Re: [RFC PATCH linux 2/2] fs/proc: use a hash table for the directory entries

[Nicolas Dichtel]

Le 02/10/2014 18:46, Stephen Hemminger a écrit :
> On Thu,  2 Oct 2014 17:25:01 +0200
> Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx> wrote:
>
> > From: Thierry Herbelot <thierry.herbelot@xxxxxxxxx>
> >
> > 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@xxxxxxxxx>
> > Signed-off-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
>
> 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.
Right, I will rework this after looking at rbtree.
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