>
Per-extent tracking is a nice idea for me.  I haven't thought of it 
yet...

But the extent info is maintained by filesystem.  I think we need a way 
to obtain this info from FS when associating a page.  May be a bit 
complicated.  Let me think about it...


--
Thanks,
Ruan Shiyang.