| Message ID | 20210601145425.1396981-1-minchan@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] mm: fs: invalidate bh_lrus for only cold path | expand |
On Tue, 1 Jun 2021 07:54:25 -0700 Minchan Kim <minchan@kernel.org> 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 <minchan@kernel.org> 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 <minchan@kernel.org> 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 <oliver.sang@intel.com> Signed-off-by: Minchan Kim <minchan@kernel.org> --- 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 }
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 <minchan@kernel.org> >> 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 <minchan@kernel.org> > 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 <oliver.sang@intel.com> > Signed-off-by: Minchan Kim <minchan@kernel.org> > --- > 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 <cgoldswo@codeaurora.org> Thanks, Chris.
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 <minchan@kernel.org> > > > 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 <minchan@kernel.org> > > 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 <oliver.sang@intel.com> > > Signed-off-by: Minchan Kim <minchan@kernel.org> > > --- > > 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 <cgoldswo@codeaurora.org> 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 <minchan@kernel.org> >> > > 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 <minchan@kernel.org> >> > 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 <oliver.sang@intel.com> >> > Signed-off-by: Minchan Kim <minchan@kernel.org> >> > --- >> > 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 <cgoldswo@codeaurora.org> > > 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.
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 }