[Linux-cachefs] fscache.

[Gilliam, PaulX J]

Yudong,

There is a email list just for fscache, cachefiles and cachefs:
	linux-cachefs at redhat.com
It gets a lot less traffic than linux-nfs at vger.kernel.org and I don't know if one can find the same level of expertise monitoring it, I have seen David Howells there.  He is the author of fcache, cachefiles and cachefs.

-=# Paul Gilliam #=-


>-----Original Message-----
>From: linux-nfs-owner at vger.kernel.org [mailto:linux-nfs-
>owner at vger.kernel.org] On Behalf Of Yudong Gao
>Sent: Thursday, August 05, 2010 1:14 PM
>To: Trond Myklebust
>Cc: Andy Adamson; linux-nfs at vger.kernel.org
>Subject: Re: Write delegation
>
>Hi Trond,
>
>I just find the function nfs_fscache_set_inode_cookie() that checks
>the access flag and allows only read-only files to use the cache.
>
>Thanks!
>
>best,
>
>Yudong
>
>On Thu, Aug 5, 2010 at 11:10 AM, Yudong Gao <stgyd at umich.edu> wrote:
>> I see. I was kind of confused before. Sorry about that.
>>
>> I am trying to figure out how this read-only is supported in the
>> source code. When a page is read from the network through
>> nfs_readpage(), it will be cached to fscache, as implemented in
>> nfs_readpage_release(). The code in nfs_readpage_release() only checks
>> whether fscache is available, and if so, the page will be cached to
>> fscache.
>>
>> If a page is modified locally in memory (the page cache), then it
>> becomes dirty. But since the fscache is read-only, the copy of the
>> page in fscache becomes stale. When the file is close, the dirty page
>> will be written back to the server. Later when it is not used for a
>> while, it will be removed from the page cache. Here I suppose the copy
>> in fscache will not be deleted, or fscache becomes useless: it can
>> only mirror the pages in the page cache and does not provide extra
>> cache. And actually in the source code, I can not find the code to
>> uncache the page in fscache().
>>
>> So far so good. But if later this page is read again, the behavior
>> becomes strange. The nfs_readpage() checks first try to read the page
>> from fscache. In this case, it will read the stale page and oops!
>>
>> I think the problem here is that when a page become dirty in page
>> cache, it should be removed from fscache. So my question is where is
>> this implemented?
>>
>> Thanks a lot!
>>
>> best,
>>
>> Yudong
>>
>> On Wed, Aug 4, 2010 at 6:25 PM, Trond Myklebust
>> <trond.myklebust at fys.uio.no> wrote:
>>> On Wed, 2010-08-04 at 18:22 -0700, Yudong Gao wrote:
>>>
>>>> But for the integration with NFS, it is confusing. The
>>>> fscache_write_page() is called only in one place:
>>>> nfs_readpage_release(). So a NFS page is only written to fscache after
>>>> it is read from the server in nfs_readpage. So my question is, if a
>>>> page is locally modified, when its data is propagated to fscache? I
>>>> check the nfs_write_begin() and nfs_write_end() but cannot find any
>>>> relative implementation.
>>>
>>> See my previous answer. fscache only supports read-only files in NFS.
>>>
>>> Trond
>>>
>>>
>>
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