linux-kernel - Re: [PATCH 2/8] mm, truncate: Do not check mapping for every page being truncated

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Date:   Thu, 12 Oct 2017 14:15:27 +0200
From:   Jan Kara <jack@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Linux-MM <linux-mm@...ck.org>,
        Linux-FSDevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH 2/8] mm, truncate: Do not check mapping for every page
 being truncated

On Thu 12-10-17 10:30:57, Mel Gorman wrote:
> During truncation, the mapping has already been checked for shmem and dax
> so it's known that workingset_update_node is required. This patch avoids
> the checks on mapping for each page being truncated. In all other cases,
> a lookup helper is used to determine if workingset_update_node() needs
> to be called. The one danger is that the API is slightly harder to use as
> calling workingset_update_node directly without checking for dax or shmem
> mappings could lead to surprises. However, the API rarely needs to be used
> and hopefully the comment is enough to give people the hint.
> 
> sparsetruncate (tiny)
>                               4.14.0-rc4             4.14.0-rc4
>                              oneirq-v1r1        pickhelper-v1r1
> Min          Time      141.00 (   0.00%)      140.00 (   0.71%)
> 1st-qrtle    Time      142.00 (   0.00%)      141.00 (   0.70%)
> 2nd-qrtle    Time      142.00 (   0.00%)      142.00 (   0.00%)
> 3rd-qrtle    Time      143.00 (   0.00%)      143.00 (   0.00%)
> Max-90%      Time      144.00 (   0.00%)      144.00 (   0.00%)
> Max-95%      Time      147.00 (   0.00%)      145.00 (   1.36%)
> Max-99%      Time      195.00 (   0.00%)      191.00 (   2.05%)
> Max          Time      230.00 (   0.00%)      205.00 (  10.87%)
> Amean        Time      144.37 (   0.00%)      143.82 (   0.38%)
> Stddev       Time       10.44 (   0.00%)        9.00 (  13.74%)
> Coeff        Time        7.23 (   0.00%)        6.26 (  13.41%)
> Best99%Amean Time      143.72 (   0.00%)      143.34 (   0.26%)
> Best95%Amean Time      142.37 (   0.00%)      142.00 (   0.26%)
> Best90%Amean Time      142.19 (   0.00%)      141.85 (   0.24%)
> Best75%Amean Time      141.92 (   0.00%)      141.58 (   0.24%)
> Best50%Amean Time      141.69 (   0.00%)      141.31 (   0.27%)
> Best25%Amean Time      141.38 (   0.00%)      140.97 (   0.29%)
> 
> As you'd expect, the gain is marginal but it can be detected. The differences
> in bonnie are all within the noise which is not surprising given the impact
> on the microbenchmark.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
...
> diff --git a/mm/workingset.c b/mm/workingset.c
> index 7119cd745ace..a80d52387734 100644
> --- a/mm/workingset.c
> +++ b/mm/workingset.c
> @@ -341,12 +341,6 @@ static struct list_lru shadow_nodes;
>  
>  void workingset_update_node(struct radix_tree_node *node, void *private)
>  {
> -	struct address_space *mapping = private;
> -
> -	/* Only regular page cache has shadow entries */
> -	if (dax_mapping(mapping) || shmem_mapping(mapping))
> -		return;
> -

Hum, we don't need to pass 'mapping' from call sites then? Either pass NULL
or just remove the argument completely since nobody needs it anymore...
Otherwise the patch looks good.

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR