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Date: Mon, 12 Dec 2016 12:09:59 -0500
From: Tejun Heo <tj@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>,
linux-kernel@...r.kernel.org,
Lai Jiangshan <jiangshanlai@...il.com>,
Jens Axboe <axboe@...nel.dk>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-block@...r.kernel.org, dri-devel@...ts.freedesktop.org,
Matthew Wilcox <mawilcox@...rosoft.com>
Subject: Re: [RFC 00/10] implement alternative and much simpler id allocator
Hello,
On Fri, Dec 09, 2016 at 02:01:40PM -0800, Andrew Morton wrote:
> On Thu, 8 Dec 2016 02:22:55 +0100 Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
>
> > TL;DR: these patches save 250 KB of memory, with more low-hanging
> > fruit ready to pick.
> >
> > While browsing through the lib/idr.c code, I noticed that the code at
> > the end of ida_get_new_above() probably doesn't work as intended: Most
> > users of ida use it via ida_simple_get(), and that starts by
> > unconditionally calling ida_pre_get(), ensuring that ida->idr has
> > 8==MAX_IDR_FREE idr_layers in its free list id_free. In the common
> > case, none (or at most one) of these get used during
> > ida_get_new_above(), and we only free one, leaving at least 6 (usually
> > 7) idr_layers in the free list.
>
> Please be aware of
>
> http://ozlabs.org/~akpm/mmots/broken-out/reimplement-idr-and-ida-using-the-radix-tree.patch
> http://lkml.kernel.org/r/1480369871-5271-68-git-send-email-mawilcox@linuxonhyperv.com
>
> I expect we'll be merging patches 1-32 of that series into 4.10-rc1 and
> the above patch (#33) into 4.11-rc1.
Ah, yeah, great to see the silly implementation being replaced the
radix tree. ida_pre_get() looks suspicious tho. idr_preload()
immedicately being followed by idr_preload_end() probably is broken.
Maybe what we need is moving ida to idr like preload interface and
then convert it to radix based interface? ida currently assumes
per-ida preloading.
Thanks.
--
tejun
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