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Message-ID: <20141002094657.1e28e027@urahara>
Date: Thu, 2 Oct 2014 09:46:57 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
davem@...emloft.net, ebiederm@...ssion.com,
akpm@...ux-foundation.org, adobriyan@...il.com,
rui.xiang@...wei.com, viro@...iv.linux.org.uk, oleg@...hat.com,
gorcunov@...nvz.org, kirill.shutemov@...ux.intel.com,
grant.likely@...retlab.ca, tytso@....edu,
Thierry Herbelot <thierry.herbelot@...nd.com>
Subject: Re: [RFC PATCH linux 2/2] fs/proc: use a hash table for the
directory entries
On Thu, 2 Oct 2014 17:25:01 +0200
Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:
> From: Thierry Herbelot <thierry.herbelot@...nd.com>
>
> The current implementation for the directories in /proc is using a single
> linked list. This is slow when handling directories with large numbers of
> entries (eg netdevice-related entries when lots of tunnels are opened).
>
> This patch enables multiple linked lists. A hash based on the entry name is
> used to select the linked list for one given entry.
>
> The speed creation of netdevices is faster as shorter linked lists must be
> scanned when adding a new netdevice.
>
> Here are some numbers:
>
> dummy30000.batch contains 30 000 times 'link add type dummy'.
>
> Before the patch:
> time ip -b dummy30000.batch
> real 2m32.221s
> user 0m0.380s
> sys 2m30.610s
>
> After the patch:
> time ip -b dummy30000.batch
> real 1m57.190s
> user 0m0.350s
> sys 1m56.120s
>
> The single 'subdir' list head is replaced by a subdir hash table. The subdir
> hash buckets are only allocated for directories. The number of hash buckets
> is a compile-time parameter.
>
> For all functions which handle directory entries, an additional check on the
> directory nature of the dir entry ensures that pde_hash_buckets was allocated.
> This check was not needed as subdir was present for all dir entries, whether
> actual directories or simple files.
>
> Signed-off-by: Thierry Herbelot <thierry.herbelot@...nd.com>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
I think the speed up is a good idea and makes sense.
It would be better to use exist hlist macros for hash table rather than
open coding it.
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