ext4: improve ext4lazyinit scalability (e22834f0) · Commits · 戴 / test

ext4lazyinit is a global thread. This thread performs itable initalization under li_list_mtx mutex. It basically does the following: ext4_lazyinit_thread ->mutex_lock(&eli->li_list_mtx); ->ext4_run_li_request(elr) ->ext4_init_inode_table-> Do a lot of IO if the list is large And when new mount/umount arrive 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. Common user may face this in case of very slow dev ( /dev/mmcblkXXX) Even more. If one of filesystems was frozen lazyinit_thread will simply block on sb_start_write() so other mount/umount will be stuck forever. This patch changes logic like follows: - grab ->s_umount read sem before processing new li_request. After that it is safe to drop li_list_mtx because all callers of li_remove_request are holding ->s_umount for write. - li_thread skips frozen SB's Locking order: Mh KOrder is asserted by umount 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:ext4/023 #PSBM-49658 Signed-off-by:

Dmitry Monakhov <dmonakhov@openvz.org> Signed-off-by:

Theodore Ts'o <tytso@mit.edu>

fs/ext4/super.c

+31 −10

Original line number	Diff line number	Diff line
		@@ -2749,7 +2749,6 @@ 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) {
		@@ -2776,8 +2775,6 @@ 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;
		}

		@@ -2842,19 +2839,43 @@ cont_thread:
		mutex_unlock(&eli->li_list_mtx);
		goto exit_thread;
		}

		list_for_each_safe(pos, n, &eli->li_request_list) {
		int err = 0;
		int progress = 0;
		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) {
		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 hold 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);
		n = pos->next;
		}
		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));
		}

		if (time_before(elr->lr_next_sched, next_wakeup))
		next_wakeup = elr->lr_next_sched;
		}

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