On 05/03/2012 05:43 PM, Myklebust, Trond wrote: > On Thu, 2012-05-03 at 17:34 +0200, Niels de Vos wrote: >> When an application on an NFS-client (tested with NFSv3) executes the >> following steps, data written after the close() is never flushed to the >> server: >> >> 1. open() >> 2. mmap() >> 3. close() >> 4.<modify data in the mmap'ed area> >> 5. munmap() >> >> Dropping the caches (via /proc/sys/vm/drop_caches) or unmounting does not >> result in the data being sent to the server. >> >> The man-page for mmap (man 2 mmap) does mention that closing the file- >> descriptor does not munmap() the area. Using the mmap'ed area after a >> close() sound valid to me (even if it may be bad practice). >> >> Investigation and checking showed that the NFS-client does not handle >> munmap(), and only flushes on close(). To solve this problem, least two >> solutions can be proposed: >> >> a. f_ops->release() is called on munmap() as well as on close(), >> therefore release() can be used to flush data as well. >> b. In the 'struct vm_operations_struct' add a .close to the >> 'struct vm_area_struct' on calling mmap()/nfs_file_mmap() and flush >> the data in the new close() function. >> >> Solution a. contains currently very few code changes: >> >> --- a/fs/nfs/inode.c >> +++ b/fs/nfs/inode.c >> @@ -713,6 +713,8 @@ int nfs_open(struct inode *inode, struct file *filp) >> >> int nfs_release(struct inode *inode, struct file *filp) >> { >> + if (S_ISREG(inode->i_mode)&& inode->i_mapping->nrpages != 0) { >> + nfs_sync_mapping(inode->i_mapping); >> nfs_file_clear_open_context(filp); >> return 0; >> } >> >> The disadvantage is, that nfs_release() is called on close() too. That >> means this causes a flushing of dirty pages, and just after that the >> nfs_file_clear_open_context() might flush again. The advantage is that >> it is possible (though not done at the moment) to return an error in >> case flushing failed. >> >> Solution b. does not provide an option to return an error, but does not >> get called on each close(): >> >> --- a/fs/nfs/file.c >> +++ b/fs/nfs/file.c >> @@ -547,9 +547,17 @@ out: >> return ret; >> } >> >> +static void nfs_vm_close(struct vm_area_struct * vma) >> +{ >> + struct file *filp = vma->vm_file; >> + >> + nfs_file_flush(filp, (fl_owner_t)filp); >> +} >> + >> static const struct vm_operations_struct nfs_file_vm_ops = { >> .fault = filemap_fault, >> .page_mkwrite = nfs_vm_page_mkwrite, >> + .close = nfs_vm_close, >> }; >> >> static int nfs_need_sync_write(struct file *filp, struct inode *inode) >> >> I would like some feedback on what solution is most acceptable, or any >> other suggestions. > > Neither solution is acceptable. This isn't a close-to-open cache > consistency issue. > > The syntax of mmap() for both block and NFS mounts is the same: writes > are not guaranteed to hit the disk until your application explicitly > calls msync(). > Okay, that makes sense. But if the application never calls msync(), and just munmap()'s the area, when should the changes be written? I did not expect that unmounting just disregards the data. Any suggestions on correcting this (if it should be corrected) are welcome. Thanks again, Niels -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html