From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26D43C433B4 for ; Fri, 9 Apr 2021 11:01:26 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AF6B8610D1 for ; Fri, 9 Apr 2021 11:01:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AF6B8610D1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4EFC36B006C; Fri, 9 Apr 2021 07:01:25 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4C6F26B006E; Fri, 9 Apr 2021 07:01:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 366C06B0070; Fri, 9 Apr 2021 07:01:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0244.hostedemail.com [216.40.44.244]) by kanga.kvack.org (Postfix) with ESMTP id 19D636B006C for ; Fri, 9 Apr 2021 07:01:25 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id CB6CB1EF1 for ; Fri, 9 Apr 2021 11:01:24 +0000 (UTC) X-FDA: 78012537288.12.9B84CBE Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf09.hostedemail.com (Postfix) with ESMTP id 079C160006EE for ; Fri, 9 Apr 2021 11:00:21 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9B536B147; Fri, 9 Apr 2021 11:00:22 +0000 (UTC) Subject: Re: [PATCH 1/2] mm/vmscan: add sync_shrinkers function To: =?UTF-8?Q?Christian_K=c3=b6nig?= , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: ray.huang@amd.com, daniel@ffwll.ch, akpm@linux-foundation.org References: <20210409071725.1532-1-christian.koenig@amd.com> From: Vlastimil Babka Message-ID: <462c2a51-4aa8-47ba-1c67-171ca651b016@suse.cz> Date: Fri, 9 Apr 2021 13:00:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210409071725.1532-1-christian.koenig@amd.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Stat-Signature: sdn9ionz76yddo17c5fgqz5nfudzqpgg X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 079C160006EE Received-SPF: none (suse.cz>: No applicable sender policy available) receiver=imf09; identity=mailfrom; envelope-from=""; helo=mx2.suse.de; client-ip=195.135.220.15 X-HE-DKIM-Result: none/none X-HE-Tag: 1617966021-383739 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 4/9/21 9:17 AM, Christian K=C3=B6nig wrote: > To be able to switch to a spinlock and reduce lock contention in the TT= M > shrinker we don't want to hold a mutex while unmapping and freeing page= s > from the pool. Does using spinlock instead of mutex really reduce lock contention? > But then we somehow need to prevent a race between (for example) the sh= rinker > trying to free pages and hotplug trying to remove the device which thos= e pages > belong to. >=20 > Taking and releasing the shrinker semaphore on the write side after > unmapping and freeing all pages should make sure that no shrinker is ru= nning in > paralell any more. So you explain this in this commit log for adding the function, but then = the next patch just adds a sync_shrinkers() call without any comment. I would= expect there a comment explaining why it's done there - what it protects against= , as it's not an obvious pattern IMHO. > Signed-off-by: Christian K=C3=B6nig > --- > include/linux/shrinker.h | 1 + > mm/vmscan.c | 10 ++++++++++ > 2 files changed, 11 insertions(+) >=20 > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h > index 0f80123650e2..6b75dc372fce 100644 > --- a/include/linux/shrinker.h > +++ b/include/linux/shrinker.h > @@ -92,4 +92,5 @@ extern void register_shrinker_prepared(struct shrinke= r *shrinker); > extern int register_shrinker(struct shrinker *shrinker); > extern void unregister_shrinker(struct shrinker *shrinker); > extern void free_prealloced_shrinker(struct shrinker *shrinker); > +extern void sync_shrinkers(void); > #endif > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 562e87cbd7a1..46cd9c215d73 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -408,6 +408,16 @@ void unregister_shrinker(struct shrinker *shrinker= ) > } > EXPORT_SYMBOL(unregister_shrinker); > =20 > +/** > + * sync_shrinker - Wait for all running shrinkers to complete. > + */ > +void sync_shrinkers(void) > +{ > + down_write(&shrinker_rwsem); > + up_write(&shrinker_rwsem); > +} > +EXPORT_SYMBOL(sync_shrinkers); > + > #define SHRINK_BATCH 128 > =20 > static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, >=20