From: Minchan Kim <minchan@xxxxxxxxxx> Subject: 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). "Xing, Zhengjun" confirmed : I test the patch, the regression reduced to -2.9%. [1] https://lore.kernel.org/lkml/20210520083144.GD14190@xsang-OptiPlex-9020/ [2] 8cc621d2f45d, mm: fs: invalidate BH LRU during page migration Link: https://lkml.kernel.org/r/20210907212347.1977686-1-minchan@xxxxxxxxxx Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> Reviewed-by: Chris Goldsworthy <cgoldswo@xxxxxxxxxxxxxx> Tested-by: "Xing, Zhengjun" <zhengjun.xing@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/buffer.c | 8 ++++++-- include/linux/buffer_head.h | 4 ++-- mm/swap.c | 19 ++++++++++++++++--- 3 files changed, 24 insertions(+), 7 deletions(-) --- a/fs/buffer.c~mm-fs-invalidate-bh_lrus-for-only-cold-path +++ a/fs/buffer.c @@ -1425,12 +1425,16 @@ 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(); } --- a/include/linux/buffer_head.h~mm-fs-invalidate-bh_lrus-for-only-cold-path +++ a/include/linux/buffer_head.h @@ -194,7 +194,7 @@ void __breadahead_gfp(struct block_devic 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(stru 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 false; } #define buffer_heads_over_limit 0 --- a/mm/swap.c~mm-fs-invalidate-bh_lrus-for-only-cold-path +++ a/mm/swap.c @@ -620,7 +620,6 @@ void lru_add_drain_cpu(int cpu) pagevec_lru_move_fn(pvec, lru_lazyfree_fn); activate_page_drain(cpu); - invalidate_bh_lrus_cpu(cpu); } /** @@ -703,6 +702,20 @@ 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); @@ -717,7 +730,7 @@ static DEFINE_PER_CPU(struct work_struct static void lru_add_drain_per_cpu(struct work_struct *dummy) { - lru_add_drain(); + lru_add_and_bh_lrus_drain(); } /* @@ -858,7 +871,7 @@ void lru_cache_disable(void) */ __lru_add_drain_all(true); #else - lru_add_drain(); + lru_add_and_bh_lrus_drain(); #endif } _
