From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx141.postini.com [74.125.245.141]) by kanga.kvack.org (Postfix) with SMTP id 559C46B00EF for ; Sun, 25 Mar 2012 17:56:06 -0400 (EDT) Received: by pbcup15 with SMTP id up15so6346625pbc.14 for ; Sun, 25 Mar 2012 14:56:05 -0700 (PDT) Date: Sun, 25 Mar 2012 14:55:36 -0700 (PDT) From: Hugh Dickins Subject: Re: [PATCH] mm for fs: add truncate_pagecache_range In-Reply-To: <20120325135002.185b4caf.akpm@linux-foundation.org> Message-ID: References: <20120323140120.11f95cd5.akpm@linux-foundation.org> <20120323155950.f9bfb097.akpm@linux-foundation.org> <20120325135002.185b4caf.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Hugh Dickins , Christoph Hellwig , Theodore Ts'o , Al Viro , Alex Elder , Andreas Dilger , Ben Myers , Dave Chinner , Joel Becker , Mark Fasheh , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org On Sun, 25 Mar 2012, Andrew Morton wrote: > On Sun, 25 Mar 2012 13:26:10 -0700 (PDT) Hugh Dickins 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@kvack.org. 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: email@kvack.org