| Message ID | 20211021124441.668816-6-hch@lst.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/5] mm: export bdi_unregister | expand |
On Thu 21-10-21 14:44:41, Christoph Hellwig wrote: > Move grabbing and releasing the bdi refcount out of the common > wb_init/wb_exit helpers into code that is only used for the non-default > memcg driven bdi_writeback structures. > > Signed-off-by: Christoph Hellwig <hch@lst.de> Can we perhaps add a comment to struct bdi_writeback definition (or maybe wb_init()?) mentioning that it holds a reference to 'bdi' if it is bdi_writeback struct for a cgroup? I don't see it mentioned anywhere and now that you've changed the code, it isn't that obvious from the code either... Otherwise the patch looks good so feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > mm/backing-dev.c | 13 +++++-------- > 1 file changed, 5 insertions(+), 8 deletions(-) > > diff --git a/mm/backing-dev.c b/mm/backing-dev.c > index 768e9ae489f66..5ccb250898083 100644 > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -291,8 +291,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi, > > memset(wb, 0, sizeof(*wb)); > > - if (wb != &bdi->wb) > - bdi_get(bdi); > wb->bdi = bdi; > wb->last_old_flush = jiffies; > INIT_LIST_HEAD(&wb->b_dirty); > @@ -316,7 +314,7 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi, > > err = fprop_local_init_percpu(&wb->completions, gfp); > if (err) > - goto out_put_bdi; > + return err; > > for (i = 0; i < NR_WB_STAT_ITEMS; i++) { > err = percpu_counter_init(&wb->stat[i], 0, gfp); > @@ -330,9 +328,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi, > while (i--) > percpu_counter_destroy(&wb->stat[i]); > fprop_local_destroy_percpu(&wb->completions); > -out_put_bdi: > - if (wb != &bdi->wb) > - bdi_put(bdi); > return err; > } > > @@ -373,8 +368,6 @@ static void wb_exit(struct bdi_writeback *wb) > percpu_counter_destroy(&wb->stat[i]); > > fprop_local_destroy_percpu(&wb->completions); > - if (wb != &wb->bdi->wb) > - bdi_put(wb->bdi); > } > > #ifdef CONFIG_CGROUP_WRITEBACK > @@ -397,6 +390,7 @@ static void cgwb_release_workfn(struct work_struct *work) > struct bdi_writeback *wb = container_of(work, struct bdi_writeback, > release_work); > struct blkcg *blkcg = css_to_blkcg(wb->blkcg_css); > + struct backing_dev_info *bdi = wb->bdi; > > mutex_lock(&wb->bdi->cgwb_release_mutex); > wb_shutdown(wb); > @@ -416,6 +410,7 @@ static void cgwb_release_workfn(struct work_struct *work) > > percpu_ref_exit(&wb->refcnt); > wb_exit(wb); > + bdi_put(bdi); > WARN_ON_ONCE(!list_empty(&wb->b_attached)); > kfree_rcu(wb, rcu); > } > @@ -497,6 +492,7 @@ static int cgwb_create(struct backing_dev_info *bdi, > INIT_LIST_HEAD(&wb->b_attached); > INIT_WORK(&wb->release_work, cgwb_release_workfn); > set_bit(WB_registered, &wb->state); > + bdi_get(bdi); > > /* > * The root wb determines the registered state of the whole bdi and > @@ -528,6 +524,7 @@ static int cgwb_create(struct backing_dev_info *bdi, > goto out_put; > > err_fprop_exit: > + bdi_put(bdi); > fprop_local_destroy_percpu(&wb->memcg_completions); > err_ref_exit: > percpu_ref_exit(&wb->refcnt); > -- > 2.30.2 >
On Fri, Oct 22, 2021 at 11:02:03AM +0200, Jan Kara wrote: > On Thu 21-10-21 14:44:41, Christoph Hellwig wrote: > > Move grabbing and releasing the bdi refcount out of the common > > wb_init/wb_exit helpers into code that is only used for the non-default > > memcg driven bdi_writeback structures. > > > > Signed-off-by: Christoph Hellwig <hch@lst.de> > > Can we perhaps add a comment to struct bdi_writeback definition (or maybe > wb_init()?) mentioning that it holds a reference to 'bdi' if it is > bdi_writeback struct for a cgroup? I don't see it mentioned anywhere and > now that you've changed the code, it isn't that obvious from the code > either... Otherwise the patch looks good so feel free to add: Like this? diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index 33207004cfded..a3d7dd1cc30a1 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -103,6 +103,9 @@ struct wb_completion { * change as blkcg is disabled and enabled higher up in the hierarchy, a wb * is tested for blkcg after lookup and removed from index on mismatch so * that a new wb for the combination can be created. + * + * Each bdi_writeback that is no embedded into the backing_dev_info must hold + * a reference to the parent backing_dev_info. See cgwb_create() for details. */ struct bdi_writeback { struct backing_dev_info *bdi; /* our parent bdi */
On Wed 27-10-21 09:42:07, Christoph Hellwig wrote: > On Fri, Oct 22, 2021 at 11:02:03AM +0200, Jan Kara wrote: > > On Thu 21-10-21 14:44:41, Christoph Hellwig wrote: > > > Move grabbing and releasing the bdi refcount out of the common > > > wb_init/wb_exit helpers into code that is only used for the non-default > > > memcg driven bdi_writeback structures. > > > > > > Signed-off-by: Christoph Hellwig <hch@lst.de> > > > > Can we perhaps add a comment to struct bdi_writeback definition (or maybe > > wb_init()?) mentioning that it holds a reference to 'bdi' if it is > > bdi_writeback struct for a cgroup? I don't see it mentioned anywhere and > > now that you've changed the code, it isn't that obvious from the code > > either... Otherwise the patch looks good so feel free to add: > > Like this? > > diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h > index 33207004cfded..a3d7dd1cc30a1 100644 > --- a/include/linux/backing-dev-defs.h > +++ b/include/linux/backing-dev-defs.h > @@ -103,6 +103,9 @@ struct wb_completion { > * change as blkcg is disabled and enabled higher up in the hierarchy, a wb > * is tested for blkcg after lookup and removed from index on mismatch so > * that a new wb for the combination can be created. > + * > + * Each bdi_writeback that is no embedded into the backing_dev_info must hold ^^^ not > + * a reference to the parent backing_dev_info. See cgwb_create() for details. > */ Otherwise looks nice. Thanks! Honza
diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 768e9ae489f66..5ccb250898083 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -291,8 +291,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi, memset(wb, 0, sizeof(*wb)); - if (wb != &bdi->wb) - bdi_get(bdi); wb->bdi = bdi; wb->last_old_flush = jiffies; INIT_LIST_HEAD(&wb->b_dirty); @@ -316,7 +314,7 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi, err = fprop_local_init_percpu(&wb->completions, gfp); if (err) - goto out_put_bdi; + return err; for (i = 0; i < NR_WB_STAT_ITEMS; i++) { err = percpu_counter_init(&wb->stat[i], 0, gfp); @@ -330,9 +328,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi, while (i--) percpu_counter_destroy(&wb->stat[i]); fprop_local_destroy_percpu(&wb->completions); -out_put_bdi: - if (wb != &bdi->wb) - bdi_put(bdi); return err; } @@ -373,8 +368,6 @@ static void wb_exit(struct bdi_writeback *wb) percpu_counter_destroy(&wb->stat[i]); fprop_local_destroy_percpu(&wb->completions); - if (wb != &wb->bdi->wb) - bdi_put(wb->bdi); } #ifdef CONFIG_CGROUP_WRITEBACK @@ -397,6 +390,7 @@ static void cgwb_release_workfn(struct work_struct *work) struct bdi_writeback *wb = container_of(work, struct bdi_writeback, release_work); struct blkcg *blkcg = css_to_blkcg(wb->blkcg_css); + struct backing_dev_info *bdi = wb->bdi; mutex_lock(&wb->bdi->cgwb_release_mutex); wb_shutdown(wb); @@ -416,6 +410,7 @@ static void cgwb_release_workfn(struct work_struct *work) percpu_ref_exit(&wb->refcnt); wb_exit(wb); + bdi_put(bdi); WARN_ON_ONCE(!list_empty(&wb->b_attached)); kfree_rcu(wb, rcu); } @@ -497,6 +492,7 @@ static int cgwb_create(struct backing_dev_info *bdi, INIT_LIST_HEAD(&wb->b_attached); INIT_WORK(&wb->release_work, cgwb_release_workfn); set_bit(WB_registered, &wb->state); + bdi_get(bdi); /* * The root wb determines the registered state of the whole bdi and @@ -528,6 +524,7 @@ static int cgwb_create(struct backing_dev_info *bdi, goto out_put; err_fprop_exit: + bdi_put(bdi); fprop_local_destroy_percpu(&wb->memcg_completions); err_ref_exit: percpu_ref_exit(&wb->refcnt);
Move grabbing and releasing the bdi refcount out of the common wb_init/wb_exit helpers into code that is only used for the non-default memcg driven bdi_writeback structures. Signed-off-by: Christoph Hellwig <hch@lst.de> --- mm/backing-dev.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-)