RE: [PATCH 04/12] percpu: manage chunks based on contig_bits instead of free_bytes

[Peng Fan]

> -----Original Message-----
> From: owner-linux-mm@xxxxxxxxx [mailto:owner-linux-mm@xxxxxxxxx] On
> Behalf Of Dennis Zhou
> Sent: 2019年2月28日 10:19
> To: Dennis Zhou <dennis@xxxxxxxxxx>; Tejun Heo <tj@xxxxxxxxxx>; Christoph
> Lameter <cl@xxxxxxxxx>
> Cc: Vlad Buslov <vladbu@xxxxxxxxxxxx>; kernel-team@xxxxxx;
> linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: [PATCH 04/12] percpu: manage chunks based on contig_bits instead
> of free_bytes
> 
> When a chunk becomes fragmented, it can end up having a large number of
> small allocation areas free. The free_bytes sorting of chunks leads to
> unnecessary checking of chunks that cannot satisfy the allocation.
> Switch to contig_bits sorting to prevent scanning chunks that may not be able
> to service the allocation request.
> 
> Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx>
> ---
>  mm/percpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/percpu.c b/mm/percpu.c
> index b40112b2fc59..c996bcffbb2a 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -234,7 +234,7 @@ static int pcpu_chunk_slot(const struct pcpu_chunk
> *chunk)
>  	if (chunk->free_bytes < PCPU_MIN_ALLOC_SIZE || chunk->contig_bits
> == 0)
>  		return 0;
> 
> -	return pcpu_size_to_slot(chunk->free_bytes);
> +	return pcpu_size_to_slot(chunk->contig_bits * PCPU_MIN_ALLOC_SIZE);
>  }
> 
>  /* set the pointer to a chunk in a page struct */

Reviewed-by: Peng Fan <peng.fan@xxxxxxx>

Not relevant to this patch, another optimization to percpu might be good
to use per chunk spin_lock, not gobal pcpu_lock.

Thanks,
Peng.

> --
> 2.17.1