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Message-ID: <d6182b74-5879-4e5a-8605-abd55542215d@bytedance.com>
Date:   Tue, 10 Oct 2023 11:03:39 +0800
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Subject: Re: [PATCH 2/3] maple_tree: use preallocations in mas_store_gfp()
To:     Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc:     akpm@linux-foundation.org, willy@infradead.org,
        liam.howlett@oracle.com, zhangpeng.00@bytedance.com,
        linux-kernel@vger.kernel.org, maple-tree@lists.infradead.org,
        linux-mm@kvack.org
References: <20231009201639.920512-1-sidhartha.kumar@oracle.com>
 <20231009201639.920512-3-sidhartha.kumar@oracle.com>
From:   Peng Zhang <zhangpeng.00@bytedance.com>
In-Reply-To: <20231009201639.920512-3-sidhartha.kumar@oracle.com>
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Hi,

在 2023/10/10 04:16, Sidhartha Kumar 写道:
> Preallocate maple nodes before call to mas_wr_store_entry(). If a new
> node is not needed, go directly to mas_wr_store_entry(), otherwise
> allocate the needed nodes and set the MA_STATE_PREALLOC flag.
> 
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> ---
>   lib/maple_tree.c | 22 +++++++++++++++++++---
>   1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index e239197a57fc..25ae66e585f4 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -5478,17 +5478,33 @@ int mas_prealloc_calc(struct ma_wr_state *wr_mas)
>   int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp)
>   {
>   	MA_WR_STATE(wr_mas, mas, entry);
> +	int request;
>   
>   	mas_wr_store_setup(&wr_mas);
> -	trace_ma_write(__func__, mas, 0, entry);
> -retry:
> +	wr_mas.content = mas_start(mas);
> +
> +	request = mas_prealloc_calc(&wr_mas);
mas_wr_store_entry() does something similar to mas_prealloc_calc().
Now, making it do it twice would incur additional overhead.
We encountered this issue while optimizing preallocation, but it
hasn't been resolved yet. Previously, this problem only occurred
when using mas_preallocate(). Now, this change would bring this
impact to all write operations on maple tree. What do you think
about it?

Thanks,
Peng
> +	if (!request)
> +		goto store_entry;
> +
> +	mas_node_count_gfp(mas, request, gfp);
> +	if (unlikely(mas_is_err(mas))) {
> +		mas_set_alloc_req(mas, 0);
> +		mas_destroy(mas);
> +		mas_reset(mas);
> +		return xa_err(mas->node);
> +	}
> +	mas->mas_flags |= MA_STATE_PREALLOC;
> +
> +store_entry:
>   	mas_wr_store_entry(&wr_mas);
>   	if (unlikely(mas_nomem(mas, gfp)))
> -		goto retry;
> +		goto store_entry;
>   
>   	if (unlikely(mas_is_err(mas)))
>   		return xa_err(mas->node);
>   
> +	trace_ma_write(__func__, mas, 0, entry);
>   	return 0;
>   }
>   EXPORT_SYMBOL_GPL(mas_store_gfp);