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@xxxxxxxxx> 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@xxxxxxxxxx> 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 >> >> > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
