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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH 5/6] mm/page_alloc: Protect PCP lists with a spinlock Content-Language: en-US To: Nicolas Saenz Julienne , Mel Gorman Cc: Marcelo Tosatti , Michal Hocko , LKML , Linux-MM References: <20220420095906.27349-1-mgorman@techsingularity.net> <20220420095906.27349-6-mgorman@techsingularity.net> <0d6bf5a97777bec1e0b425f2fb33dbb80d848621.camel@redhat.com> From: Vlastimil Babka In-Reply-To: <0d6bf5a97777bec1e0b425f2fb33dbb80d848621.camel@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 61CF91A004A X-Stat-Signature: aq9kmo741fpn7u4bs5kmgbdhmhob4n5u X-Rspam-User: Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=0WxDKb6V; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=iOjoOWFB; spf=pass (imf19.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Rspamd-Server: rspam09 X-HE-Tag: 1650991730-473551 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 4/26/22 18:42, Nicolas Saenz Julienne wrote: > On Wed, 2022-04-20 at 10:59 +0100, Mel Gorman wrote: >> @@ -3082,15 +3093,22 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order, >> */ >> void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp) >> { >> - unsigned long flags; >> int to_drain, batch; >> >> - local_lock_irqsave(&pagesets.lock, flags); >> batch = READ_ONCE(pcp->batch); >> to_drain = min(pcp->count, batch); >> - if (to_drain > 0) >> + if (to_drain > 0) { >> + unsigned long flags; >> + >> + /* free_pcppages_bulk expects IRQs disabled for zone->lock */ >> + local_irq_save(flags); > > Why dropping the local_lock? That approach is nicer to RT builds, and I don't > think it makes a difference from a non-RT perspective. I think the separate irq_disable+spin_lock here is actually broken on RT config, as explained in Documentation/locking/locktypes.rst. pcp->lock would have to be a raw_spin_lock. > That said, IIUC, this will eventually disappear with subsequent patches, right? So it wouldn't be mergeable even as a temporary step. > >> + >> + spin_lock(&pcp->lock); >> free_pcppages_bulk(zone, to_drain, pcp, 0); >> - local_unlock_irqrestore(&pagesets.lock, flags); >> + spin_unlock(&pcp->lock); >> + >> + local_irq_restore(flags); >> + } >> } >> #endif >>