| Message ID | 20160929110714.GF28107@nuc-i3427.alporthouse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 29 Sep 2016 12:07:14 +0100 Chris Wilson wrote: > On Thu, Sep 29, 2016 at 04:28:08PM +0800, Jisheng Zhang wrote: > > On Thu, 29 Sep 2016 09:18:18 +0100 Chris Wilson wrote: > > > > > On Thu, Sep 29, 2016 at 03:34:11PM +0800, Jisheng Zhang wrote: > > > > On Marvell berlin arm64 platforms, I see the preemptoff tracer report > > > > a max 26543 us latency at __purge_vmap_area_lazy, this latency is an > > > > awfully bad for STB. And the ftrace log also shows __free_vmap_area > > > > contributes most latency now. I noticed that Joel mentioned the same > > > > issue[1] on x86 platform and gave two solutions, but it seems no patch > > > > is sent out for this purpose. > > > > > > > > This patch adopts Joel's first solution, but I use 16MB per core > > > > rather than 8MB per core for the number of lazy_max_pages. After this > > > > patch, the preemptoff tracer reports a max 6455us latency, reduced to > > > > 1/4 of original result. > > > > > > My understanding is that > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > index 91f44e78c516..3f7c6d6969ac 100644 > > > --- a/mm/vmalloc.c > > > +++ b/mm/vmalloc.c > > > @@ -626,7 +626,6 @@ void set_iounmap_nonlazy(void) > > > static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, > > > int sync, int force_flush) > > > { > > > - static DEFINE_SPINLOCK(purge_lock); > > > struct llist_node *valist; > > > struct vmap_area *va; > > > struct vmap_area *n_va; > > > @@ -637,12 +636,6 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, > > > * should not expect such behaviour. This just simplifies locking for > > > * the case that isn't actually used at the moment anyway. > > > */ > > > - if (!sync && !force_flush) { > > > - if (!spin_trylock(&purge_lock)) > > > - return; > > > - } else > > > - spin_lock(&purge_lock); > > > - > > > if (sync) > > > purge_fragmented_blocks_allcpus(); > > > > > > @@ -667,7 +660,6 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, > > > __free_vmap_area(va); > > > spin_unlock(&vmap_area_lock); > > > > Hi Chris, > > > > Per my test, the bottleneck now is __free_vmap_area() over the valist, the > > iteration is protected with spinlock vmap_area_lock. So the larger lazy max > > pages, the longer valist, the bigger the latency. > > > > So besides above patch, we still need to remove vmap_are_lock or replace with > > mutex. > > Or follow up with > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 3f7c6d6969ac..67b5475f0b0a 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -656,8 +656,10 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, > > if (nr) { > spin_lock(&vmap_area_lock); > - llist_for_each_entry_safe(va, n_va, valist, purge_list) > + llist_for_each_entry_safe(va, n_va, valist, purge_list) { > __free_vmap_area(va); > + cond_resched_lock(&vmap_area_lock); oh, great! This seems works fine. I'm not sure there's any side effect or performance regression, but this patch plus previous purge_lock removing do addressed my problem. Thanks, Jisheng > + } > spin_unlock(&vmap_area_lock); > } > } > > ? > -Chris >
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 3f7c6d6969ac..67b5475f0b0a 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -656,8 +656,10 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, if (nr) { spin_lock(&vmap_area_lock); - llist_for_each_entry_safe(va, n_va, valist, purge_list) + llist_for_each_entry_safe(va, n_va, valist, purge_list) { __free_vmap_area(va); + cond_resched_lock(&vmap_area_lock); + } spin_unlock(&vmap_area_lock); } }