答复: [????] Re: [PATCH v2] mm/vmalloc: use dedicated unbound workqueue for vmap area draining

Li,Rongqing(ACG CCN)
2026-03-19T10:08:54Z

> On Thu, Mar 19, 2026 at 03:43:07AM -0400, lirongqing wrote:
> > From: Li RongQing <lirongqing@baidu.com>
> >
> > The drain_vmap_area_work() function can take >10ms to complete when
> > there are many accumulated vmap areas in a system with a high CPU
> > count, causing workqueue watchdog warnings when run via
> > schedule_work():
> >
> > [ 2069.796205] workqueue: drain_vmap_area_work hogged CPU
> for >10000us
> > 4 times, consider switching to WQ_UNBOUND [ 2192.823225] workqueue:
> > drain_vmap_area_work hogged CPU for >10000us 5 times, consider
> > switching to WQ_UNBOUND
> >
> > Switch to a dedicated WQ_UNBOUND workqueue to allow the scheduler to
> > run this background task on any available CPU, improving responsiveness.
> > Use WQ_MEM_RECLAIM to ensure forward progress under memory
> pressure.
> >
> > Create vmap_drain_wq in vmalloc_init_late() which is called after
> > workqueue_init_early() in start_kernel() to avoid boot-time crashes.
> >
> > Suggested-by: Uladzislau Rezki <urezki@gmail.com>
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > ---
> > Diff with v1: create dedicated unbound workqueue
> >
> > include/linux/vmalloc.h | 2 ++
> > init/main.c | 1 +
> > mm/vmalloc.c | 14 +++++++++++++-
> > 3 files changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h index
> > e8e94f9..c028603 100644
> > --- a/include/linux/vmalloc.h
> > +++ b/include/linux/vmalloc.h
> > @@ -301,11 +301,13 @@ static inline void set_vm_flush_reset_perms(void
> *addr)
> > if (vm)
> > vm->flags |= VM_FLUSH_RESET_PERMS;
> > }
> > +void __init vmalloc_init_late(void);
> > #else /* !CONFIG_MMU */
> > #define VMALLOC_TOTAL 0UL
> >
> > static inline unsigned long vmalloc_nr_pages(void) { return 0; }
> > static inline void set_vm_flush_reset_perms(void *addr) {}
> > +static inline void __init vmalloc_init_late(void) {}
> > #endif /* CONFIG_MMU */
> >
> > #if defined(CONFIG_MMU) && defined(CONFIG_SMP) diff --git
> > a/init/main.c b/init/main.c index 1cb395d..50b497f 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -1099,6 +1099,7 @@ void start_kernel(void)
> > * workqueue_init().
> > */
> > workqueue_init_early();
> > + vmalloc_init_late();
> >
> No, no. We should not patch main.c for such purpose :)
>
> > rcu_init();
> > kvfree_rcu_init();
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 61caa55..a52ccd4 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -1067,6 +1067,7 @@ static void
> reclaim_and_purge_vmap_areas(void);
> > static BLOCKING_NOTIFIER_HEAD(vmap_notify_list);
> > static void drain_vmap_area_work(struct work_struct *work); static
> > DECLARE_WORK(drain_vmap_work, drain_vmap_area_work);
> > +static struct workqueue_struct *vmap_drain_wq;
> >
> > static __cacheline_aligned_in_smp atomic_long_t nr_vmalloc_pages;
> > static __cacheline_aligned_in_smp atomic_long_t vmap_lazy_nr; @@
> > -2471,7 +2472,7 @@ static void free_vmap_area_noflush(struct vmap_area
> > *va)
> >
> > /* After this point, we may free va at any time */
> > if (unlikely(nr_lazy > nr_lazy_max))
> > - schedule_work(&drain_vmap_work);
> > + queue_work(vmap_drain_wq, &drain_vmap_work);
> > }
> >
> > /*
> > @@ -5422,6 +5423,17 @@ vmap_node_shrink_scan(struct shrinker
> *shrink, struct shrink_control *sc)
> > return SHRINK_STOP;
> > }
> >
> > +void __init vmalloc_init_late(void)
> > +{
> > + vmap_drain_wq = alloc_workqueue("vmap_drain",
> > + WQ_UNBOUND | WQ_MEM_RECLAIM, 0);
> > + if (!vmap_drain_wq) {
> > + pr_warn("vmap_drain_wq creation failed, using
> system_unbound_wq\n");
> > + vmap_drain_wq = system_unbound_wq;
> > + }
> > +
> > +}
> > +
> > void __init vmalloc_init(void)
> > {
> > struct shrinker *vmap_node_shrinker;
> > --
> > 2.9.4
> >
> Why can't you add this into the vmalloc_ini()?
>

If alloc_workqueue() is added into vmalloc_ini(), system will crash and fail to boot, sine allocate workqueue depends on workqueue_init_early()

Maybe this commit 3347fa092821("workqueue: make workqueue available early during boot") shows the reason

[Li,Rongqing]

> --
> Uladzislau Rezki