linux-kernel - Re: [PATCH 2/2 -mm] mm: account lazy free pages into available memory

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Date:   Mon, 8 Jul 2019 15:53:05 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     rientjes@...gle.com, kirill.shutemov@...ux.intel.com,
        mhocko@...e.com, hannes@...xchg.org, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2 -mm] mm: account lazy free pages into available memory

And how about this one?


On 6/27/19 10:12 AM, Yang Shi wrote:
> Available memory is one of the most important metrics for memory
> pressure.  Currently, lazy free pages are not accounted into available
> memory, but they are reclaimable actually, like reclaimable slabs.
>
> Accounting lazy free pages into available memory should reflect the real
> memory pressure status, and also would help administrators and/or other
> high level scheduling tools make better decision.
>
> The /proc/meminfo would show more available memory with test which
> creates ~1GB deferred split THP.
>
> Before:
> MemAvailable:   43544272 kB
> ...
> AnonHugePages:     10240 kB
> ShmemHugePages:        0 kB
> ShmemPmdMapped:        0 kB
> LazyFreePages:   1046528 kB
>
> After:
> MemAvailable:   44415124 kB
> ...
> AnonHugePages:      6144 kB
> ShmemHugePages:        0 kB
> ShmemPmdMapped:        0 kB
> LazyFreePages:   1046528 kB
>
> MADV_FREE pages are not accounted for NR_LAZYFREE since they have been
> put on inactive file LRU and accounted into available memory.
> Accounting here would double account them.
>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> ---
>   mm/page_alloc.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cab50e8..58ceca5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5005,6 +5005,7 @@ long si_mem_available(void)
>   	unsigned long wmark_low = 0;
>   	unsigned long pages[NR_LRU_LISTS];
>   	unsigned long reclaimable;
> +	unsigned long lazyfree;
>   	struct zone *zone;
>   	int lru;
>   
> @@ -5038,6 +5039,10 @@ long si_mem_available(void)
>   			global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE);
>   	available += reclaimable - min(reclaimable / 2, wmark_low);
>   
> +	/* Lazyfree pages are reclaimable when memory pressure is hit */
> +	lazyfree = global_node_page_state(NR_LAZYFREE);
> +	available += lazyfree - min(lazyfree / 2, wmark_low);
> +
>   	if (available < 0)
>   		available = 0;
>   	return available;