[PATCH 1/3] staging: lustre: osc: add and fixup comments for LRU handling

From: James Simmons
Date: Thu Dec 01 2016 - 17:38:09 EST


From: Jinshan Xiong <jinshan.xiong@xxxxxxxxx>

Add new information about the fields in struct client_obd.

Signed-off-by: Jinshan Xiong <jinshan.xiong@xxxxxxxxx>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5108
Reviewed-on: http://review.whamcloud.com/10458
Reviewed-by: Bobi Jam <bobijam@xxxxxxxxxxx>
Reviewed-by: Fan Yong <fan.yong@xxxxxxxxx>
Reviewed-by: Oleg Drokin <oleg.drokin@xxxxxxxxx>
Signed-off-by: James Simmons <jsimmons@xxxxxxxxxxxxx>
---
drivers/staging/lustre/lustre/include/obd.h | 27 ++++++++++++++++++++++---
drivers/staging/lustre/lustre/osc/osc_page.c | 17 +++++++++++----
2 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/lustre/lustre/include/obd.h b/drivers/staging/lustre/lustre/include/obd.h
index d4d2ffa..6d6e479 100644
--- a/drivers/staging/lustre/lustre/include/obd.h
+++ b/drivers/staging/lustre/lustre/include/obd.h
@@ -247,15 +247,34 @@ struct client_obd {
struct obd_histogram cl_read_offset_hist;
struct obd_histogram cl_write_offset_hist;

- /* lru for osc caching pages */
+ /* LRU for osc caching pages */
struct cl_client_cache *cl_cache;
- struct list_head cl_lru_osc; /* member of cl_cache->ccc_lru */
+ /** member of cl_cache->ccc_lru */
+ struct list_head cl_lru_osc;
+ /** # of available LRU slots left in the per-OSC cache.
+ * Available LRU slots are shared by all OSCs of the same file system,
+ * therefore this is a pointer to cl_client_cache::ccc_lru_left.
+ */
atomic_long_t *cl_lru_left;
+ /** # of busy LRU pages. A page is considered busy if it's in writeback
+ * queue, or in transfer. Busy pages can't be discarded so they are not
+ * in LRU cache.
+ */
atomic_long_t cl_lru_busy;
+ /** # of LRU pages in the cache for this client_obd */
atomic_long_t cl_lru_in_list;
+ /** # of threads are shrinking LRU cache. To avoid contention, it's not
+ * allowed to have multiple threads shrinking LRU cache.
+ */
atomic_t cl_lru_shrinkers;
- struct list_head cl_lru_list; /* lru page list */
- spinlock_t cl_lru_list_lock; /* page list protector */
+ /** List of LRU pages for this client_obd */
+ struct list_head cl_lru_list;
+ /** Lock for LRU page list */
+ spinlock_t cl_lru_list_lock;
+ /** # of unstable pages in this client_obd.
+ * An unstable page is a page state that WRITE RPC has finished but
+ * the transaction has NOT yet committed.
+ */
atomic_long_t cl_unstable_count;

/* number of in flight destroy rpcs is limited to max_rpcs_in_flight */
diff --git a/drivers/staging/lustre/lustre/osc/osc_page.c b/drivers/staging/lustre/lustre/osc/osc_page.c
index 7a1f102..2cdc30a 100644
--- a/drivers/staging/lustre/lustre/osc/osc_page.c
+++ b/drivers/staging/lustre/lustre/osc/osc_page.c
@@ -343,16 +343,17 @@ void osc_page_submit(const struct lu_env *env, struct osc_page *opg,
* OSC to free slots voluntarily to maintain a reasonable number of free slots
* at any time.
*/
-
static DECLARE_WAIT_QUEUE_HEAD(osc_lru_waitq);
-/* LRU pages are freed in batch mode. OSC should at least free this
- * number of pages to avoid running out of LRU budget, and..
+
+/**
+ * LRU pages are freed in batch mode. OSC should at least free this
+ * number of pages to avoid running out of LRU slots.
*/
static const int lru_shrink_min = 2 << (20 - PAGE_SHIFT); /* 2M */
-/* free this number at most otherwise it will take too long time to finish. */
static const int lru_shrink_max = 8 << (20 - PAGE_SHIFT); /* 8M */

-/* Check if we can free LRU slots from this OSC. If there exists LRU waiters,
+/**
+ * Check if we can free LRU slots from this OSC. If there exists LRU waiters,
* we should free slots aggressively. In this way, slots are freed in a steady
* step to maintain fairness among OSCs.
*
@@ -643,6 +644,12 @@ long osc_lru_shrink(const struct lu_env *env, struct client_obd *cli,
return count > 0 ? count : rc;
}

+/**
+ * Reclaim LRU pages by an IO thread. The caller wants to reclaim at least
+ * \@npages of LRU slots. For performance consideration, it's better to drop
+ * LRU pages in batch. Therefore, the actual number is adjusted at least
+ * max_pages_per_rpc.
+ */
long osc_lru_reclaim(struct client_obd *cli)
{
struct lu_env *env;
--
1.7.1