From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f71.google.com (mail-lf0-f71.google.com [209.85.215.71]) by kanga.kvack.org (Postfix) with ESMTP id CF5F16B0009 for ; Sat, 24 Mar 2018 14:40:14 -0400 (EDT) Received: by mail-lf0-f71.google.com with SMTP id p202-v6so4878428lfe.3 for ; Sat, 24 Mar 2018 11:40:14 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id g77-v6sor3021607lfl.87.2018.03.24.11.40.12 for (Google Transport Security); Sat, 24 Mar 2018 11:40:12 -0700 (PDT) Date: Sat, 24 Mar 2018 21:40:09 +0300 From: Vladimir Davydov Subject: Re: [PATCH 01/10] mm: Assign id to every memcg-aware shrinker Message-ID: <20180324184009.dyjlt4rj4b6y6sz3@esperanza> References: <152163840790.21546.980703278415599202.stgit@localhost.localdomain> <152163847740.21546.16821490541519326725.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <152163847740.21546.16821490541519326725.stgit@localhost.localdomain> Sender: owner-linux-mm@kvack.org List-ID: To: Kirill Tkhai Cc: viro@zeniv.linux.org.uk, hannes@cmpxchg.org, mhocko@kernel.org, akpm@linux-foundation.org, tglx@linutronix.de, pombredanne@nexb.com, stummala@codeaurora.org, gregkh@linuxfoundation.org, sfr@canb.auug.org.au, guro@fb.com, mka@chromium.org, penguin-kernel@I-love.SAKURA.ne.jp, chris@chris-wilson.co.uk, longman@redhat.com, minchan@kernel.org, hillf.zj@alibaba-inc.com, ying.huang@intel.com, mgorman@techsingularity.net, shakeelb@google.com, jbacik@fb.com, linux@roeck-us.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org Hello Kirill, I don't have any objections to the idea behind this patch set. Well, at least I don't know how to better tackle the problem you describe in the cover letter. Please, see below for my comments regarding implementation details. On Wed, Mar 21, 2018 at 04:21:17PM +0300, Kirill Tkhai wrote: > The patch introduces shrinker::id number, which is used to enumerate > memcg-aware shrinkers. The number start from 0, and the code tries > to maintain it as small as possible. > > This will be used as to represent a memcg-aware shrinkers in memcg > shrinkers map. > > Signed-off-by: Kirill Tkhai > --- > include/linux/shrinker.h | 1 + > mm/vmscan.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 60 insertions(+) > > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h > index a3894918a436..738de8ef5246 100644 > --- a/include/linux/shrinker.h > +++ b/include/linux/shrinker.h > @@ -66,6 +66,7 @@ struct shrinker { > > /* These are for internal use */ > struct list_head list; > + int id; This definition could definitely use a comment. BTW shouldn't we ifdef it? > /* objs pending delete, per node */ > atomic_long_t *nr_deferred; > }; > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 8fcd9f8d7390..91b5120b924f 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -159,6 +159,56 @@ unsigned long vm_total_pages; > static LIST_HEAD(shrinker_list); > static DECLARE_RWSEM(shrinker_rwsem); > > +#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB) > +static DEFINE_IDA(bitmap_id_ida); > +static DECLARE_RWSEM(bitmap_rwsem); Can't we reuse shrinker_rwsem for protecting the ida? > +static int bitmap_id_start; > + > +static int alloc_shrinker_id(struct shrinker *shrinker) > +{ > + int id, ret; > + > + if (!(shrinker->flags & SHRINKER_MEMCG_AWARE)) > + return 0; > +retry: > + ida_pre_get(&bitmap_id_ida, GFP_KERNEL); > + down_write(&bitmap_rwsem); > + ret = ida_get_new_above(&bitmap_id_ida, bitmap_id_start, &id); AFAIK ida always allocates the smallest available id so you don't need to keep track of bitmap_id_start. > + if (!ret) { > + shrinker->id = id; > + bitmap_id_start = shrinker->id + 1; > + } > + up_write(&bitmap_rwsem); > + if (ret == -EAGAIN) > + goto retry; > + > + return ret; > +}