On Sun, 25 Mar 2012, Andrew Morton wrote: > On Sun, 25 Mar 2012 13:26:10 -0700 (PDT) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > truncate_pagecache_range() is just a drop-in replacement for > > truncate_inode_pages_range(), and has no different locking needs. > > Does anything prevent new pages from getting added to pagecache and > perhaps faulted into VMAs after or during the execution of these > functions? If a page is faulted into a vma after the unmap_mapping_range() but before truncate_inode_pages_range() reaches it, then it gets unmapped by the fallback unmap_mapping_range(), called from truncate_inode_page() while holding page lock. A new page could be faulted in a moment after; but last year I did change truncate_inode_pages_range() slightly, pinching down on the range instead of just the ascending linear scan, so it doesn't return until the range is empty of pages (excepting rcu races, which I think mean there's no exact instant of return which all cpus would agree upon). A new page could be faulted in a moment after that, and then it survives: unlike in the truncation case, there's no equivalent of i_size to determine whether to SIGBUS. (But even in the truncation case, a truncate or write to increase i_size may follow an instant later.) Individual filesystems may impose additional constraints to guarantee their own internal consistency; and tmpfs certainly finds inode->i_mutex useful for that, to serialize between holepunch and truncate and write. I wouldn't be surprised if other filesystems found it useful too, but that's up to them - truncate_pagecache_range() doesn't need it. > > Also, I wonder what prevents pages in the range from being dirtied > between ext4_ext_punch_hole()'s filemap_write_and_wait_range() and > truncate_inode_pages_range(). I'm not going to guess on that, or whether it matters: Ted? Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>