On Mon 22-05-17 12:08:49, Pavel Tatashin wrote:
> Allow hash tables to scale with memory but at slower pace, when HASH_ADAPT
> is provided every time memory quadruples the sizes of hash tables will only
> double instead of quadrupling as well. This algorithm starts working only
> when memory size reaches a certain point, currently set to 64G.
>
> This is example of dentry hash table size, before and after four various
> memory configurations:
>
> MEMORY SCALE HASH_SIZE
> old new old new
> 8G 13 13 8M 8M
> 16G 13 13 16M 16M
> 32G 13 13 32M 32M
> 64G 13 13 64M 64M
> 128G 13 14 128M 64M
> 256G 13 14 256M 128M
> 512G 13 15 512M 128M
> 1024G 13 15 1024M 256M
> 2048G 13 16 2048M 256M
> 4096G 13 16 4096M 512M
> 8192G 13 17 8192M 512M
> 16384G 13 17 16384M 1024M
> 32768G 13 18 32768M 1024M
> 65536G 13 18 65536M 2048M
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/page_alloc.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8afa63e81e73..409e0cd35381 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7169,6 +7169,21 @@ static unsigned long __init arch_reserved_kernel_pages(void)
> #endif
>
> /*
> + * Adaptive scale is meant to reduce sizes of hash tables on large memory
> + * machines. As memory size is increased the scale is also increased but at
> + * slower pace. Starting from ADAPT_SCALE_BASE (64G), every time memory
> + * quadruples the scale is increased by one, which means the size of hash table
> + * only doubles, instead of quadrupling as well.
> + * Because 32-bit systems cannot have large physical memory, where this scaling
> + * makes sense, it is disabled on such platforms.
> + */
> +#if __BITS_PER_LONG > 32
> +#define ADAPT_SCALE_BASE (64ul << 30)
> +#define ADAPT_SCALE_SHIFT 2
> +#define ADAPT_SCALE_NPAGES (ADAPT_SCALE_BASE >> PAGE_SHIFT)
> +#endif
> +
> +/*
> * allocate a large system hash table from bootmem
> * - it is assumed that the hash table must contain an exact power-of-2
> * quantity of entries
> @@ -7199,6 +7214,16 @@ void *__init alloc_large_system_hash(const char *tablename,
> if (PAGE_SHIFT < 20)
> numentries = round_up(numentries, (1<<20)/PAGE_SIZE);
>
> +#if __BITS_PER_LONG > 32
> + if (!high_limit) {
> + unsigned long adapt;
> +
> + for (adapt = ADAPT_SCALE_NPAGES; adapt < numentries;
> + adapt <<= ADAPT_SCALE_SHIFT)
> + scale++;
> + }
> +#endif
> +
> /* limit to 1 bucket per 2^scale bytes of low memory */
> if (scale > PAGE_SHIFT)
> numentries >>= (scale - PAGE_SHIFT);
> --
> 2.13.0
--
Michal Hocko
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
