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SubjectRe: [RESEND][PATCH v2] mm: don't call lru draining in the nested lru_cache_disable
On Thu, Dec 30, 2021 at 11:36:27AM -0800, Minchan Kim wrote:
> lru_cache_disable involves IPIs to drain pagevec of each core,
> which sometimes takes quite long time to complete depending
> on cpu's business, which makes allocation too slow up to
> sveral hundredth milliseconds. Furthermore, the repeated draining
> in the alloc_contig_range makes thing worse considering caller
> of alloc_contig_range usually tries multiple times in the loop.
>
> This patch makes the lru_cache_disable aware of the fact the
> pagevec was already disabled. With that, user of alloc_contig_range
> can disable the lru cache in advance in their context during the
> repeated trial so they can avoid the multiple costly draining
> in cma allocation.

Hi Folks,

Any comment to proceed the work?

>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> * from v1 - https://lore.kernel.org/lkml/20211206221006.946661-1-minchan@kernel.org/
> * fix lru_cache_disable race - akpm
>
> include/linux/swap.h | 14 ++------------
> mm/cma.c | 5 +++++
> mm/swap.c | 30 ++++++++++++++++++++++++++++--
> 3 files changed, 35 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index ba52f3a3478e..fe18e86a4f13 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -348,19 +348,9 @@ extern void lru_note_cost_page(struct page *);
> extern void lru_cache_add(struct page *);
> extern void mark_page_accessed(struct page *);
>
> -extern atomic_t lru_disable_count;
> -
> -static inline bool lru_cache_disabled(void)
> -{
> - return atomic_read(&lru_disable_count);
> -}
> -
> -static inline void lru_cache_enable(void)
> -{
> - atomic_dec(&lru_disable_count);
> -}
> -
> +extern bool lru_cache_disabled(void);
> extern void lru_cache_disable(void);
> +extern void lru_cache_enable(void);
> extern void lru_add_drain(void);
> extern void lru_add_drain_cpu(int cpu);
> extern void lru_add_drain_cpu_zone(struct zone *zone);
> diff --git a/mm/cma.c b/mm/cma.c
> index 995e15480937..60be555c5b95 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -30,6 +30,7 @@
> #include <linux/cma.h>
> #include <linux/highmem.h>
> #include <linux/io.h>
> +#include <linux/swap.h>
> #include <linux/kmemleak.h>
> #include <trace/events/cma.h>
>
> @@ -453,6 +454,8 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> if (bitmap_count > bitmap_maxno)
> goto out;
>
> + lru_cache_disable();
> +
> for (;;) {
> spin_lock_irq(&cma->lock);
> bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap,
> @@ -492,6 +495,8 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> start = bitmap_no + mask + 1;
> }
>
> + lru_cache_enable();
> +
> trace_cma_alloc_finish(cma->name, pfn, page, count, align);
>
> /*
> diff --git a/mm/swap.c b/mm/swap.c
> index af3cad4e5378..5f89d7c9a54e 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -847,7 +847,17 @@ void lru_add_drain_all(void)
> }
> #endif /* CONFIG_SMP */
>
> -atomic_t lru_disable_count = ATOMIC_INIT(0);
> +static atomic_t lru_disable_count = ATOMIC_INIT(0);
> +
> +bool lru_cache_disabled(void)
> +{
> + return atomic_read(&lru_disable_count) != 0;
> +}
> +
> +void lru_cache_enable(void)
> +{
> + atomic_dec(&lru_disable_count);
> +}
>
> /*
> * lru_cache_disable() needs to be called before we start compiling
> @@ -859,7 +869,21 @@ atomic_t lru_disable_count = ATOMIC_INIT(0);
> */
> void lru_cache_disable(void)
> {
> - atomic_inc(&lru_disable_count);
> + static DEFINE_MUTEX(lock);
> +
> + /*
> + * The lock gaurantees lru_cache is drained when the function
> + * returned.
> + */
> + mutex_lock(&lock);
> + /*
> + * If someone is already disabled lru_cache, just return with
> + * increasing the lru_disable_count.
> + */
> + if (atomic_inc_not_zero(&lru_disable_count)) {
> + mutex_unlock(&lock);
> + return;
> + }
> #ifdef CONFIG_SMP
> /*
> * lru_add_drain_all in the force mode will schedule draining on
> @@ -873,6 +897,8 @@ void lru_cache_disable(void)
> #else
> lru_add_and_bh_lrus_drain();
> #endif
> + atomic_inc(&lru_disable_count);
> + mutex_unlock(&lock);
> }
>
> /**
> --
> 2.34.1.448.ga2b2bfdf31-goog
>

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