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
