On Aug 16, 2017, at 9:41 AM, Jan Kara <jack@xxxxxxx> wrote:
>
> dq_data_lock is currently used to protect all modifications of quota
> accounting information, consistency of quota accounting on the inode,
> and dquot pointers from inode. As a result contention on the lock can be
> pretty heavy.
>
> Reduce the contention on the lock by protecting quota accounting
> information by a new dquot->dq_dqb_lock and consistency of quota
> accounting with inode usage by inode->i_lock.
>
> This change reduces time to create 500000 files on ext4 on ramdisk by 50
> different processes in separate directories by 6% when user quota is
> turned on. When those 50 processes belong to 50 different users, the
> improvement is about 9%.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
>
> @@ -1604,33 +1628,41 @@ int __dquot_alloc_space(struct inode *inode, qsize_t number, int flags)
>
> dquots = i_dquot(inode);
> index = srcu_read_lock(&dquot_srcu);
> - spin_lock(&dq_data_lock);
> + spin_lock(&inode->i_lock);
> for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
> if (!dquots[cnt])
> continue;
> - ret = check_bdq(dquots[cnt], number,
> - !(flags & DQUOT_SPACE_WARN), &warn[cnt]);
> - if (ret && !(flags & DQUOT_SPACE_NOFAIL)) {
> - spin_unlock(&dq_data_lock);
> + if (flags & DQUOT_SPACE_RESERVE) {
> + ret = dquot_add_space(dquots[cnt], 0, number, flags,
> + &warn[cnt]);
> + } else {
> + ret = dquot_add_space(dquots[cnt], number, 0, flags,
> + &warn[cnt]);
> + }
Minor nit - no need for braces around these single-line functions.
> diff --git a/include/linux/quota.h b/include/linux/quota.h
> index eccc1cb6274e..4b5180efff21 100644
> --- a/include/linux/quota.h
> +++ b/include/linux/quota.h
> @@ -298,6 +298,7 @@ struct dquot {
> struct list_head dq_free; /* Free list element */
> struct list_head dq_dirty; /* List of dirty dquots */
> struct mutex dq_lock; /* dquot IO lock */
> + spinlock_t dq_dqb_lock; /* Lock protecting dq_dqb changes */
Might be good to have a comment at mem_dqblk that dq_lock is used for locking?
Cheers, Andreas
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