From: Lukas Czerner Subject: Re: [PATCH] ext4: speed up group trim with the right free block count. Date: Fri, 21 Jan 2011 11:49:21 +0100 (CET) Message-ID: References: <1295577131-3778-1-git-send-email-tm@tao.ma> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: linux-ext4@vger.kernel.org, "Theodore Ts'o" To: Tao Ma Return-path: Received: from mx1.redhat.com ([209.132.183.28]:19492 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753431Ab1AUKt2 (ORCPT ); Fri, 21 Jan 2011 05:49:28 -0500 In-Reply-To: <1295577131-3778-1-git-send-email-tm@tao.ma> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, 21 Jan 2011, Tao Ma wrote: > From: Tao Ma > > When we trim some free blocks in a group of ext4, we should > calculate the free blocks properly and check whether there are > enough freed blocks left for us to trim. Current solution will > only calculate free spaces if they are large for a trim which > isn't appropriate. > > Let us see a small example: > a group has 1.5M free which are 300k, 300k, 300k, 300k, 300k. > And minblocks is 1M. With current solution, we have to iterate > the whole group since these 300k will never be subtracted from > 1.5M. But actually we should exit after we find the first 2 > free spaces since the left 3 chunks only sum up to 900K if we > subtract the first 600K although they can't be trimed. > > Cc: "Theodore Ts'o" > Signed-off-by: Tao Ma > --- > fs/ext4/mballoc.c | 5 +++-- > 1 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 851f49b..970e471 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -4737,7 +4737,7 @@ ext4_grpblk_t ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b, > ext4_grpblk_t start, ext4_grpblk_t max, ext4_grpblk_t minblocks) > { > void *bitmap; > - ext4_grpblk_t next, count = 0; > + ext4_grpblk_t next, count = 0, free_count = 0; > ext4_group_t group; > int ret = 0; > > @@ -4762,6 +4762,7 @@ ext4_grpblk_t ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b, > break; > count += next - start; > } > + free_count += next - start; > start = next + 1; > > if (fatal_signal_pending(current)) { > @@ -4775,7 +4776,7 @@ ext4_grpblk_t ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b, > ext4_lock_group(sb, group); > } > > - if ((e4b->bd_info->bb_free - count) < minblocks) > + if ((e4b->bd_info->bb_free - free_count) < minblocks) > break; > } > ext4_unlock_group(sb, group); > Looks good, thanks. -Lukas