From: Dmitry Monakhov Subject: [PATCH] ext4: improve ext4lazyinit scalability Date: Tue, 19 Jul 2016 16:30:32 +0400 Message-ID: <1468931432-1568-1-git-send-email-dmonakhov@openvz.org> Cc: tytso@mit.edu, Dmitry Monakhov To: linux-ext4@vger.kernel.org Return-path: Received: from mailhub.sw.ru ([195.214.232.25]:5635 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753047AbcGSNKS (ORCPT ); Tue, 19 Jul 2016 09:10:18 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: ext4lazyinit is global thread. This thread performs itable initalization under It basically does followes: ext4_lazyinit_thread ->mutex_lock(&eli->li_list_mtx); ->ext4_run_li_request(elr) ->ext4_init_inode_table-> Do a lot of IO if list is large And when new mounts/umount arrives they have to block on ->li_list_mtx because lazy_thread holds it during full walk procedure. ext4_fill_super ->ext4_register_li_request ->mutex_lock(&ext4_li_info->li_list_mtx); ->list_add(&elr->lr_request, &ext4_li_info >li_request_list); In my case mount takes 40minutes on server with 36 * 4Tb HDD. Convenient user may face this in case of very slow dev ( /dev/mmcblkXXX) Even more. I one of filesystem was frozen lazyinit_thread will simply blocks on sb_start_write() so other mount/umounts will suck forever. This patch changes logic like follows: - grap ->s_umount read sem before process new li_request after that it is safe to drop list_mtx because all callers of li_remove_requers are holds ->s_umount for write. - li_thread skip frozen SB's Locking: Locking order is asserted by umout path like follows: s_umount ->li_list_mtx so the only way to to grab ->s_mount inside li_thread is via down_read_trylock xfstests:ext4/022 message-id:1468931005-774-1-git-send-email-dmonakhov@openvz.org #PSBM-49658 Signed-off-by: Dmitry Monakhov --- fs/ext4/super.c | 53 ++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 36 insertions(+), 17 deletions(-) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 3822a5a..0ee193f 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -2635,7 +2635,6 @@ static int ext4_run_li_request(struct ext4_li_request *elr) sb = elr->lr_super; ngroups = EXT4_SB(sb)->s_groups_count; - sb_start_write(sb); for (group = elr->lr_next_group; group < ngroups; group++) { gdp = ext4_get_group_desc(sb, group, NULL); if (!gdp) { @@ -2662,8 +2661,6 @@ static int ext4_run_li_request(struct ext4_li_request *elr) elr->lr_next_sched = jiffies + elr->lr_timeout; elr->lr_next_group = group + 1; } - sb_end_write(sb); - return ret; } @@ -2713,9 +2710,9 @@ static struct task_struct *ext4_lazyinit_task; static int ext4_lazyinit_thread(void *arg) { struct ext4_lazy_init *eli = (struct ext4_lazy_init *)arg; - struct list_head *pos, *n; struct ext4_li_request *elr; unsigned long next_wakeup, cur; + LIST_HEAD(request_list); BUG_ON(NULL == eli); @@ -2728,21 +2725,43 @@ cont_thread: mutex_unlock(&eli->li_list_mtx); goto exit_thread; } - - list_for_each_safe(pos, n, &eli->li_request_list) { - elr = list_entry(pos, struct ext4_li_request, - lr_request); - - if (time_after_eq(jiffies, elr->lr_next_sched)) { - if (ext4_run_li_request(elr) != 0) { - /* error, remove the lazy_init job */ - ext4_remove_li_request(elr); - continue; + list_splice_init(&eli->li_request_list, &request_list); + while (!list_empty(&request_list)) { + int err = 0; + int progress = 0; + + elr = list_entry(request_list.next, + struct ext4_li_request, lr_request); + list_move(request_list.next, &eli->li_request_list); + if (time_before(jiffies, elr->lr_next_sched)) { + if (time_before(elr->lr_next_sched, next_wakeup)) + next_wakeup = elr->lr_next_sched; + continue; + } + if (down_read_trylock(&elr->lr_super->s_umount)) { + if (sb_start_write_trylock(elr->lr_super)) { + progress = 1; + /* We holds sb->s_umount, sb can not + * be removed from the list, it is + * now safe to drop li_list_mtx + */ + mutex_unlock(&eli->li_list_mtx); + err = ext4_run_li_request(elr); + sb_end_write(elr->lr_super); + mutex_lock(&eli->li_list_mtx); } + up_read((&elr->lr_super->s_umount)); + } + /* error, remove the lazy_init job */ + if (err) { + ext4_remove_li_request(elr); + continue; + } + if (!progress) { + elr->lr_next_sched = jiffies + + (prandom_u32() + % (EXT4_DEF_LI_MAX_START_DELAY * HZ)); }