[PATCH v2] md/r5cache: handle alloc_page failure

[Song Liu <songliubraving@fb.com>]

RMW of r5c write back cache uses an extra page to store old data for
prexor. handle_stripe_dirtying() allocates this page by calling
alloc_page(). However, alloc_page() may fail.

To handle alloc_page() failures, this patch adds a small mempool
in r5l_log. When alloc_page fails, handle_stripe() trys to use pages
from the mempool. When the mempool is in use, the stripe is added
to delayed_list.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 drivers/md/raid5.c       | 47 ++++++++++++++++++++++++++++++++++++++---------
 drivers/md/raid5.h       |  8 ++++++++
 3 files changed, 89 insertions(+), 9 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 8cb79fc..9406c39 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -162,6 +162,9 @@ struct r5l_log {
 
 	/* to submit async io_units, to fulfill ordering of flush */
 	struct work_struct deferred_io_work;
+
+	/* to handle alloc_page() failures in handle_stripe_dirtying() */
+	mempool_t *extra_page_pool;
 };
 
 /*
@@ -2334,15 +2337,48 @@ int r5c_try_caching_write(struct r5conf *conf,
  */
 void r5c_release_extra_page(struct stripe_head *sh)
 {
+	struct r5conf *conf = sh->raid_conf;
+	struct r5l_log *log = conf->log;
 	int i;
+	bool using_extra_page_pool;
+
+	using_extra_page_pool = test_and_clear_bit(
+		STRIPE_R5C_EXTRA_PAGE, &sh->state);
 
 	for (i = sh->disks; i--; )
 		if (sh->dev[i].page != sh->dev[i].orig_page) {
 			struct page *p = sh->dev[i].orig_page;
 
 			sh->dev[i].orig_page = sh->dev[i].page;
+			if (using_extra_page_pool)
+				mempool_free(p, log->extra_page_pool);
+			else
+				put_page(p);
+		}
+
+	if (using_extra_page_pool)
+		clear_bit(R5C_EXTRA_PAGE_IN_USE, &conf->cache_state);
+}
+
+void r5c_use_extra_page_pool(struct stripe_head *sh)
+{
+	struct r5l_log *log = sh->raid_conf->log;
+	int i;
+	struct r5dev *dev;
+	struct page *p;
+
+	for (i = sh->disks; i--; ) {
+		dev = &sh->dev[i];
+		if (dev->orig_page != dev->page) {
+			p = dev->orig_page;
+			dev->orig_page = dev->page;
 			put_page(p);
 		}
+		dev->orig_page = mempool_alloc(log->extra_page_pool,
+					       GFP_ATOMIC);
+		BUG_ON(!dev->orig_page);
+	}
+	set_bit(STRIPE_R5C_EXTRA_PAGE, &sh->state);
 }
 
 /*
@@ -2581,6 +2617,10 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 	if (!log->meta_pool)
 		goto out_mempool;
 
+	log->extra_page_pool = mempool_create_page_pool(conf->raid_disks, 0);
+	if (!log->extra_page_pool)
+		goto extra_page_pool;
+
 	log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
 						 log->rdev->mddev, "reclaim");
 	if (!log->reclaim_thread)
@@ -2611,6 +2651,8 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 error:
 	md_unregister_thread(&log->reclaim_thread);
 reclaim_thread:
+	mempool_destroy(log->extra_page_pool);
+extra_page_pool:
 	mempool_destroy(log->meta_pool);
 out_mempool:
 	bioset_free(log->bs);
@@ -2626,6 +2668,7 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 void r5l_exit_log(struct r5l_log *log)
 {
 	md_unregister_thread(&log->reclaim_thread);
+	mempool_destroy(log->extra_page_pool);
 	mempool_destroy(log->meta_pool);
 	bioset_free(log->bs);
 	mempool_destroy(log->io_pool);
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index dbab8c7..9d20849 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -876,6 +876,8 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
 
 	if (!test_bit(STRIPE_R5C_CACHING, &sh->state)) {
 		/* writing out phase */
+		if (s->waiting_extra_page)
+			return;
 		if (r5l_write_stripe(conf->log, sh) == 0)
 			return;
 	} else {  /* caching phase */
@@ -2007,6 +2009,7 @@ static struct stripe_head *alloc_stripe(struct kmem_cache *sc, gfp_t gfp,
 		INIT_LIST_HEAD(&sh->batch_list);
 		INIT_LIST_HEAD(&sh->lru);
 		INIT_LIST_HEAD(&sh->r5c);
+		INIT_LIST_HEAD(&sh->log_list);
 		atomic_set(&sh->count, 1);
 		sh->log_start = MaxSector;
 		for (i = 0; i < disks; i++) {
@@ -3580,10 +3583,10 @@ static void handle_stripe_clean_event(struct r5conf *conf,
 		break_stripe_batch_list(head_sh, STRIPE_EXPAND_SYNC_FLAGS);
 }
 
-static void handle_stripe_dirtying(struct r5conf *conf,
-				   struct stripe_head *sh,
-				   struct stripe_head_state *s,
-				   int disks)
+static int handle_stripe_dirtying(struct r5conf *conf,
+				  struct stripe_head *sh,
+				  struct stripe_head_state *s,
+				  int disks)
 {
 	int rmw = 0, rcw = 0, i;
 	sector_t recovery_cp = conf->mddev->recovery_cp;
@@ -3649,12 +3652,32 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 			    dev->page == dev->orig_page &&
 			    !test_bit(R5_LOCKED, &sh->dev[sh->pd_idx].flags)) {
 				/* alloc page for prexor */
-				dev->orig_page = alloc_page(GFP_NOIO);
+				struct page *p = alloc_page(GFP_NOIO);
+
+				if (p) {
+					dev->orig_page = p;
+					continue;
+				}
 
-				/* will handle failure in a later patch*/
-				BUG_ON(!dev->orig_page);
+				/*
+				 * alloc_page() failed, try use
+				 * log->extra_page_pool
+				 */
+				if (!test_and_set_bit(R5C_EXTRA_PAGE_IN_USE,
+						      &conf->cache_state)) {
+					r5c_use_extra_page_pool(sh);
+					break;
+				}
+
+				/* extra_page_pool busy, add to delayed_list */
+				set_bit(STRIPE_DELAYED, &sh->state);
+				s->waiting_extra_page = 1;
+				return -EAGAIN;
 			}
+		}
 
+		for (i = disks; i--; ) {
+			struct r5dev *dev = &sh->dev[i];
 			if ((dev->towrite ||
 			     i == sh->pd_idx || i == sh->qd_idx ||
 			     test_bit(R5_InJournal, &dev->flags)) &&
@@ -3730,6 +3753,7 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 	    (s->locked == 0 && (rcw == 0 || rmw == 0) &&
 	     !test_bit(STRIPE_BIT_DELAY, &sh->state)))
 		schedule_reconstruction(sh, s, rcw == 0, 0);
+	return 0;
 }
 
 static void handle_parity_checks5(struct r5conf *conf, struct stripe_head *sh,
@@ -4545,8 +4569,12 @@ static void handle_stripe(struct stripe_head *sh)
 			if (ret == -EAGAIN ||
 			    /* stripe under reclaim: !caching && injournal */
 			    (!test_bit(STRIPE_R5C_CACHING, &sh->state) &&
-			     s.injournal > 0))
-				handle_stripe_dirtying(conf, sh, &s, disks);
+			     s.injournal > 0)) {
+				ret = handle_stripe_dirtying(conf, sh, &s,
+							     disks);
+				if (ret == -EAGAIN)
+					goto finish;
+			}
 		}
 	}
 
@@ -6612,6 +6640,7 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 
 	conf->disks = kzalloc(max_disks * sizeof(struct disk_info),
 			      GFP_KERNEL);
+
 	if (!conf->disks)
 		goto abort;
 
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index d13fe45..fad19eb 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -276,6 +276,7 @@ struct stripe_head_state {
 	struct md_rdev *blocked_rdev;
 	int handle_bad_blocks;
 	int log_failed;
+	int waiting_extra_page;
 };
 
 /* Flags for struct r5dev.flags */
@@ -377,6 +378,9 @@ enum {
 				 * in conf->r5c_full_stripe_list)
 				 */
 	STRIPE_R5C_PREFLUSH,	/* need to flush journal device */
+	STRIPE_R5C_EXTRA_PAGE,	/* extra orig_page of this stripe is allocated
+				 * from extra_page_pool
+				 */
 };
 
 #define STRIPE_EXPAND_SYNC_FLAGS \
@@ -559,6 +563,9 @@ enum r5_cache_state {
 				 * only process stripes that are already
 				 * occupying the log
 				 */
+	R5C_EXTRA_PAGE_IN_USE,	/* a stripe is using the pages in
+				 * r5l_log.extra_page_pool for prexor
+				 */
 };
 
 struct r5conf {
@@ -765,6 +772,7 @@ extern void
 r5c_finish_stripe_write_out(struct r5conf *conf, struct stripe_head *sh,
 			    struct stripe_head_state *s);
 extern void r5c_release_extra_page(struct stripe_head *sh);
+extern void r5c_use_extra_page_pool(struct stripe_head *sh);
 extern void r5l_wake_reclaim(struct r5l_log *log, sector_t space);
 extern void r5c_handle_cached_data_endio(struct r5conf *conf,
 	struct stripe_head *sh, int disks, struct bio_list *return_bi);
-- 
2.9.3