Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752217AbdLYDpG (ORCPT ); Sun, 24 Dec 2017 22:45:06 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:2782 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751039AbdLYDpC (ORCPT ); Sun, 24 Dec 2017 22:45:02 -0500 Subject: Re: [PATCH] f2fs: avoid f2fs_gc dead loop To: Yunlong Song , , , CC: , , , , , References: <1514034550-149813-1-git-send-email-yunlong.song@huawei.com> From: Chao Yu Message-ID: <4202ea25-f40a-a4da-787b-86f5aa9b0311@huawei.com> Date: Mon, 25 Dec 2017 11:44:36 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <1514034550-149813-1-git-send-email-yunlong.song@huawei.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4185 Lines: 129 On 2017/12/23 21:09, Yunlong Song wrote: > For some corner case, f2fs_gc selects one target victim but cannot free > that victim segment due to some reason (e.g. the segment has some blocks > of atomic file which is not commited yet), in this case, the victim File should not be atomic opened for long time since normally sqlite transaction will finish quickly, so we can expect that gc loop could be ended up soon, right? Thanks, > segment may probably be selected over and over, and then f2fs_gc will > go to dead loop. This patch identifies the dead-loop segment, and skips > it in __get_victim next time. > > Signed-off-by: Yunlong Song > --- > fs/f2fs/f2fs.h | 8 ++++++++ > fs/f2fs/gc.c | 34 ++++++++++++++++++++++++++++++++++ > fs/f2fs/super.c | 3 +++ > 3 files changed, 45 insertions(+) > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h > index ca6b0c9..b75851b 100644 > --- a/fs/f2fs/f2fs.h > +++ b/fs/f2fs/f2fs.h > @@ -115,6 +115,13 @@ struct f2fs_mount_info { > unsigned int opt; > }; > > +struct gc_loop_info { > + int count; > + unsigned int segno; > + unsigned long *segmap; > +}; > +#define GC_LOOP_MAX 10 > + > #define F2FS_FEATURE_ENCRYPT 0x0001 > #define F2FS_FEATURE_BLKZONED 0x0002 > #define F2FS_FEATURE_ATOMIC_WRITE 0x0004 > @@ -1125,6 +1132,7 @@ struct f2fs_sb_info { > > /* threshold for converting bg victims for fg */ > u64 fggc_threshold; > + struct gc_loop_info gc_loop; > > /* maximum # of trials to find a victim segment for SSR and GC */ > unsigned int max_victim_search; > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c > index 5d5bba4..4ee9e1b 100644 > --- a/fs/f2fs/gc.c > +++ b/fs/f2fs/gc.c > @@ -229,6 +229,10 @@ static unsigned int check_bg_victims(struct f2fs_sb_info *sbi) > if (no_fggc_candidate(sbi, secno)) > continue; > > + if (sbi->gc_loop.segmap && > + test_bit(GET_SEG_FROM_SEC(sbi, secno), sbi->gc_loop.segmap)) > + continue; > + > clear_bit(secno, dirty_i->victim_secmap); > return GET_SEG_FROM_SEC(sbi, secno); > } > @@ -371,6 +375,9 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi, > if (gc_type == FG_GC && p.alloc_mode == LFS && > no_fggc_candidate(sbi, secno)) > goto next; > + if (gc_type == FG_GC && p.alloc_mode == LFS && > + sbi->gc_loop.segmap && test_bit(segno, sbi->gc_loop.segmap)) > + goto next; > > cost = get_gc_cost(sbi, segno, &p); > > @@ -1042,6 +1049,27 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, > seg_freed = do_garbage_collect(sbi, segno, &gc_list, gc_type); > if (gc_type == FG_GC && seg_freed == sbi->segs_per_sec) > sec_freed++; > + else if (gc_type == FG_GC && seg_freed == 0) { > + if (!sbi->gc_loop.segmap) { > + sbi->gc_loop.segmap = > + kvzalloc(f2fs_bitmap_size(MAIN_SEGS(sbi)), GFP_KERNEL); > + sbi->gc_loop.count = 0; > + sbi->gc_loop.segno = NULL_SEGNO; > + } > + if (segno == sbi->gc_loop.segno) { > + if (sbi->gc_loop.count > GC_LOOP_MAX) { > + f2fs_bug_on(sbi, 1); > + set_bit(segno, sbi->gc_loop.segmap); > + sbi->gc_loop.count = 0; > + sbi->gc_loop.segno = NULL_SEGNO; > + } > + else > + sbi->gc_loop.count++; > + } else { > + sbi->gc_loop.segno = segno; > + sbi->gc_loop.count = 0; > + } > + } > total_freed += seg_freed; > > if (gc_type == FG_GC) > @@ -1075,6 +1103,12 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, > > if (sync) > ret = sec_freed ? 0 : -EAGAIN; > + if (sbi->gc_loop.segmap) { > + kvfree(sbi->gc_loop.segmap); > + sbi->gc_loop.segmap = NULL; > + sbi->gc_loop.count = 0; > + sbi->gc_loop.segno = NULL_SEGNO; > + } > return ret; > } > > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c > index 031cb26..76f0b72 100644 > --- a/fs/f2fs/super.c > +++ b/fs/f2fs/super.c > @@ -2562,6 +2562,9 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent) > sbi->last_valid_block_count = sbi->total_valid_block_count; > sbi->reserved_blocks = 0; > sbi->current_reserved_blocks = 0; > + sbi->gc_loop.segmap = NULL; > + sbi->gc_loop.count = 0; > + sbi->gc_loop.segno = NULL_SEGNO; > > for (i = 0; i < NR_INODE_TYPE; i++) { > INIT_LIST_HEAD(&sbi->inode_list[i]); >