kernel test robot reported the regression of fio.write_iops[1]
with [2].
Since lru_add_drain is called frequently, invalidate bh_lrus
there could increase bh_lrus cache miss ratio, which needs
more IO in the end.
This patch moves the bh_lrus invalidation from the hot path(
e.g., zap_page_range, pagevec_release) to cold path(i.e.,
lru_add_drain_all, lru_cache_disable).
[1] https://lore.kernel.org/lkml/20210520083144.GD14190@xsang-OptiPlex-9020/
[2] 8cc621d2f45d, mm: fs: invalidate BH LRU during page migration
Cc: "Xing, Zhengjun" <[email protected]>
Reported-by: kernel test robot <[email protected]>
Reviewed-by: Chris Goldsworthy <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
---
* from v1 - https://lore.kernel.org/lkml/[email protected]/
* add Reviewed-by - cgoldswo
mm/swap.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c
index 1958d5feb148..3e25d99a9dbb 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -642,7 +642,6 @@ void lru_add_drain_cpu(int cpu)
pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
activate_page_drain(cpu);
- invalidate_bh_lrus_cpu(cpu);
}
/**
@@ -725,6 +724,17 @@ void lru_add_drain(void)
local_unlock(&lru_pvecs.lock);
}
+static void lru_add_and_bh_lrus_drain(void)
+{
+ int cpu;
+
+ local_lock(&lru_pvecs.lock);
+ cpu = smp_processor_id();
+ lru_add_drain_cpu(cpu);
+ local_unlock(&lru_pvecs.lock);
+ invalidate_bh_lrus_cpu(cpu);
+}
+
void lru_add_drain_cpu_zone(struct zone *zone)
{
local_lock(&lru_pvecs.lock);
@@ -739,7 +749,7 @@ static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
static void lru_add_drain_per_cpu(struct work_struct *dummy)
{
- lru_add_drain();
+ lru_add_and_bh_lrus_drain();
}
/*
@@ -880,7 +890,7 @@ void lru_cache_disable(void)
*/
__lru_add_drain_all(true);
#else
- lru_add_drain();
+ lru_add_and_bh_lrus_drain();
#endif
}
--
2.31.1.818.g46aad6cb9e-goog
On Tue, 1 Jun 2021 07:54:25 -0700 Minchan Kim <[email protected]> wrote:
> kernel test robot reported the regression of fio.write_iops[1]
> with [2].
>
> Since lru_add_drain is called frequently, invalidate bh_lrus
> there could increase bh_lrus cache miss ratio, which needs
> more IO in the end.
>
> This patch moves the bh_lrus invalidation from the hot path(
> e.g., zap_page_range, pagevec_release) to cold path(i.e.,
> lru_add_drain_all, lru_cache_disable).
This code is starting to hurt my brain.
What are the locking/context rules for invalidate_bh_lrus_cpu()?
AFAICT it offers no protection against two CPUs concurrently running
__invalidate_bh_lrus() against the same bh_lru.
So when CONFIG_SMP=y, invalidate_bh_lrus_cpu() must always and only be
run on the cpu which owns the bh_lru. In which case why does it have
the `cpu' arg?
Your new lru_add_and_bh_lrus_drain() follows these rules by calling
invalidate_bh_lrus_cpu() from a per-cpu worker or when CONFIG_SMP=n.
I think. It's all as clear as mud and undocumented. Could you please
take a look at this? Comment the locking/context rules thoroughly and
check that they are being followed? Not forgetting cpu hotplug... See if
there's a way of simplifying/clarifying the code?
The fact that swap.c has those #ifdef CONFIG_SMPs in there is a hint
that we're doing something wrong (or poorly) in there. Perhaps that's
unavoidable because of all the fancy footwork in __lru_add_drain_all().
On Tue, Jun 01, 2021 at 04:15:40PM -0700, Andrew Morton wrote:
> On Tue, 1 Jun 2021 07:54:25 -0700 Minchan Kim <[email protected]> wrote:
>
> > kernel test robot reported the regression of fio.write_iops[1]
> > with [2].
> >
> > Since lru_add_drain is called frequently, invalidate bh_lrus
> > there could increase bh_lrus cache miss ratio, which needs
> > more IO in the end.
> >
> > This patch moves the bh_lrus invalidation from the hot path(
> > e.g., zap_page_range, pagevec_release) to cold path(i.e.,
> > lru_add_drain_all, lru_cache_disable).
>
> This code is starting to hurt my brain.
>
> What are the locking/context rules for invalidate_bh_lrus_cpu()?
> AFAICT it offers no protection against two CPUs concurrently running
> __invalidate_bh_lrus() against the same bh_lru.
The lru_add_drain_per_cpu will run on per-cpu since it's per-cpu work
and invalidate_bh_lrus_cpu will run under bh_lru_lock so I couldn't
imagine that race can happen.
>
> So when CONFIG_SMP=y, invalidate_bh_lrus_cpu() must always and only be
> run on the cpu which owns the bh_lru. In which case why does it have
> the `cpu' arg?
I just wanted to express both lru_add_drain_cpu and invalidate_bh_lrus_cpu
in lru_add_and_bh_lrus_drain run in the same cpu but look like a bad idea
since it makes people confused. Let me remove the cpu argument from
invalidate_bh_lrus_cpu.
>
> Your new lru_add_and_bh_lrus_drain() follows these rules by calling
> invalidate_bh_lrus_cpu() from a per-cpu worker or when CONFIG_SMP=n.
>
> I think. It's all as clear as mud and undocumented. Could you please
> take a look at this? Comment the locking/context rules thoroughly and
> check that they are being followed? Not forgetting cpu hotplug... See if
> there's a way of simplifying/clarifying the code?
>
> The fact that swap.c has those #ifdef CONFIG_SMPs in there is a hint
> that we're doing something wrong (or poorly) in there. Perhaps that's
> unavoidable because of all the fancy footwork in __lru_add_drain_all().
>
Hopefully, this is better.
From 8d58e7ade3ed6c080995dec1395b1e130b3d16b3 Mon Sep 17 00:00:00 2001
From: Minchan Kim <[email protected]>
Date: Tue, 25 May 2021 08:19:17 -0700
Subject: [PATCH] mm: fs: invalidate bh_lrus for only cold path
kernel test robot reported the regression of fio.write_iops[1]
with [2].
Since lru_add_drain is called frequently, invalidate bh_lrus
there could increase bh_lrus cache miss ratio, which needs
more IO in the end.
This patch moves the bh_lrus invalidation from the hot path(
e.g., zap_page_range, pagevec_release) to cold path(i.e.,
lru_add_drain_all, lru_cache_disable).
[1] https://lore.kernel.org/lkml/20210520083144.GD14190@xsang-OptiPlex-9020/
[2] 8cc621d2f45d, mm: fs: invalidate BH LRU during page migration
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
---
fs/buffer.c | 8 ++++++--
include/linux/buffer_head.h | 4 ++--
mm/swap.c | 19 ++++++++++++++++---
3 files changed, 24 insertions(+), 7 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 673cfbef9eec..bdaffed39030 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1487,12 +1487,16 @@ void invalidate_bh_lrus(void)
}
EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
-void invalidate_bh_lrus_cpu(int cpu)
+/*
+ * It's called from workqueue context so we need a bh_lru_lock to close
+ * the race with preemption/irq.
+ */
+void invalidate_bh_lrus_cpu(void)
{
struct bh_lru *b;
bh_lru_lock();
- b = per_cpu_ptr(&bh_lrus, cpu);
+ b = this_cpu_ptr(&bh_lrus);
__invalidate_bh_lrus(b);
bh_lru_unlock();
}
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index e7e99da31349..b04d34bab124 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -194,7 +194,7 @@ void __breadahead_gfp(struct block_device *, sector_t block, unsigned int size,
struct buffer_head *__bread_gfp(struct block_device *,
sector_t block, unsigned size, gfp_t gfp);
void invalidate_bh_lrus(void);
-void invalidate_bh_lrus_cpu(int cpu);
+void invalidate_bh_lrus_cpu(void);
bool has_bh_in_lru(int cpu, void *dummy);
struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
void free_buffer_head(struct buffer_head * bh);
@@ -408,7 +408,7 @@ static inline int inode_has_buffers(struct inode *inode) { return 0; }
static inline void invalidate_inode_buffers(struct inode *inode) {}
static inline int remove_inode_buffers(struct inode *inode) { return 1; }
static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }
-static inline void invalidate_bh_lrus_cpu(int cpu) {}
+static inline void invalidate_bh_lrus_cpu(void) {}
static inline bool has_bh_in_lru(int cpu, void *dummy) { return 0; }
#define buffer_heads_over_limit 0
diff --git a/mm/swap.c b/mm/swap.c
index 1958d5feb148..4d9ec3c3c5a9 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -642,7 +642,6 @@ void lru_add_drain_cpu(int cpu)
pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
activate_page_drain(cpu);
- invalidate_bh_lrus_cpu(cpu);
}
/**
@@ -725,6 +724,20 @@ void lru_add_drain(void)
local_unlock(&lru_pvecs.lock);
}
+/*
+ * It's called from per-cpu workqueue context in SMP case so
+ * lru_add_drain_cpu and invalidate_bh_lrus_cpu should run on
+ * the same cpu. It shouldn't be a problem in !SMP case since
+ * the core is only one and the locks will disable preemption.
+ */
+static void lru_add_and_bh_lrus_drain(void)
+{
+ local_lock(&lru_pvecs.lock);
+ lru_add_drain_cpu(smp_processor_id());
+ local_unlock(&lru_pvecs.lock);
+ invalidate_bh_lrus_cpu();
+}
+
void lru_add_drain_cpu_zone(struct zone *zone)
{
local_lock(&lru_pvecs.lock);
@@ -739,7 +752,7 @@ static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
static void lru_add_drain_per_cpu(struct work_struct *dummy)
{
- lru_add_drain();
+ lru_add_and_bh_lrus_drain();
}
/*
@@ -880,7 +893,7 @@ void lru_cache_disable(void)
*/
__lru_add_drain_all(true);
#else
- lru_add_drain();
+ lru_add_and_bh_lrus_drain();
#endif
}
--
2.32.0.rc0.204.g9fa02ecfa5-goog
On 2021-06-02 15:45, Minchan Kim wrote:
> On Tue, Jun 01, 2021 at 04:15:40PM -0700, Andrew Morton wrote:
>> On Tue, 1 Jun 2021 07:54:25 -0700 Minchan Kim <[email protected]>
>> wrote:
>>
>> > kernel test robot reported the regression of fio.write_iops[1]
>> > with [2].
>> >
>> > Since lru_add_drain is called frequently, invalidate bh_lrus
>> > there could increase bh_lrus cache miss ratio, which needs
>> > more IO in the end.
>> >
>> > This patch moves the bh_lrus invalidation from the hot path(
>> > e.g., zap_page_range, pagevec_release) to cold path(i.e.,
>> > lru_add_drain_all, lru_cache_disable).
>>
>> This code is starting to hurt my brain.
>>
>> What are the locking/context rules for invalidate_bh_lrus_cpu()?
>
>
>> AFAICT it offers no protection against two CPUs concurrently running
>> __invalidate_bh_lrus() against the same bh_lru.
>
> The lru_add_drain_per_cpu will run on per-cpu since it's per-cpu work
> and invalidate_bh_lrus_cpu will run under bh_lru_lock so I couldn't
> imagine that race can happen.
>
>>
>> So when CONFIG_SMP=y, invalidate_bh_lrus_cpu() must always and only be
>> run on the cpu which owns the bh_lru. In which case why does it have
>> the `cpu' arg?
>
> I just wanted to express both lru_add_drain_cpu and
> invalidate_bh_lrus_cpu
> in lru_add_and_bh_lrus_drain run in the same cpu but look like a bad
> idea
> since it makes people confused. Let me remove the cpu argument from
> invalidate_bh_lrus_cpu.
>
>>
>> Your new lru_add_and_bh_lrus_drain() follows these rules by calling
>> invalidate_bh_lrus_cpu() from a per-cpu worker or when CONFIG_SMP=n.
>>
>> I think. It's all as clear as mud and undocumented. Could you please
>> take a look at this? Comment the locking/context rules thoroughly and
>> check that they are being followed? Not forgetting cpu hotplug...
>> See if
>> there's a way of simplifying/clarifying the code?
>>
>> The fact that swap.c has those #ifdef CONFIG_SMPs in there is a hint
>> that we're doing something wrong (or poorly) in there. Perhaps that's
>> unavoidable because of all the fancy footwork in
>> __lru_add_drain_all().
>>
>
> Hopefully, this is better.
>
> From 8d58e7ade3ed6c080995dec1395b1e130b3d16b3 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <[email protected]>
> Date: Tue, 25 May 2021 08:19:17 -0700
> Subject: [PATCH] mm: fs: invalidate bh_lrus for only cold path
>
> kernel test robot reported the regression of fio.write_iops[1]
> with [2].
>
> Since lru_add_drain is called frequently, invalidate bh_lrus
> there could increase bh_lrus cache miss ratio, which needs
> more IO in the end.
>
> This patch moves the bh_lrus invalidation from the hot path(
> e.g., zap_page_range, pagevec_release) to cold path(i.e.,
> lru_add_drain_all, lru_cache_disable).
>
> [1]
> https://lore.kernel.org/lkml/20210520083144.GD14190@xsang-OptiPlex-9020/
> [2] 8cc621d2f45d, mm: fs: invalidate BH LRU during page migration
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Minchan Kim <[email protected]>
> ---
> fs/buffer.c | 8 ++++++--
> include/linux/buffer_head.h | 4 ++--
> mm/swap.c | 19 ++++++++++++++++---
> 3 files changed, 24 insertions(+), 7 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 673cfbef9eec..bdaffed39030 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1487,12 +1487,16 @@ void invalidate_bh_lrus(void)
> }
> EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
>
> -void invalidate_bh_lrus_cpu(int cpu)
> +/*
> + * It's called from workqueue context so we need a bh_lru_lock to
> close
> + * the race with preemption/irq.
> + */
> +void invalidate_bh_lrus_cpu(void)
> {
> struct bh_lru *b;
>
> bh_lru_lock();
> - b = per_cpu_ptr(&bh_lrus, cpu);
> + b = this_cpu_ptr(&bh_lrus);
> __invalidate_bh_lrus(b);
> bh_lru_unlock();
> }
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index e7e99da31349..b04d34bab124 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -194,7 +194,7 @@ void __breadahead_gfp(struct block_device *,
> sector_t block, unsigned int size,
> struct buffer_head *__bread_gfp(struct block_device *,
> sector_t block, unsigned size, gfp_t gfp);
> void invalidate_bh_lrus(void);
> -void invalidate_bh_lrus_cpu(int cpu);
> +void invalidate_bh_lrus_cpu(void);
> bool has_bh_in_lru(int cpu, void *dummy);
> struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
> void free_buffer_head(struct buffer_head * bh);
> @@ -408,7 +408,7 @@ static inline int inode_has_buffers(struct inode
> *inode) { return 0; }
> static inline void invalidate_inode_buffers(struct inode *inode) {}
> static inline int remove_inode_buffers(struct inode *inode) { return
> 1; }
> static inline int sync_mapping_buffers(struct address_space *mapping)
> { return 0; }
> -static inline void invalidate_bh_lrus_cpu(int cpu) {}
> +static inline void invalidate_bh_lrus_cpu(void) {}
> static inline bool has_bh_in_lru(int cpu, void *dummy) { return 0; }
> #define buffer_heads_over_limit 0
>
> diff --git a/mm/swap.c b/mm/swap.c
> index 1958d5feb148..4d9ec3c3c5a9 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -642,7 +642,6 @@ void lru_add_drain_cpu(int cpu)
> pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
>
> activate_page_drain(cpu);
> - invalidate_bh_lrus_cpu(cpu);
> }
>
> /**
> @@ -725,6 +724,20 @@ void lru_add_drain(void)
> local_unlock(&lru_pvecs.lock);
> }
>
> +/*
> + * It's called from per-cpu workqueue context in SMP case so
> + * lru_add_drain_cpu and invalidate_bh_lrus_cpu should run on
> + * the same cpu. It shouldn't be a problem in !SMP case since
> + * the core is only one and the locks will disable preemption.
> + */
> +static void lru_add_and_bh_lrus_drain(void)
> +{
> + local_lock(&lru_pvecs.lock);
> + lru_add_drain_cpu(smp_processor_id());
> + local_unlock(&lru_pvecs.lock);
> + invalidate_bh_lrus_cpu();
> +}
> +
> void lru_add_drain_cpu_zone(struct zone *zone)
> {
> local_lock(&lru_pvecs.lock);
> @@ -739,7 +752,7 @@ static DEFINE_PER_CPU(struct work_struct,
> lru_add_drain_work);
>
> static void lru_add_drain_per_cpu(struct work_struct *dummy)
> {
> - lru_add_drain();
> + lru_add_and_bh_lrus_drain();
> }
>
> /*
> @@ -880,7 +893,7 @@ void lru_cache_disable(void)
> */
> __lru_add_drain_all(true);
> #else
> - lru_add_drain();
> + lru_add_and_bh_lrus_drain();
> #endif
> }
Hi Minchan,
This looks good to me. Feel free to add:
Reviewed-by: Chris Goldsworthy <[email protected]>
Thanks,
Chris.
--
The Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum,
a Linux Foundation Collaborative Project
On Wed, Jun 09, 2021 at 01:52:46PM -0700, Chris Goldsworthy wrote:
> On 2021-06-02 15:45, Minchan Kim wrote:
> > On Tue, Jun 01, 2021 at 04:15:40PM -0700, Andrew Morton wrote:
> > > On Tue, 1 Jun 2021 07:54:25 -0700 Minchan Kim <[email protected]>
> > > wrote:
> > >
> > > > kernel test robot reported the regression of fio.write_iops[1]
> > > > with [2].
> > > >
> > > > Since lru_add_drain is called frequently, invalidate bh_lrus
> > > > there could increase bh_lrus cache miss ratio, which needs
> > > > more IO in the end.
> > > >
> > > > This patch moves the bh_lrus invalidation from the hot path(
> > > > e.g., zap_page_range, pagevec_release) to cold path(i.e.,
> > > > lru_add_drain_all, lru_cache_disable).
> > >
> > > This code is starting to hurt my brain.
> > >
> > > What are the locking/context rules for invalidate_bh_lrus_cpu()?
> >
> >
> > > AFAICT it offers no protection against two CPUs concurrently running
> > > __invalidate_bh_lrus() against the same bh_lru.
> >
> > The lru_add_drain_per_cpu will run on per-cpu since it's per-cpu work
> > and invalidate_bh_lrus_cpu will run under bh_lru_lock so I couldn't
> > imagine that race can happen.
> >
> > >
> > > So when CONFIG_SMP=y, invalidate_bh_lrus_cpu() must always and only be
> > > run on the cpu which owns the bh_lru. In which case why does it have
> > > the `cpu' arg?
> >
> > I just wanted to express both lru_add_drain_cpu and
> > invalidate_bh_lrus_cpu
> > in lru_add_and_bh_lrus_drain run in the same cpu but look like a bad
> > idea
> > since it makes people confused. Let me remove the cpu argument from
> > invalidate_bh_lrus_cpu.
> >
> > >
> > > Your new lru_add_and_bh_lrus_drain() follows these rules by calling
> > > invalidate_bh_lrus_cpu() from a per-cpu worker or when CONFIG_SMP=n.
> > >
> > > I think. It's all as clear as mud and undocumented. Could you please
> > > take a look at this? Comment the locking/context rules thoroughly and
> > > check that they are being followed? Not forgetting cpu hotplug...
> > > See if
> > > there's a way of simplifying/clarifying the code?
> > >
> > > The fact that swap.c has those #ifdef CONFIG_SMPs in there is a hint
> > > that we're doing something wrong (or poorly) in there. Perhaps that's
> > > unavoidable because of all the fancy footwork in
> > > __lru_add_drain_all().
> > >
> >
> > Hopefully, this is better.
> >
> > From 8d58e7ade3ed6c080995dec1395b1e130b3d16b3 Mon Sep 17 00:00:00 2001
> > From: Minchan Kim <[email protected]>
> > Date: Tue, 25 May 2021 08:19:17 -0700
> > Subject: [PATCH] mm: fs: invalidate bh_lrus for only cold path
> >
> > kernel test robot reported the regression of fio.write_iops[1]
> > with [2].
> >
> > Since lru_add_drain is called frequently, invalidate bh_lrus
> > there could increase bh_lrus cache miss ratio, which needs
> > more IO in the end.
> >
> > This patch moves the bh_lrus invalidation from the hot path(
> > e.g., zap_page_range, pagevec_release) to cold path(i.e.,
> > lru_add_drain_all, lru_cache_disable).
> >
> > [1]
> > https://lore.kernel.org/lkml/20210520083144.GD14190@xsang-OptiPlex-9020/
> > [2] 8cc621d2f45d, mm: fs: invalidate BH LRU during page migration
> > Reported-by: kernel test robot <[email protected]>
> > Signed-off-by: Minchan Kim <[email protected]>
> > ---
> > fs/buffer.c | 8 ++++++--
> > include/linux/buffer_head.h | 4 ++--
> > mm/swap.c | 19 ++++++++++++++++---
> > 3 files changed, 24 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/buffer.c b/fs/buffer.c
> > index 673cfbef9eec..bdaffed39030 100644
> > --- a/fs/buffer.c
> > +++ b/fs/buffer.c
> > @@ -1487,12 +1487,16 @@ void invalidate_bh_lrus(void)
> > }
> > EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
> >
> > -void invalidate_bh_lrus_cpu(int cpu)
> > +/*
> > + * It's called from workqueue context so we need a bh_lru_lock to close
> > + * the race with preemption/irq.
> > + */
> > +void invalidate_bh_lrus_cpu(void)
> > {
> > struct bh_lru *b;
> >
> > bh_lru_lock();
> > - b = per_cpu_ptr(&bh_lrus, cpu);
> > + b = this_cpu_ptr(&bh_lrus);
> > __invalidate_bh_lrus(b);
> > bh_lru_unlock();
> > }
> > diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> > index e7e99da31349..b04d34bab124 100644
> > --- a/include/linux/buffer_head.h
> > +++ b/include/linux/buffer_head.h
> > @@ -194,7 +194,7 @@ void __breadahead_gfp(struct block_device *,
> > sector_t block, unsigned int size,
> > struct buffer_head *__bread_gfp(struct block_device *,
> > sector_t block, unsigned size, gfp_t gfp);
> > void invalidate_bh_lrus(void);
> > -void invalidate_bh_lrus_cpu(int cpu);
> > +void invalidate_bh_lrus_cpu(void);
> > bool has_bh_in_lru(int cpu, void *dummy);
> > struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
> > void free_buffer_head(struct buffer_head * bh);
> > @@ -408,7 +408,7 @@ static inline int inode_has_buffers(struct inode
> > *inode) { return 0; }
> > static inline void invalidate_inode_buffers(struct inode *inode) {}
> > static inline int remove_inode_buffers(struct inode *inode) { return 1;
> > }
> > static inline int sync_mapping_buffers(struct address_space *mapping)
> > { return 0; }
> > -static inline void invalidate_bh_lrus_cpu(int cpu) {}
> > +static inline void invalidate_bh_lrus_cpu(void) {}
> > static inline bool has_bh_in_lru(int cpu, void *dummy) { return 0; }
> > #define buffer_heads_over_limit 0
> >
> > diff --git a/mm/swap.c b/mm/swap.c
> > index 1958d5feb148..4d9ec3c3c5a9 100644
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -642,7 +642,6 @@ void lru_add_drain_cpu(int cpu)
> > pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
> >
> > activate_page_drain(cpu);
> > - invalidate_bh_lrus_cpu(cpu);
> > }
> >
> > /**
> > @@ -725,6 +724,20 @@ void lru_add_drain(void)
> > local_unlock(&lru_pvecs.lock);
> > }
> >
> > +/*
> > + * It's called from per-cpu workqueue context in SMP case so
> > + * lru_add_drain_cpu and invalidate_bh_lrus_cpu should run on
> > + * the same cpu. It shouldn't be a problem in !SMP case since
> > + * the core is only one and the locks will disable preemption.
> > + */
> > +static void lru_add_and_bh_lrus_drain(void)
> > +{
> > + local_lock(&lru_pvecs.lock);
> > + lru_add_drain_cpu(smp_processor_id());
> > + local_unlock(&lru_pvecs.lock);
> > + invalidate_bh_lrus_cpu();
> > +}
> > +
> > void lru_add_drain_cpu_zone(struct zone *zone)
> > {
> > local_lock(&lru_pvecs.lock);
> > @@ -739,7 +752,7 @@ static DEFINE_PER_CPU(struct work_struct,
> > lru_add_drain_work);
> >
> > static void lru_add_drain_per_cpu(struct work_struct *dummy)
> > {
> > - lru_add_drain();
> > + lru_add_and_bh_lrus_drain();
> > }
> >
> > /*
> > @@ -880,7 +893,7 @@ void lru_cache_disable(void)
> > */
> > __lru_add_drain_all(true);
> > #else
> > - lru_add_drain();
> > + lru_add_and_bh_lrus_drain();
> > #endif
> > }
>
> Hi Minchan,
>
> This looks good to me. Feel free to add:
>
> Reviewed-by: Chris Goldsworthy <[email protected]>
Thanks for the review, Chris.
Andrew, could you take a look?
On 2021-06-18 15:05, Minchan Kim wrote:
> On Wed, Jun 09, 2021 at 01:52:46PM -0700, Chris Goldsworthy wrote:
>> On 2021-06-02 15:45, Minchan Kim wrote:
>> > On Tue, Jun 01, 2021 at 04:15:40PM -0700, Andrew Morton wrote:
>> > > On Tue, 1 Jun 2021 07:54:25 -0700 Minchan Kim <[email protected]>
>> > > wrote:
>> > >
>> > > > kernel test robot reported the regression of fio.write_iops[1]
>> > > > with [2].
>> > > >
>> > > > Since lru_add_drain is called frequently, invalidate bh_lrus
>> > > > there could increase bh_lrus cache miss ratio, which needs
>> > > > more IO in the end.
>> > > >
>> > > > This patch moves the bh_lrus invalidation from the hot path(
>> > > > e.g., zap_page_range, pagevec_release) to cold path(i.e.,
>> > > > lru_add_drain_all, lru_cache_disable).
>> > >
>> > > This code is starting to hurt my brain.
>> > >
>> > > What are the locking/context rules for invalidate_bh_lrus_cpu()?
>> >
>> >
>> > > AFAICT it offers no protection against two CPUs concurrently running
>> > > __invalidate_bh_lrus() against the same bh_lru.
>> >
>> > The lru_add_drain_per_cpu will run on per-cpu since it's per-cpu work
>> > and invalidate_bh_lrus_cpu will run under bh_lru_lock so I couldn't
>> > imagine that race can happen.
>> >
>> > >
>> > > So when CONFIG_SMP=y, invalidate_bh_lrus_cpu() must always and only be
>> > > run on the cpu which owns the bh_lru. In which case why does it have
>> > > the `cpu' arg?
>> >
>> > I just wanted to express both lru_add_drain_cpu and
>> > invalidate_bh_lrus_cpu
>> > in lru_add_and_bh_lrus_drain run in the same cpu but look like a bad
>> > idea
>> > since it makes people confused. Let me remove the cpu argument from
>> > invalidate_bh_lrus_cpu.
>> >
>> > >
>> > > Your new lru_add_and_bh_lrus_drain() follows these rules by calling
>> > > invalidate_bh_lrus_cpu() from a per-cpu worker or when CONFIG_SMP=n.
>> > >
>> > > I think. It's all as clear as mud and undocumented. Could you please
>> > > take a look at this? Comment the locking/context rules thoroughly and
>> > > check that they are being followed? Not forgetting cpu hotplug...
>> > > See if
>> > > there's a way of simplifying/clarifying the code?
>> > >
>> > > The fact that swap.c has those #ifdef CONFIG_SMPs in there is a hint
>> > > that we're doing something wrong (or poorly) in there. Perhaps that's
>> > > unavoidable because of all the fancy footwork in
>> > > __lru_add_drain_all().
>> > >
>> >
>> > Hopefully, this is better.
>> >
>> > From 8d58e7ade3ed6c080995dec1395b1e130b3d16b3 Mon Sep 17 00:00:00 2001
>> > From: Minchan Kim <[email protected]>
>> > Date: Tue, 25 May 2021 08:19:17 -0700
>> > Subject: [PATCH] mm: fs: invalidate bh_lrus for only cold path
>> >
>> > kernel test robot reported the regression of fio.write_iops[1]
>> > with [2].
>> >
>> > Since lru_add_drain is called frequently, invalidate bh_lrus
>> > there could increase bh_lrus cache miss ratio, which needs
>> > more IO in the end.
>> >
>> > This patch moves the bh_lrus invalidation from the hot path(
>> > e.g., zap_page_range, pagevec_release) to cold path(i.e.,
>> > lru_add_drain_all, lru_cache_disable).
>> >
>> > [1]
>> > https://lore.kernel.org/lkml/20210520083144.GD14190@xsang-OptiPlex-9020/
>> > [2] 8cc621d2f45d, mm: fs: invalidate BH LRU during page migration
>> > Reported-by: kernel test robot <[email protected]>
>> > Signed-off-by: Minchan Kim <[email protected]>
>> > ---
>> > fs/buffer.c | 8 ++++++--
>> > include/linux/buffer_head.h | 4 ++--
>> > mm/swap.c | 19 ++++++++++++++++---
>> > 3 files changed, 24 insertions(+), 7 deletions(-)
>> >
>> > diff --git a/fs/buffer.c b/fs/buffer.c
>> > index 673cfbef9eec..bdaffed39030 100644
>> > --- a/fs/buffer.c
>> > +++ b/fs/buffer.c
>> > @@ -1487,12 +1487,16 @@ void invalidate_bh_lrus(void)
>> > }
>> > EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
>> >
>> > -void invalidate_bh_lrus_cpu(int cpu)
>> > +/*
>> > + * It's called from workqueue context so we need a bh_lru_lock to close
>> > + * the race with preemption/irq.
>> > + */
>> > +void invalidate_bh_lrus_cpu(void)
>> > {
>> > struct bh_lru *b;
>> >
>> > bh_lru_lock();
>> > - b = per_cpu_ptr(&bh_lrus, cpu);
>> > + b = this_cpu_ptr(&bh_lrus);
>> > __invalidate_bh_lrus(b);
>> > bh_lru_unlock();
>> > }
>> > diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
>> > index e7e99da31349..b04d34bab124 100644
>> > --- a/include/linux/buffer_head.h
>> > +++ b/include/linux/buffer_head.h
>> > @@ -194,7 +194,7 @@ void __breadahead_gfp(struct block_device *,
>> > sector_t block, unsigned int size,
>> > struct buffer_head *__bread_gfp(struct block_device *,
>> > sector_t block, unsigned size, gfp_t gfp);
>> > void invalidate_bh_lrus(void);
>> > -void invalidate_bh_lrus_cpu(int cpu);
>> > +void invalidate_bh_lrus_cpu(void);
>> > bool has_bh_in_lru(int cpu, void *dummy);
>> > struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
>> > void free_buffer_head(struct buffer_head * bh);
>> > @@ -408,7 +408,7 @@ static inline int inode_has_buffers(struct inode
>> > *inode) { return 0; }
>> > static inline void invalidate_inode_buffers(struct inode *inode) {}
>> > static inline int remove_inode_buffers(struct inode *inode) { return 1;
>> > }
>> > static inline int sync_mapping_buffers(struct address_space *mapping)
>> > { return 0; }
>> > -static inline void invalidate_bh_lrus_cpu(int cpu) {}
>> > +static inline void invalidate_bh_lrus_cpu(void) {}
>> > static inline bool has_bh_in_lru(int cpu, void *dummy) { return 0; }
>> > #define buffer_heads_over_limit 0
>> >
>> > diff --git a/mm/swap.c b/mm/swap.c
>> > index 1958d5feb148..4d9ec3c3c5a9 100644
>> > --- a/mm/swap.c
>> > +++ b/mm/swap.c
>> > @@ -642,7 +642,6 @@ void lru_add_drain_cpu(int cpu)
>> > pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
>> >
>> > activate_page_drain(cpu);
>> > - invalidate_bh_lrus_cpu(cpu);
>> > }
>> >
>> > /**
>> > @@ -725,6 +724,20 @@ void lru_add_drain(void)
>> > local_unlock(&lru_pvecs.lock);
>> > }
>> >
>> > +/*
>> > + * It's called from per-cpu workqueue context in SMP case so
>> > + * lru_add_drain_cpu and invalidate_bh_lrus_cpu should run on
>> > + * the same cpu. It shouldn't be a problem in !SMP case since
>> > + * the core is only one and the locks will disable preemption.
>> > + */
>> > +static void lru_add_and_bh_lrus_drain(void)
>> > +{
>> > + local_lock(&lru_pvecs.lock);
>> > + lru_add_drain_cpu(smp_processor_id());
>> > + local_unlock(&lru_pvecs.lock);
>> > + invalidate_bh_lrus_cpu();
>> > +}
>> > +
>> > void lru_add_drain_cpu_zone(struct zone *zone)
>> > {
>> > local_lock(&lru_pvecs.lock);
>> > @@ -739,7 +752,7 @@ static DEFINE_PER_CPU(struct work_struct,
>> > lru_add_drain_work);
>> >
>> > static void lru_add_drain_per_cpu(struct work_struct *dummy)
>> > {
>> > - lru_add_drain();
>> > + lru_add_and_bh_lrus_drain();
>> > }
>> >
>> > /*
>> > @@ -880,7 +893,7 @@ void lru_cache_disable(void)
>> > */
>> > __lru_add_drain_all(true);
>> > #else
>> > - lru_add_drain();
>> > + lru_add_and_bh_lrus_drain();
>> > #endif
>> > }
>>
>> Hi Minchan,
>>
>> This looks good to me. Feel free to add:
>>
>> Reviewed-by: Chris Goldsworthy <[email protected]>
>
> Thanks for the review, Chris.
>
> Andrew, could you take a look?
Hi Andrew,
Have you been able to look over the second version of Minchan's patch?
Thanks,
Chris.
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