From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1522142107; cv=none; d=google.com; s=arc-20160816; b=QUBK10VedfRTJFJaL4mkcEsG4o3vZN34Nl5KOSk14IbK+mqP0bQKADW752TdDSSJ49 7LPf/a1Ny8aZR4Xwz+5nbBozw1ARUAEwL3yGvJbFyiWmRF4GFr/yMw4CzbNkJ4B6NOYL zPAX58LCJcSPlAF8/hv8JDD0bxAOjD6Cu7DXwJTZl7DqJMjGq1cHFZJ5qi2Yzlg0WX+3 nofsJswgURbMraGfV81rKLPJ7CuwYx1EIh7u5N9ThLOomHLL6uGbIrBBeKJTn4W50soI 5Iaw/O1k1+LgaWBiJt/kv/yDJF7atCC40Sh/BLlX+jF0remSyn681DdsXKEHZNZ7WwOZ 73KQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:dkim-signature:arc-authentication-results; bh=IP/5640eGTm+lrGD5tbDl1YAcA61UWl2gH7Q5QFclp4=; b=TVOnuFgZ7AERMVQVEUlFD2KRgJJVxB/hnbSl675sZI80EhEH4ijF8L9rr2alKhkY68 ZbBOK3gdezaAjD9y3I+pQ0/4Ml9QSGo346lxgC2RgtgcEGmCSsgQH3cqdiEwdroPkoxg 89xzBRiUi81fUun646co1IT+nNWD6v4gzvmZ0sWiN2ea5vSKgPCssqOAYyApi0P51XHf Q1lDiT9eudOqT3+SGxSF2y+VuPasDnlWsvh/4IPbBtDXrw81x2E36VVYwuBQ9dsDR7WC hcw0EDZul+ts10tze7NBww1udI8notW0gCTitJnObd+WsBqoM72FJ4UsZPHNLV8GO9vn yZEQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=BGbmCrXw; spf=pass (google.com: domain of vdavydov.dev@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=vdavydov.dev@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=BGbmCrXw; spf=pass (google.com: domain of vdavydov.dev@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=vdavydov.dev@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com X-Google-Smtp-Source: AG47ELuFeJZZN5ZLnbG/P+FkBwjbf56bi+LPmkHgYluqYGQDEP9ZGgRdVBP0HKEqlxuoa7znBhStyg== Date: Tue, 27 Mar 2018 12:15:04 +0300 From: Vladimir Davydov 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 Subject: Re: [PATCH 01/10] mm: Assign id to every memcg-aware shrinker Message-ID: <20180327091504.zcqvr3mkuznlgwux@esperanza> References: <152163840790.21546.980703278415599202.stgit@localhost.localdomain> <152163847740.21546.16821490541519326725.stgit@localhost.localdomain> <20180324184009.dyjlt4rj4b6y6sz3@esperanza> <0db2d93f-12cd-d703-fce7-4c3b8df5bc12@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0db2d93f-12cd-d703-fce7-4c3b8df5bc12@virtuozzo.com> X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1595553598792007322?= X-GMAIL-MSGID: =?utf-8?q?1596081682915121119?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Mon, Mar 26, 2018 at 06:09:35PM +0300, Kirill Tkhai wrote: > 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. AFAIR it's OK to sleep under an rwsem so GFP_ATOMIC wouldn't be necessary. Anyway, we only need to allocate memory when we extend shrinker bitmaps, which is rare. In fact, there can only be a limited number of such calls, as we never shrink these bitmaps (which is fine by me). > > >> +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? As Matthew pointed out, this is rather pointless.