From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] ext4: Remove extent tree purging from ext4_da_page_release_reservation() Date: Wed, 24 Jul 2013 22:05:36 +0200 Message-ID: <20130724200536.GC27307@quack.suse.cz> References: <1374099015-6829-1-git-send-email-jack@suse.cz> <20130719004439.GA21615@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Ted Tso , linux-ext4@vger.kernel.org, Zheng Liu To: Zheng Liu Return-path: Received: from cantor2.suse.de ([195.135.220.15]:44549 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752155Ab3GXUF7 (ORCPT ); Wed, 24 Jul 2013 16:05:59 -0400 Content-Disposition: inline In-Reply-To: <20130719004439.GA21615@gmail.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Hi Zheng, On Fri 19-07-13 08:44:39, Zheng Liu wrote: > On Thu, Jul 18, 2013 at 12:10:15AM +0200, Jan Kara wrote: > > ext4_da_page_release_reservation() gets called from > > ext4_da_invalidatepage(). This function is used when we are truncating > > page cache for punch hole or truncate operations. In either case these > > operations take care of removing extents from the extent tree. This is > > more efficient and the code in ext4_da_page_release_reservation() is > > actually buggy anyway. So just remove it. > > I remember that I try to remove the entry from extent status tree here > because at the end of this function it tries to relase the reserved > space for delalloc. For 4k block we can simply release it because > ->s_cluster_ratio == 1. But when bigalloc is enabled, we need to > determine whether we can release the reserved space according to the > result of ext4_find_delalloc_cluster() as the comment described. If we > don't remove the entry from extent status tree here, we could lost some > spaces that could be reused by other files. If I remember correctly, I > have hitted a warning message when I run xfstests to test it. These > days I try to trigger it using xfstests but I failed. Have you seen a > prblem that is caused by this code? Maybe we need to refactor out the > code and release the reserved space outside this function. Ah, I see. No, I didn't observe any problem due to this code, I just didn't understand why is it there. Also when blocksize < pagesize, the code is wrong because delayed buffers to release need not be contiguous so ext4_es_remove_extent(inode, lblk, to_release) may not free all the buffers we want. But subsequent extent tree truncation in ext4_ext_truncate() hides this problem. So I think we might just change the condition: if (to_release) { to if (to_release && sbi->s_cluster_ratio > 1) { and add explanatory comment why cluster_ratio > 1 needs the truncation and other cases don't. It will also save some needlessly burned CPU cycles spent when manipulating extent tree. Honza -- Jan Kara SUSE Labs, CR