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@xxxxxxxxxx> > > > 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@xxxxxxxxxx> > > 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@xxxxxxxxx> > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > --- > > 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@xxxxxxxxxxxxxx> Thanks for the review, Chris. Andrew, could you take a look?
