From: Namjae Jeon Subject: Re: [PATCH RESEND 0/10] fs: Introduce new flag(FALLOC_FL_COLLAPSE_RANGE) for fallocate Date: Wed, 19 Feb 2014 09:46:04 +0900 Message-ID: References: <1391319694-3089-1-git-send-email-linkinjeon@gmail.com> <20140202151624.GK20939@parisc-linux.org> <20140202152106.GL20939@parisc-linux.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: tytso@mit.edu, Namjae Jeon , linux-kernel@vger.kernel.org, xfs@oss.sgi.com, bpm@sgi.com, adilger.kernel@dilger.ca, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, jack@suse.cz, linux-ext4@vger.kernel.org, mtk.manpages@gmail.com To: Matthew Wilcox Return-path: In-Reply-To: <20140202152106.GL20939@parisc-linux.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com List-Id: linux-ext4.vger.kernel.org 2014-02-03 0:21 GMT+09:00, Matthew Wilcox : > On Sun, Feb 02, 2014 at 08:16:24AM -0700, Matthew Wilcox wrote: >> On Sun, Feb 02, 2014 at 02:41:34PM +0900, Namjae Jeon wrote: >> > The semantics of this flag are following: >> > 1) It collapses the range lying between offset and length by removing >> > any data >> > blocks which are present in this range and than updates all the >> > logical >> > offsets of extents beyond "offset + len" to nullify the hole created >> > by >> > removing blocks. In short, it does not leave a hole. >> > 2) It should be used exclusively. No other fallocate flag in >> > combination. >> > 3) Offset and length supplied to fallocate should be fs block size >> > aligned >> > in case of xfs and ext4. >> > 4) Collaspe range does not work beyond i_size. >> >> What if the file is mmaped at the time somebody issues this command? >> Seems to me we should drop pagecache pages that overlap with the >> removed blocks. If the removed range is not a multiple of PAGE_SIZE, >> then we should also drop any pagecache pages after the removed range. Hi Matthew. Yes, right. So both xfs and ext4 call truncate_pagecache_range to drop page caches before removing blocks. truncate_pagecache_range(inode, offset, -1); and end offset is -1, which mean all page cache will be dropped from start offset to the end of file. > > Oops, forgot to add "and if it is a multiple of page size, then we need > to update the offsets of any pages after the removed page". We should > probably start easy though; just drop all pages that overlap the beginning > of the affected range to the end of the file. Yes, right. current implementation does exactly as you pointed > At some later point, > if there's demand, we can add the optimisation to adjust the offsets of > pages still in the cache. -> Yes, Right. But if we consider that fs block size can be less than page cache size,(512B, 1K, 2K) I thought that it is proper to drop all pages from the start offset to the end of the file. Thanks for your reply. > > -- > Matthew Wilcox Intel Open Source Technology Centre > "Bill, look, we understand that you're interested in selling us this > operating system, but compare it to ours. We can't possibly take such > a retrograde step." > _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs