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Thu, 10 Jun 2021 08:32:14 +0000 To: Cyrill Gorcunov Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christoph Lameter , David Rientjes , Pekka Enberg , Joonsoo Kim , Sebastian Andrzej Siewior , Thomas Gleixner , Mel Gorman , Jesper Dangaard Brouer , Peter Zijlstra , Jann Horn References: <20210609113903.1421-1-vbabka@suse.cz> <20210609113903.1421-30-vbabka@suse.cz> From: Vlastimil Babka Subject: Re: [RFC v2 29/34] mm: slub: Move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context Message-ID: Date: Thu, 10 Jun 2021 10:32:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=knI7HCq6; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="f/oIQ2VA"; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=knI7HCq6; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="f/oIQ2VA"; dmarc=none; spf=pass (imf04.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Stat-Signature: 8ocuxhzfujpdztm16bz3fzojhjxz35cj X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 573A037C X-HE-Tag: 1623313933-116874 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 6/10/21 12:29 AM, Cyrill Gorcunov wrote: > On Wed, Jun 09, 2021 at 01:38:58PM +0200, Vlastimil Babka wrote: >> +static DEFINE_MUTEX(flush_lock); >> +static DEFINE_PER_CPU(struct slub_flush_work, slub_flush); >> + >> static void flush_all(struct kmem_cache *s) >> { >> - on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1); >> + struct slub_flush_work *sfw; >> + unsigned int cpu; >> + >> + cpus_read_lock(); >> + mutex_lock(&flush_lock); >> + >=20 > Hi, Vlastimil! Could you please point why do you lock cpus first and > mutex only after? Why not mutex_lock + cpus_read_lock instead? Good question! I must admit I didn't think about it much and just followe= d the order that was in the original Sebastian's patch [1] But there was a good reason for this order as some paths via __kmem_cache_shutdown() and __kmem_cache_shrink() were alreadu called und= er cpus_read_lock. Meanwhile mainline (me, actually) removed those, so now i= t doesn't seem to be a need to keep this order anymore and we could switch = it. Thanks, Vlastimil [1] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tre= e/patches/0005-mm-slub-Move-flush_cpu_slab-invocations-__free_slab-.patch= ?h=3Dlinux-5.12.y-rt-patches