From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 0CFA96B000C for ; Mon, 26 Mar 2018 11:09:48 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id c16so9583349pgv.8 for ; Mon, 26 Mar 2018 08:09:48 -0700 (PDT) Received: from EUR02-AM5-obe.outbound.protection.outlook.com (mail-eopbgr00130.outbound.protection.outlook.com. [40.107.0.130]) by mx.google.com with ESMTPS id e127si10139533pgc.170.2018.03.26.08.09.46 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 26 Mar 2018 08:09:46 -0700 (PDT) Subject: Re: [PATCH 01/10] mm: Assign id to every memcg-aware shrinker References: <152163840790.21546.980703278415599202.stgit@localhost.localdomain> <152163847740.21546.16821490541519326725.stgit@localhost.localdomain> <20180324184009.dyjlt4rj4b6y6sz3@esperanza> From: Kirill Tkhai Message-ID: <0db2d93f-12cd-d703-fce7-4c3b8df5bc12@virtuozzo.com> Date: Mon, 26 Mar 2018 18:09:35 +0300 MIME-Version: 1.0 In-Reply-To: <20180324184009.dyjlt4rj4b6y6sz3@esperanza> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov 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 Hi, Vladimir, thanks for your review! On 24.03.2018 21:40, Vladimir Davydov wrote: > 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? Ok >> /* 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? I think it won't be better, since we allocate memory under this semaphore. After we use shrinker_rwsem, we'll have to allocate the memory with GFP_ATOMIC, which does not seems good. Currently, the patchset makes shrinker_rwsem be taken for a small time, just to assign already allocated memory to maps. >> +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. I saw mnt_alloc_group_id() does the same, so this was the reason, the additional variable was used. Doesn't this gives a good advise to ida and makes it find a free id faster? >> + if (!ret) { >> + shrinker->id = id; >> + bitmap_id_start = shrinker->id + 1; >> + } >> + up_write(&bitmap_rwsem); >> + if (ret == -EAGAIN) >> + goto retry; >> + >> + return ret; >> +} Thanks, Kirill