Re: [PATCH 35/45] xfs: introduce per-cpu CIL tracking sructure

Darrick J. Wong
2021-03-11T00:12:52Z

On Fri, Mar 05, 2021 at 04:11:33PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> The CIL push lock is highly contended on larger machines, becoming a
> hard bottleneck that about 700,000 transaction commits/s on >16p
> machines. To address this, start moving the CIL tracking
> infrastructure to utilise per-CPU structures.
>
> We need to track the space used, the amount of log reservation space
> reserved to write the CIL, the log items in the CIL and the busy
> extents that need to be completed by the CIL commit. This requires
> a couple of per-cpu counters, an unordered per-cpu list and a
> globally ordered per-cpu list.
>
> Create a per-cpu structure to hold these and all the management
> interfaces needed, as well as the hooks to handle hotplug CPUs.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_log_cil.c | 94 ++++++++++++++++++++++++++++++++++++++
> fs/xfs/xfs_log_priv.h | 15 ++++++
> include/linux/cpuhotplug.h | 1 +
> 3 files changed, 110 insertions(+)
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index f8fb2f59e24c..1bcf0d423d30 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -1365,6 +1365,93 @@ xfs_log_item_in_current_chkpt(
> return true;
> }
>
> +#ifdef CONFIG_HOTPLUG_CPU
> +static LIST_HEAD(xlog_cil_pcp_list);
> +static DEFINE_SPINLOCK(xlog_cil_pcp_lock);
> +static bool xlog_cil_pcp_init;
> +
> +static int
> +xlog_cil_pcp_dead(
> + unsigned int cpu)
> +{
> + struct xfs_cil *cil;
> +
> + spin_lock(&xlog_cil_pcp_lock);
> + list_for_each_entry(cil, &xlog_cil_pcp_list, xc_pcp_list) {

Weird indentation.

> + /* move stuff on dead CPU to context */

Should this have some actual code? I don't think any of the remaining
patches add anything here.

> + }
> + spin_unlock(&xlog_cil_pcp_lock);
> + return 0;
> +}
> +
> +static int
> +xlog_cil_pcp_hpadd(
> + struct xfs_cil *cil)
> +{
> + if (!xlog_cil_pcp_init) {
> + int ret;
> + ret = cpuhp_setup_state_nocalls(CPUHP_XFS_CIL_DEAD,
> + "xfs/cil_pcp:dead", NULL,
> + xlog_cil_pcp_dead);
> + if (ret < 0) {
> + xfs_warn(cil->xc_log->l_mp,
> + "Failed to initialise CIL hotplug, error %d. XFS is non-functional.",

How likely is to happen?

> + ret);
> + ASSERT(0);

I guess not that often?

> + return -ENOMEM;

Why not return ret here? I guess it's because ret could be any number
of (not centrally documented?) error codes, and we don't really care to
expose that to userspace?

--D

> + }
> + xlog_cil_pcp_init = true;
> + }
> +
> + INIT_LIST_HEAD(&cil->xc_pcp_list);
> + spin_lock(&xlog_cil_pcp_lock);
> + list_add(&cil->xc_pcp_list, &xlog_cil_pcp_list);
> + spin_unlock(&xlog_cil_pcp_lock);
> + return 0;
> +}
> +
> +static void
> +xlog_cil_pcp_hpremove(
> + struct xfs_cil *cil)
> +{
> + spin_lock(&xlog_cil_pcp_lock);
> + list_del(&cil->xc_pcp_list);
> + spin_unlock(&xlog_cil_pcp_lock);
> +}
> +
> +#else /* !CONFIG_HOTPLUG_CPU */
> +static inline void xlog_cil_pcp_hpadd(struct xfs_cil *cil) {}
> +static inline void xlog_cil_pcp_hpremove(struct xfs_cil *cil) {}
> +#endif
> +
> +static void __percpu *
> +xlog_cil_pcp_alloc(
> + struct xfs_cil *cil)
> +{
> + struct xlog_cil_pcp *cilpcp;
> +
> + cilpcp = alloc_percpu(struct xlog_cil_pcp);
> + if (!cilpcp)
> + return NULL;
> +
> + if (xlog_cil_pcp_hpadd(cil) < 0) {
> + free_percpu(cilpcp);
> + return NULL;
> + }
> + return cilpcp;
> +}
> +
> +static void
> +xlog_cil_pcp_free(
> + struct xfs_cil *cil,
> + struct xlog_cil_pcp *cilpcp)
> +{
> + if (!cilpcp)
> + return;
> + xlog_cil_pcp_hpremove(cil);
> + free_percpu(cilpcp);
> +}
> +
> /*
> * Perform initial CIL structure initialisation.
> */
> @@ -1379,6 +1466,12 @@ xlog_cil_init(
> if (!cil)
> return -ENOMEM;
>
> + cil->xc_pcp = xlog_cil_pcp_alloc(cil);
> + if (!cil->xc_pcp) {
> + kmem_free(cil);
> + return -ENOMEM;
> + }
> +
> INIT_LIST_HEAD(&cil->xc_cil);
> INIT_LIST_HEAD(&cil->xc_committing);
> spin_lock_init(&cil->xc_cil_lock);
> @@ -1409,6 +1502,7 @@ xlog_cil_destroy(
>
> ASSERT(list_empty(&cil->xc_cil));
> ASSERT(test_bit(XLOG_CIL_EMPTY, &cil->xc_flags));
> + xlog_cil_pcp_free(cil, cil->xc_pcp);
> kmem_free(cil);
> }
>
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index e72d14c76e03..2562f29c8986 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -231,6 +231,16 @@ struct xfs_cil_ctx {
> struct work_struct push_work;
> };
>
> +/*
> + * Per-cpu CIL tracking items
> + */
> +struct xlog_cil_pcp {
> + uint32_t space_used;
> + uint32_t curr_res;
> + struct list_head busy_extents;
> + struct list_head log_items;
> +};
> +
> /*
> * Committed Item List structure
> *
> @@ -264,6 +274,11 @@ struct xfs_cil {
> wait_queue_head_t xc_commit_wait;
> xfs_csn_t xc_current_sequence;
> wait_queue_head_t xc_push_wait; /* background push throttle */
> +
> + struct xlog_cil_pcp __percpu *xc_pcp;
> +#ifdef CONFIG_HOTPLUG_CPU
> + struct list_head xc_pcp_list;
> +#endif
> } ____cacheline_aligned_in_smp;
>
> /* xc_flags bit values */
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index f14adb882338..b13b21d825b3 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -52,6 +52,7 @@ enum cpuhp_state {
> CPUHP_FS_BUFF_DEAD,
> CPUHP_PRINTK_DEAD,
> CPUHP_MM_MEMCQ_DEAD,
> + CPUHP_XFS_CIL_DEAD,
> CPUHP_PERCPU_CNT_DEAD,
> CPUHP_RADIX_DEAD,
> CPUHP_PAGE_ALLOC_DEAD,
> --
> 2.28.0
>