blkcg, cfq-iosched: use GFP_NOWAIT instead of GFP_ATOMIC for non-critical allocations

blkcg performs several allocations to track IOs per cgroup and enforce
resource control.  Most of these allocations are performed lazily on
demand in the IO path and thus can't involve reclaim path.  Currently,
these allocations use GFP_ATOMIC; however, blkcg can gracefully deal
with occassional failures of these allocations by punting IOs to the
root cgroup and there's no reason to reach into the emergency reserve.

This patch replaces GFP_ATOMIC with GFP_NOWAIT for the following
allocations.

* bdi_writeback_congested and blkcg_gq allocations in blkg_create().

* radix tree node allocations for blkcg->blkg_tree.

* cfq_queue allocation on ioprio changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-and-Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Suggested-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index d6283b3f5db50674d18ae485970f1e24ed44569d..1db904f955023f5783810bf6966022f462038625 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -188,7 +188,7 @@ EXPORT_SYMBOL_GPL(blkg_lookup);
 
 /*
  * If @new_blkg is %NULL, this function tries to allocate a new one as
- * necessary using %GFP_ATOMIC.  @new_blkg is always consumed on return.
+ * necessary using %GFP_NOWAIT.  @new_blkg is always consumed on return.
  */
 static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
                                    struct request_queue *q,
@@ -208,7 +208,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
        }
 
        wb_congested = wb_congested_get_create(&q->backing_dev_info,
-                                              blkcg->css.id, GFP_ATOMIC);
+                                              blkcg->css.id, GFP_NOWAIT);
        if (!wb_congested) {
                ret = -ENOMEM;
                goto err_put_css;
@@ -216,7 +216,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
 
        /* allocate */
        if (!new_blkg) {
-               new_blkg = blkg_alloc(blkcg, q, GFP_ATOMIC);
+               new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT);
                if (unlikely(!new_blkg)) {
                        ret = -ENOMEM;
                        goto err_put_congested;
@@ -882,7 +882,7 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
 
 done:
        spin_lock_init(&blkcg->lock);
-       INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);
+       INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT);
        INIT_HLIST_HEAD(&blkcg->blkg_list);
 #ifdef CONFIG_CGROUP_WRITEBACK
        INIT_LIST_HEAD(&blkcg->cgwb_list);

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index bf6f49cca311e83900cee6d61f4b0bfbc2fdca71..5f119292a254abf6bb4cde3722768a2f2fa63140 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3575,7 +3575,7 @@ static void check_ioprio_changed(struct cfq_io_cq *cic, struct bio *bio)
        cfqq = cic_to_cfqq(cic, false);
        if (cfqq) {
                cfq_put_queue(cfqq);
-               cfqq = cfq_get_queue(cfqd, BLK_RW_ASYNC, cic, bio, GFP_ATOMIC);
+               cfqq = cfq_get_queue(cfqd, BLK_RW_ASYNC, cic, bio, GFP_NOWAIT);
                cic_set_cfqq(cic, cfqq, false);
        }