| Message ID | 20230323040037.2389095-4-yosryahmed@google.com (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
| Series | Make rstat flushing IRQ and sleep friendly | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Thu, Mar 23, 2023 at 04:00:33AM +0000, Yosry Ahmed wrote: > The naming of cgroup_rstat_flush_irqsafe() can be confusing. > It can read like "irqsave", which means that it disables > interrupts throughout, but it actually doesn't. It is just "safe" to > call from contexts with interrupts disabled. > > Furthermore, this is only used today by mem_cgroup_flush_stats(), which > will be changed by a later patch to optionally allow sleeping. Simplify > the code and make it easier to reason about by instead passing in an > explicit @may_sleep argument to cgroup_rstat_flush(), which gets passed > directly to cgroup_rstat_flush_locked(). > > Signed-off-by: Yosry Ahmed <yosryahmed@google.com> > --- > block/blk-cgroup.c | 2 +- > include/linux/cgroup.h | 3 +-- > kernel/cgroup/cgroup.c | 4 ++-- > kernel/cgroup/rstat.c | 24 +++++------------------- > mm/memcontrol.c | 6 +++--- > 5 files changed, 12 insertions(+), 27 deletions(-) > > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c > index bd50b55bdb61..3fe313ce5e6b 100644 > --- a/block/blk-cgroup.c > +++ b/block/blk-cgroup.c > @@ -1043,7 +1043,7 @@ static int blkcg_print_stat(struct seq_file *sf, void *v) > if (!seq_css(sf)->parent) > blkcg_fill_root_iostats(); > else > - cgroup_rstat_flush(blkcg->css.cgroup); > + cgroup_rstat_flush(blkcg->css.cgroup, true); > > rcu_read_lock(); > hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) { > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > index 3410aecffdb4..743c345b6a3f 100644 > --- a/include/linux/cgroup.h > +++ b/include/linux/cgroup.h > @@ -691,8 +691,7 @@ static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen) > * cgroup scalable recursive statistics. > */ > void cgroup_rstat_updated(struct cgroup *cgrp, int cpu); > -void cgroup_rstat_flush(struct cgroup *cgrp); > -void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp); > +void cgroup_rstat_flush(struct cgroup *cgrp, bool may_sleep); > void cgroup_rstat_flush_hold(struct cgroup *cgrp); > void cgroup_rstat_flush_release(void); > > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index 935e8121b21e..58df0fc379f6 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -5393,7 +5393,7 @@ static void css_release_work_fn(struct work_struct *work) > if (ss) { > /* css release path */ > if (!list_empty(&css->rstat_css_node)) { > - cgroup_rstat_flush(cgrp); > + cgroup_rstat_flush(cgrp, true); > list_del_rcu(&css->rstat_css_node); > } > > @@ -5406,7 +5406,7 @@ static void css_release_work_fn(struct work_struct *work) > /* cgroup release path */ > TRACE_CGROUP_PATH(release, cgrp); > > - cgroup_rstat_flush(cgrp); > + cgroup_rstat_flush(cgrp, true); This is an anti-pattern, please don't do this. Naked bool arguments are a pain to comprehend at the callsite and an easy vector for bugs. cgroup_rstat_flush_atomic() would be a better name for, well, atomic callsites. > diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c > index af11e28bd055..fe8690bb1e1c 100644 > --- a/kernel/cgroup/rstat.c > +++ b/kernel/cgroup/rstat.c > @@ -243,30 +243,16 @@ static bool should_skip_flush(void) > * This function is safe to call from contexts that disable interrupts, but > * @may_sleep must be set to false, otherwise the function may block. > */ > -__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp) > +__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp, bool may_sleep) > { > if (should_skip_flush()) > return; > > - might_sleep(); > - spin_lock(&cgroup_rstat_lock); > - cgroup_rstat_flush_locked(cgrp, true); > - spin_unlock(&cgroup_rstat_lock); > -} > - > -/** > - * cgroup_rstat_flush_irqsafe - irqsafe version of cgroup_rstat_flush() > - * @cgrp: target cgroup > - * > - * This function can be called from any context. > - */ > -void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp) > -{ > - if (should_skip_flush()) > - return; > + if (may_sleep) > + might_sleep(); might_sleep_if()
On Thu, Mar 23, 2023 at 8:43 AM Johannes Weiner <hannes@cmpxchg.org> wrote: > > On Thu, Mar 23, 2023 at 04:00:33AM +0000, Yosry Ahmed wrote: > > The naming of cgroup_rstat_flush_irqsafe() can be confusing. > > It can read like "irqsave", which means that it disables > > interrupts throughout, but it actually doesn't. It is just "safe" to > > call from contexts with interrupts disabled. > > > > Furthermore, this is only used today by mem_cgroup_flush_stats(), which > > will be changed by a later patch to optionally allow sleeping. Simplify > > the code and make it easier to reason about by instead passing in an > > explicit @may_sleep argument to cgroup_rstat_flush(), which gets passed > > directly to cgroup_rstat_flush_locked(). > > > > Signed-off-by: Yosry Ahmed <yosryahmed@google.com> > > --- > > block/blk-cgroup.c | 2 +- > > include/linux/cgroup.h | 3 +-- > > kernel/cgroup/cgroup.c | 4 ++-- > > kernel/cgroup/rstat.c | 24 +++++------------------- > > mm/memcontrol.c | 6 +++--- > > 5 files changed, 12 insertions(+), 27 deletions(-) > > > > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c > > index bd50b55bdb61..3fe313ce5e6b 100644 > > --- a/block/blk-cgroup.c > > +++ b/block/blk-cgroup.c > > @@ -1043,7 +1043,7 @@ static int blkcg_print_stat(struct seq_file *sf, void *v) > > if (!seq_css(sf)->parent) > > blkcg_fill_root_iostats(); > > else > > - cgroup_rstat_flush(blkcg->css.cgroup); > > + cgroup_rstat_flush(blkcg->css.cgroup, true); > > > > rcu_read_lock(); > > hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) { > > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > > index 3410aecffdb4..743c345b6a3f 100644 > > --- a/include/linux/cgroup.h > > +++ b/include/linux/cgroup.h > > @@ -691,8 +691,7 @@ static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen) > > * cgroup scalable recursive statistics. > > */ > > void cgroup_rstat_updated(struct cgroup *cgrp, int cpu); > > -void cgroup_rstat_flush(struct cgroup *cgrp); > > -void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp); > > +void cgroup_rstat_flush(struct cgroup *cgrp, bool may_sleep); > > void cgroup_rstat_flush_hold(struct cgroup *cgrp); > > void cgroup_rstat_flush_release(void); > > > > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > > index 935e8121b21e..58df0fc379f6 100644 > > --- a/kernel/cgroup/cgroup.c > > +++ b/kernel/cgroup/cgroup.c > > @@ -5393,7 +5393,7 @@ static void css_release_work_fn(struct work_struct *work) > > if (ss) { > > /* css release path */ > > if (!list_empty(&css->rstat_css_node)) { > > - cgroup_rstat_flush(cgrp); > > + cgroup_rstat_flush(cgrp, true); > > list_del_rcu(&css->rstat_css_node); > > } > > > > @@ -5406,7 +5406,7 @@ static void css_release_work_fn(struct work_struct *work) > > /* cgroup release path */ > > TRACE_CGROUP_PATH(release, cgrp); > > > > - cgroup_rstat_flush(cgrp); > > + cgroup_rstat_flush(cgrp, true); > > This is an anti-pattern, please don't do this. Naked bool arguments > are a pain to comprehend at the callsite and an easy vector for bugs. > > cgroup_rstat_flush_atomic() would be a better name for, well, atomic > callsites. Thanks for pointing this out. I will rename it to cgroup_rstat_flush_atomic() in upcoming versions instead. I will also do the same for mem_cgroup_flush_stats() as I introduce a similar boolean argument for it in the following patch. > > > diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c > > index af11e28bd055..fe8690bb1e1c 100644 > > --- a/kernel/cgroup/rstat.c > > +++ b/kernel/cgroup/rstat.c > > @@ -243,30 +243,16 @@ static bool should_skip_flush(void) > > * This function is safe to call from contexts that disable interrupts, but > > * @may_sleep must be set to false, otherwise the function may block. > > */ > > -__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp) > > +__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp, bool may_sleep) > > { > > if (should_skip_flush()) > > return; > > > > - might_sleep(); > > - spin_lock(&cgroup_rstat_lock); > > - cgroup_rstat_flush_locked(cgrp, true); > > - spin_unlock(&cgroup_rstat_lock); > > -} > > - > > -/** > > - * cgroup_rstat_flush_irqsafe - irqsafe version of cgroup_rstat_flush() > > - * @cgrp: target cgroup > > - * > > - * This function can be called from any context. > > - */ > > -void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp) > > -{ > > - if (should_skip_flush()) > > - return; > > + if (may_sleep) > > + might_sleep(); > > might_sleep_if() Thanks for pointing this out. I don't think it will be needed if we keep cgroup_rstat_flush_irqsafe() and only rename it to cgroup_rstat_flush_atomic(), but it is useful to know that it exists for future reference.
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index bd50b55bdb61..3fe313ce5e6b 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1043,7 +1043,7 @@ static int blkcg_print_stat(struct seq_file *sf, void *v) if (!seq_css(sf)->parent) blkcg_fill_root_iostats(); else - cgroup_rstat_flush(blkcg->css.cgroup); + cgroup_rstat_flush(blkcg->css.cgroup, true); rcu_read_lock(); hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) { diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 3410aecffdb4..743c345b6a3f 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -691,8 +691,7 @@ static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen) * cgroup scalable recursive statistics. */ void cgroup_rstat_updated(struct cgroup *cgrp, int cpu); -void cgroup_rstat_flush(struct cgroup *cgrp); -void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp); +void cgroup_rstat_flush(struct cgroup *cgrp, bool may_sleep); void cgroup_rstat_flush_hold(struct cgroup *cgrp); void cgroup_rstat_flush_release(void); diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 935e8121b21e..58df0fc379f6 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -5393,7 +5393,7 @@ static void css_release_work_fn(struct work_struct *work) if (ss) { /* css release path */ if (!list_empty(&css->rstat_css_node)) { - cgroup_rstat_flush(cgrp); + cgroup_rstat_flush(cgrp, true); list_del_rcu(&css->rstat_css_node); } @@ -5406,7 +5406,7 @@ static void css_release_work_fn(struct work_struct *work) /* cgroup release path */ TRACE_CGROUP_PATH(release, cgrp); - cgroup_rstat_flush(cgrp); + cgroup_rstat_flush(cgrp, true); spin_lock_irq(&css_set_lock); for (tcgrp = cgroup_parent(cgrp); tcgrp; diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index af11e28bd055..fe8690bb1e1c 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -243,30 +243,16 @@ static bool should_skip_flush(void) * This function is safe to call from contexts that disable interrupts, but * @may_sleep must be set to false, otherwise the function may block. */ -__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp) +__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp, bool may_sleep) { if (should_skip_flush()) return; - might_sleep(); - spin_lock(&cgroup_rstat_lock); - cgroup_rstat_flush_locked(cgrp, true); - spin_unlock(&cgroup_rstat_lock); -} - -/** - * cgroup_rstat_flush_irqsafe - irqsafe version of cgroup_rstat_flush() - * @cgrp: target cgroup - * - * This function can be called from any context. - */ -void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp) -{ - if (should_skip_flush()) - return; + if (may_sleep) + might_sleep(); spin_lock(&cgroup_rstat_lock); - cgroup_rstat_flush_locked(cgrp, false); + cgroup_rstat_flush_locked(cgrp, may_sleep); spin_unlock(&cgroup_rstat_lock); } @@ -325,7 +311,7 @@ void cgroup_rstat_exit(struct cgroup *cgrp) { int cpu; - cgroup_rstat_flush(cgrp); + cgroup_rstat_flush(cgrp, true); /* sanity check */ for_each_possible_cpu(cpu) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e0e92b38fa51..72cd44f88d97 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -644,7 +644,7 @@ static void __mem_cgroup_flush_stats(void) return; flush_next_time = jiffies_64 + 2*FLUSH_TIME; - cgroup_rstat_flush_irqsafe(root_mem_cgroup->css.cgroup); + cgroup_rstat_flush(root_mem_cgroup->css.cgroup, false); atomic_set(&stats_flush_threshold, 0); spin_unlock(&stats_flush_lock); } @@ -7745,7 +7745,7 @@ bool obj_cgroup_may_zswap(struct obj_cgroup *objcg) break; } - cgroup_rstat_flush(memcg->css.cgroup); + cgroup_rstat_flush(memcg->css.cgroup, true); pages = memcg_page_state(memcg, MEMCG_ZSWAP_B) / PAGE_SIZE; if (pages < max) continue; @@ -7810,7 +7810,7 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size) static u64 zswap_current_read(struct cgroup_subsys_state *css, struct cftype *cft) { - cgroup_rstat_flush(css->cgroup); + cgroup_rstat_flush(css->cgroup, true); return memcg_page_state(mem_cgroup_from_css(css), MEMCG_ZSWAP_B); }
The naming of cgroup_rstat_flush_irqsafe() can be confusing. It can read like "irqsave", which means that it disables interrupts throughout, but it actually doesn't. It is just "safe" to call from contexts with interrupts disabled. Furthermore, this is only used today by mem_cgroup_flush_stats(), which will be changed by a later patch to optionally allow sleeping. Simplify the code and make it easier to reason about by instead passing in an explicit @may_sleep argument to cgroup_rstat_flush(), which gets passed directly to cgroup_rstat_flush_locked(). Signed-off-by: Yosry Ahmed <yosryahmed@google.com> --- block/blk-cgroup.c | 2 +- include/linux/cgroup.h | 3 +-- kernel/cgroup/cgroup.c | 4 ++-- kernel/cgroup/rstat.c | 24 +++++------------------- mm/memcontrol.c | 6 +++--- 5 files changed, 12 insertions(+), 27 deletions(-)